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Electrical Specifications Subject to Change
LTC6802-1 Multicell Battery Stack Monitor FEATURES
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DESCRIPTION
The LTC(R)6802-1 is a complete battery monitoring IC that includes a 12-bit ADC, a precision voltage reference, a high voltage input multiplexer and a serial interface. Each LTC6802-1 can measure up to 12 series connected battery cells with an input common mode voltage up to 60V. Using a unique level-shifting serial interface, multiple LTC6802-1 devices can be connected in series, without optocouplers or isolators, allowing for monitoring of every cell in a long string of series-connected batteries. When multiple LTC6802-1 devices are connected in series they can operate simultaneously, permitting all cell voltages in the stack to be measured within 13ms. To minimize power, the LTC6802-1 offers a measure mode to monitor each cell for overvoltage and undervoltage conditions. A standby mode is also provided. Each cell input has an associated MOSFET switch for discharging overcharged cells. The related LTC6802-2 offers an individually addressable serial interface.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
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Measures up to 12 Li-Ion Cells in Series (60V Max) Stackable Architecture Enables >1000V Systems 0.25% Maximum Total Measurement Error 13ms to Measure All Cells in a System Cell Balancing: On-Chip Passive Cell Balancing Switches Provision for Off-Chip Passive Balancing Two Thermistor Inputs Plus On-board Temperature Sensor 1MHz Serial Interface with Packet Error Checking High EMI Immunity Delta Sigma Converter With Built In Noise Filter Open Wire Connection Fault Detection Low Power Modes 44-Lead SSOP Package
APPLICATIONS
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Electric and Hybrid Electric Vehicles High Power Portable Equipment Backup Battery Systems High Voltage Data Acquisition Systems
TYPICAL APPLICATION
Typical Application
NEXT 12-CELL PACK ABOVE V+ LTC6802-1 SERIAL DATA TO LTC6802-1 ABOVE DIE TEMP
Measurement Error Over Extended Temperature
0.30 0.25 MEASUREMENT ERROR (%) 0.20 0.15 0.10 0.05 0 -0.05 -0.10 -0.15 -0.20 -0.25 -0.30 -50
REGISTERS AND CONTROL 12-CELL BATTERY STRING MUX 12-BIT ADC
V- NEXT 12-CELL PACK BELOW
10ppm VOLTAGE REFERENCE EXTERNAL TEMP
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SERIAL DATA TO LTC6802-1 BELOW
-25
0 25 50 75 TEMPERATURE (C)
100
125
100k 100k NTC
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LTC6802-1 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 1 2 3 4 5 6 7 8 9 44 CSBI 43 SDO 42 SDI 41 SCKI 40 VMODE 39 GPIO2 38 GPIO1 37 WDTB 36 MMB 25 TOS 34 VREG 33 VREF 32 VTEMP2 31 VTEMP1 30 NC 29 V- 28 S1 27 C1 26 S2 25 C2 24 S3 23 C3
Total Supply Voltage (V+ to V-) .................................60V Input Voltage (Relative to V-) C1 ............................................................ -0.7V to 9V C12 ..........................................V+ - 0.7V to V+ + 0.7V Sn pins ............................... Cn-1 - 0.7V to Cn-1 + 9V CSBO, SCKO, SDOI ..................V+ - 1.4V to V+ + 0.7V All other pins ........................................... -0.7V to 7V Voltage Between Inputs Cn to Cn-1 ............................................... -0.7V to 9V Input Current All Pins ............................................................10mA Operating Temperature Range.................. -40C to 85C Specified Temperature Range .................. -40C to 85C Junction Temperature ........................................... 150C Storage Temperature Range................... -65C to 150C *n = 2 to 11
S10 10 C9 11 S9 12 C8 13 S8 14 C7 15 S7 16 C6 17 S6 18 C5 19 S5 20 C4 21 S4 22
G PACKAGE 44-LEAD PLASTIC SSOP TJMAX = 150C, JA = 70C/W
ORDER INFORMATION
LEAD FREE FINISH LTC6802IG-1#PBF TAPE AND REEL LTC6802IG-1#TRPBF PART MARKING LTC6802IG-1 PACKAGE DESCRIPTION 44-Lead Plastic SSOP TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LTC6802-1 ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER DC Specifications VACC Measurement Resolution ADC Offset Voltage ADC Gain Error VERR Total Measurement Error Quantization of the ADC (Note 2) (Note 2) (Note 4) VCELL = 0V VCELL = 2.3V VCELL = 2.3V VCELL = 3.6V VCELL = 3.6V VCELL = 4.2V VCELL = 4.2V VCELL = 4.6V VTEMP = 2.3V VTEMP = 3.6V VTEMP = 4.2V Full Scale Voltage Range Range of Inputs C4 thru C11 Range of Input C3 Range of Inputs C1, C2 Programmed for 4.2V Programmed for 2.3V Error in Measurement at 125C RLOAD = 100k to V-
l l l l l l l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V+ = 43.2V, V- = 0V, unless otherwise noted.
CONDITIONS MIN TYP 1.5 -0.5 -0.12 -0.22 0.75
l l l
MAX
UNITS mV/Bit
0.5 0.12 0.22
mV % % mV mV mV mV mV mV mV mV mV mV mV V V V V V V C V V ppm/C ppm ppm/khr
-2.76 -5.06 -4.32 -7.92 -5.04 -9.24 8 -2.76 -4.32 -5.04 5.175 3.7 1.8 0 4.182 2.290 3.040 3.035 4.200 2.300 3.072 3.072 5 100 60
2.76 5.06 4.32 7.92 5.04 9.24 2.76 4.32 5.04 V+ 15 10 4.218 2.310 10 3.105 3.110
VCELL VCM
Cell Voltage Range Common Mode Voltage Range Measured Relative to V- Overvoltage (OV) Detection Level Undervoltage (UV) Detection Level Die Temperature Measurement Error
VREF
Reference Pin Voltage Reference Voltage Temperature Coefficient Reference Voltage Thermal Hysteresis Reference Voltage Long Term Drift
25C to 85C and 25C to -40C 10 < V+ < 50, No Load ILOAD = 4mA VERR Specifications Met Timing Specifications Met In/Out of Pins C1 Thru C12 When Measuring Cells When Not Measuring Cells Current Into the V+ Pin when Measuring Voltages with the ADC Average Current Into the V+ Pin While Monitoring for UV and OV Conditions Continuous Monitoring Monitor Every 130ms Monitor Every 500ms Monitor Every 2s Current into the V+ Pin When Idle All Serial Port Pins at Logic `1' Current into the V+ Pin During Serial Communications. All Serial Port Pins at Logic `0' VMODE = 0, This Current is Added to IS or IQS
l l l l l l l l
VREG
Regulator Pin Voltage Regulator Pin Short Circuit Current Limit
4.5 4.1 5 10 4 -10
5.0 5.0
5.5
V V mA V V A pA mA mA
VS IB
Supply Voltage, V+ Relative to V- Input Bias Current
50 50 10 100 1 1.1 1.2
IS IM
Supply Current, Active Supply Current, Monitor Mode
950 300 175 130 50 3.1 3.0 3.6 55 60 4.3 4.5
A A A A A A mA mA
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IQS ICS
Supply Current, Idle Supply Current, Serial I/O
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LTC6802-1 ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER Discharge Switch On-Resistance Temperature Range Thermal Shutdown Temperature Thermal Shutdown Hysteresis Voltage Mode Timing Specifications tCYCLE Measurement Cycle Time Time Required to Measure 11 or 12 Cells Time Required to Measure Up to 10 Cells Time Required to Measure 1 Cell
l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. V+ = 43.2V, V- = 0V, unless otherwise noted.
CONDITIONS VCELL > 3V (Note 3)
l l
MIN -40
TYP 10 145 5
MAX 20 85
UNITS C C C
13 11 2 10 200 400 400 400 100 100 200 1 1 2 600 300 300 300 2 0.8 0.3 3 1000 -1500 -5 1000 -1500 -5 1200 -1200 -3 3 1200 -1200 -3 5 1500 -1000 0 5 1500 -1000
ms ms ms ns ns ns ns ns ns ns ns MHz s ns ns ns ns V V V A A A A A A A A
t1 t2 t3 t4 t5 t6 t7 t8
SDI Valid to SCKI Rising Setup SDI Valid to SCKI Rising Hold SCKI Low SCKI High CSBI Pulse Width SCKI Rising to CSBI Rising CSBI Falling to SCKI Rising SCKI Falling to SDO Valid Clock Frequency Watchdog Timer Time Out Period
l l l l l l l l l l l l l l l l l l l l l l l l l
Timing Specifications tPD1 tPD2 tPD3 tPD4 VIH VIL VOL IIH1 IIL1 IIH2 IIL2 IOH1 IOL1 IOH2 IOL2 CSBI to CSBO SCKI to SCKO SDI to SDOI Write Delay SDOI to SDO Read Delay Digital Input Voltage High Digital Input Voltage Low Digital Output Voltage Low Digital Input Current High Digital Input Current Low Digital Input Current High Digital Input Current Low Digital Output Current High Digital Output Current Low Digital Output Current High Digital Output Current Low CCSBO = 150pF CSCKO = 150pF CSDOI = 150pF CSDO = 150pF Pins VMODE, SCKI, SDI, and CSBI Pins VMODE, SCKI, SDI, and CSBI Pin SDO; Sinking 500A Pins CSBI, SCKI, and SDI (Write) Pins CSBI, SCKI, and SDI (Write) Pin SDOI (Read) Pin SDOI (Read) Pins CSBO, SCKO, and SDOI (Write) Pins CSBO, SCKO, and SDOI (Write) Pin SDI (Read) Pin SDI (Read)
Voltage Mode Digital I/O Specifications
Current Mode Digital I/O Specifications
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2. The ADC specifications are guaranteed by the Total Measurement Error (VERR) specification.
Note 3. Due to the contact resistance of the production tester, this specification is tested to relaxed limits. The 20 limit is guaranteed by design. Note 4. VCELL refers to the voltage applied across the following pin combinations: V+ to C11, Cn to Cn-1 for n = 2 to 11, C1 to V-. VTEMP refers to the voltage applied from VTEMP1 or VTEMP2 to V-
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LTC6802-1 PIN FUNCTIONS
CSBO (Pin 1): Chip Select Output (Active Low). CSBO is a buffered version of the chip select input, CSBI. CSBO drives the next IC in the daisy chain. See Serial Port in the Applications Information section. SDOI (Pin 2): Serial Data I/O Pin. SDOI transfers data to and from the next IC in the daisy chain. See Serial Port in the Applications Information section. SCKO (Pin 3): Serial Clock Output. SCKO is a buffered version of SCKI. SCKO drives the next IC in the daisy chain. See Serial Port in the Applications Information section. V+ (Pin 4): Tie pin 4 to the most positive potential in the battery stack. Typically V+ is the same potential as C12. C12, C11, C10, C9, C8, C7, C6, C5, C4, C3, C2, C1 (Pins 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27): C1 through C12 are the inputs for monitoring battery cell voltages. Up to 12 cells can be monitored. The lowest potential is tied to pin V-. The next lowest potential is tied to C1 and so forth. See the figures in the Applications Information section for more details on connecting batteries to the LTC6802-1. The LTC6802-1 can monitor a series connection of up to 12 cells. The LTC6802-1 cannot monitor parallel combinations of series cells. For example, 3 parallel groups of 4 series cells are not allowed. S12, S11, S10, S9, S8, S7, S6, S5, S4, S3, S2, S1 (Pins 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28): S1 though S12 pins are used to balance battery cells. If one cell in a series becomes over charged, an S output can be used to discharge the cell. Each S output has an internal N-channel MOSFET for discharging. See the Block Diagram. The NMOS has a maximum on resistance of 20. An external resistor should be connected in series with the NMOS to dissipate heat outside of the LTC6802-1 package. When using the internal MOSFETs to discharge cells, the die temperature should be monitored. See Power Dissipation and Thermal Shutdown in the Applications Information section. The S pins also feature an internal 10k pull-up resistor. This allows the S pins to be used to drive the gates of external MOSFETs for higher discharge capability. V- (Pin 29): Connect V- to the most negative potential in the series of cells. NC (Pin 30): Pin 30 is internally connected to V- through 10. Pin 30 can be left unconnected or connected to pin 29 on the PCB. VTEMP1, VTEMP2 (Pins 31, 32): Temperature Sensor Inputs. The ADC measures the voltage on VTEMPx with respect to V- and stores the result in the TMP registers. The ADC measurements are relative to the VREF pin voltage. Therefore a simple thermistor and resistor combination connected to the VREF pin can be used to monitor temperature. The VTEMP inputs can also be general purpose ADC inputs. Any voltage from 0V to 5.125V referenced to V- can be measured. VREF (Pin 33): 3.075V Voltage Reference Output. This pin should be bypassed with a 1F capacitor. The VREF pin can drive a 100k resistive load connected to V-. Larger loads should be buffered with an LT6003 op amp, or similar device. VREG (Pin 34): Linear Voltage Regulator Output. This pin should be bypassed with a 1F capacitor. The VREG pin is capable of supplying up to 4mA to an external load. The VREG pin does not sink current. TOS (Pin 35): Top of Stack Input. Tie TOS to VREG when the LTC6802-1 is the top device in a daisy chain. Tie TOS to V- when the LTC6802-1 is any other device in a daisy chain. When TOS is tied to VREG, the LTC6802-1 ignores the SDOI input. When TOS is tied to V-, the LTC6802-1 expects data to be passed to and from the SDOI pin. MMB (Pin 36): Monitor Mode (Active Low) Input. When MMB is low (same potential as V-), the LTC6802-1 goes into monitor mode. See Modes of Operation in the Applications Information section. WDTB (Pin 37): Watchdog Timer Output (Active Low). If there is no activity on the SCKI pin for 2 seconds, the WDTB output is asserted. The WDTB pin is an open drain NMOS output. When asserted it pulls the output down to V- and resets the configuration register to its default state. The watchdog timer function can be disabled by setting WDTEN = 0 in the configuration register. See Watchdog Timer Circuit in the Applications Information section.
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LTC6802-1 PIN FUNCTIONS
GPIO1, GPIO2 (Pins 38, 39): General Purpose Input/Output. The operation of these pins depends on the state of the MMB pin. When MMB is high, the pins behave as traditional GPIOs. By writing a "0" to a GPIO configuration register bit, the open drain output is activated and the pin is pulled to V-. By writing a logic "1" to the configuration register bit, the corresponding GPIO pin is high impedance. An external resistor is needed to pull the pin up to VREG. By reading the configuration register locations GPIO1 and GPIO2, the state of the pins can be determined. For example, if a "0" is written to register bit GPIO1, a "0" is always read back because the output NMOSFET pulls pin 38 to V-. If a "1" is written to register bit GPIO1, the pin becomes high impedance. Either a "1" or a "0" is read back, depending on the voltage present at pin 38. The GPIOs makes it possible to turn on/off circuitry around the LTC6802-1, or read logic values from a circuit around the LTC6802-1. When the MMB pin is low, the GPIO pins and the WDTB pin are treated as inputs that set the number of cells to be monitored. See Monitor Mode in the Applications Information section. VMODE (Pin 40): Voltage Mode Input. When VMODE is tied to VREG, the SCKI, SDI, SDO, and CSBI pins are configured as voltage inputs and outputs. This means these pins accept standard TTL logic levels. Connect VMODE to VREG when the LTC6802-1 is the bottom device in a daisy chain. When VMODE is connected to V-, the SCKI, SDI, and CSBI pins are configured as current inputs and outputs, and SDO is unused. Connect VMODE to V- when the LTC6802-1 is being driven by another LTC6802-1 in a daisy chain. SCKI (Pin 41): Serial Clock Input. The SCKI pin interfaces to any logic gate (TTL levels) if VMODE is tied to VREG. SCKI must be driven by the SCKO pin of another LTC6802-1 if VMODE is tied to V-. See Serial Port in the Applications Information section. SDI (Pin 42): Serial Data Input. The SDI pin interfaces to any logic gate (TTL levels) if VMODE is tied to VREG. SDI must be driven by the SDOI pin of another LTC6802-1 if VMODE is tied to V-. See Serial Port in the Applications Information section. SDO (Pin 43): Serial Data Output. The SDO pin is an NMOS open drain output if VMODE is tied to VREG. SDO is not used if VMODE is tied to V-. See Serial Port in the Applications Information section. CSBI (Pin 44): Chip Select (Active Low) Input. The CSBI pin interfaces to any logic gate (TTL levels) if VMODE is tied to VREG. CSBI must be driven by the CSBO pin of another LTC6802-1 if VMODE is tied to V-. See Serial Port in the Applications Information section.
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LTC6802-1 BLOCK DIAGRAM
4 V+
5
C12 10k
REGULATOR
VREG
34
6
S12
WATCHDOG TIMER
WDTB
37
7
C11 SCKO SDOI 10k CSBO 3 2 1
24
S3 MUX
A/D CONVERTER
12
25
RESULTS REGISTER AND COMMUNICATIONS
CSBI SDO SDI
44 43 42 41
C2 10k
26
S2 SCKI
27
C1 10k
REFERENCE
VMODE GPIO2
40 39 38 36 35
28
S1
CONTROL
GPIO1 MMB
29
V- 10
TOS DIE TEMP VTEMP1 31 EXTERNAL TEMP VTEMP2 32 VREF 33
30
NC
68021 BD
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LTC6802-1 TIMING DIAGRAM
Timing Diagram of the Serial Interface
t1 t2 SCKI t4 t3 t6 t7
SDI
D3
D2
D1
D0
D7 ... D4
D3
t5 CSBI t8 D4 PREVIOUS COMMAND D3 D2 D1 D0 D7 ... D4 CURRENT COMMAND D3
6915 TD
SDO
OPERATION
THEORY OF OPERATION The LTC6802-1 is a data acquisition IC capable of measuring the voltage of 12 series connected battery cells. An input multiplexer connects the batteries to a 12-bit delta-sigma analog to digital converter (ADC). An internal 10ppm voltage reference combined with the ADC give the LTC6802-1 its outstanding measurement accuracy. The inherent benefits of the delta-sigma ADC vs other types of ADCs (e.g. successive approximation) are explained in Advantages of Delta-Sigma ADCs in the Applications Information section. Communication between the LTC6802-1 and a host processor is handled by a SPI compatible serial interface. As shown in Figure 1, the LTC6802-1's can pass data up and down a stack of devices using simple diodes for isolation. This operation is described in Serial Port in the Applications Information section. The LTC6802-1 also contains circuitry to balance cell voltages. Internal MOSFETs can be used to discharge cells. These internal MOSFETs can also be used to control external balancing circuits. Figure 1 illustrates cell balancing by internal discharge. Figure 4 shows the S pin controlling an external balancing circuit. It is important to note that the LTC6802-1 makes no decisions about turning on/off the internal MOSFETs. This is completely controlled by the host processor. The host processor writes values to a configuration register inside the LTC6802-1 to control the switches. The watchdog timer on the LTC6802-1 can be used to turn off the discharge switches if communication with the host processor is interrupted. OPEN CONNECTION DETECTION The open connection detection algorithm assures that an open circuit is not misinterpreted as a valid cell reading. In the absence of external noise filtering, the input resistance of the ADC will cause open wires to produce a near zero reading. Internal current sources can be used to determine if the wire is truly open. For example, an open on input C3 will result in a near zero reading for both cells connected to C3. For illustration these cells are labeled B3 and B4 in Figure 2. If a near zero reading is encountered for B3 and B4, the MPU can command the LTC6802-1 to place 100A current sources from the ADC inputs to V-. If input C3 is open, the new reading will show B3 to be zero and B4 to be full-scale. Some applications may include external noise filtering to improve the quality of the ADC readings. When an RC network is used to filter noise, an open wire may not produce
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LTC6802-1 OPERATION
BATTERY POSITIVE 350V CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 LTC6802-1 IC #8 CSBI SDO SDI SCKI BATTERIES #25-#84 AND LTC6802-1 ICs #3-#7 CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 LTC6802-1 IC #2
VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
CSBI SDO SDI SCKI
VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4
LTC6802-1 IC #1
V2- OE2 CSBI SDO SDI SCKI V2+ V2-
V1- OE1 CS MISO MOSI CLK V1- V1+ 3V
3V MPU
MODULE IO
VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
DIGITAL ISOLATOR
68021 F01
Figure 1. 96-Cell Battery Stack, Daisy Chain Interface. This Application Schematic illustrates the Simplest Possible System
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LTC6802-1 OPERATION
LTC6802-1
DISCHARGING DURING CELL MEASUREMENTS The primary cell voltage A/D measurement commands (STCVAD and STOWAD) automatically turn off a cell's discharge switch while its voltage is being measured. The discharge switches for the cell above and the cell below will also be turned off during the measurement. For example, discharge switches S4, S5, and S6 will be disabled while cell 5 is being measured.
C4 B4 C3 B3 C2 C1 V- MUX
100A
68021 F02
Figure 2. Open Connection
a zero reading because the ADC input resistance is too large to discharge the capacitors on the input pin. Consider the example in Figure 3 where input C3 is open. After several cycles of measuring battery cells B3 and B4, the ADC input resistance charges capacitors CF3 and CF4. The resulting potential on input C3 will be approximately midway between C2 and C4. The ADC readings of B3 and B4 may indicate a valid cell voltage when in fact the exact state of B3 and B4 is unknown. If the 100A current sources are engaged, the potential at C3 will be pulled down. The ADC reading for B3 will approach zero and the reading for B4 will approach full scale. The amount of change in the cell voltage reading is a function of the external filter capacitor and time that the 100A current sources are connected to the cell.
LTC6802-1
In some systems it may be desirable to allow discharging to continue during cell voltage measurements. The cell voltage A/D conversion commands STCVDC and STOWDC allow any enabled discharge switches to remain on during cell voltage measurements. This feature allows the system to perform a self-test to verify the discharge functionality and multiplexer operation. When using the STCVDC for all cells (command 0x60), for each cell (CN) that is discharging, the adjacent lower cell (CN-1) will return a cell voltage value near 0V. To avoid misinterpretation of the cell voltages read after using this command, there are two recommendations: 1. Use the STCVDC command for all cell voltages (command 0x60) with only one discharge switch on at a time. The value returned for the cell directly below the cell being discharged will be invalid and read close to 0V. The voltage reading of all other cells, including the cell being discharged, will be valid. 2. Use the individual cell commands with discharge permitted (STCVDC commands 0x61 thru 0x6c) and only turn on the discharge switch for the cell being measured. The voltage reading for the individual cell being measured and discharged will be valid. All discharge switches are automatically disabled during OV and UV comparison measurements.
C4 B4 B3 CF4 CF3 C3 C2 C1 V- MUX
A/D CONVERTER DIGITAL SELF TEST
100A
68021 F03
Figure 3. Open Connection with RC Filtering
Two self test commands can be used to verify the functionality of the digital portions of the ADC. The self tests also verify the cell voltage registers and temperature monitoring registers. During these self tests a test signal is applied to the ADC. If the circuitry is working properly all cell voltage and temperature registers will contain
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LTC6802-1 OPERATION
identical codes. For Self Test 1 the registers will contain 0x555. For Self Test 2, the registers will contain 0xAAA. The time required for the self test function is the same as required to measure all cell voltages or all temperature sensors. Perform the self test function with CDC[2:0] set to 1 in the configuration register. USING THE S PINS AS DIGITAL OUTPUTS OR GATE DRIVERS The S outputs include an internal 10k pull-up resistor. Therefore the S pins will behave as a digital output when loaded with a high impedance, e.g. the gate of an external MOSFET. For applications requiring high battery discharge currents, connect a discrete PMOS switch device and suitable discharge resistor to the cell, and the gate terminal to the S output pin, as illustrated in Figure 4.
C(n) SI2351DS
Excessive heat results in elevated die temperatures. The electrical characteristics are guaranteed for die temperatures up to 85C. Little or no degradation will be observed in the measurement accuracy for die temperatures up to 105C. Damage may occur near 150C, therefore the recommended maximum die temperature is 125C. To protect the LTC6802-1 from damage due to overheating, a thermal shutdown circuit is included. Overheating of the device can occur when dissipating significant power in the cell discharge switches or when communicating frequently to the device using the current-mode serial interface. The problem is exacerbated when operating with a large voltage between V+ and V- or when the thermal conductivity of the system is poor. The thermal shutdown circuit is enabled whenever the device is not in standby mode (see Modes of Operation). For the LTC6802-1, the thermal shutdown circuit will also be enabled when any current mode input or output is sinking or sourcing current. If the temperature detected on the device goes above approximately 145C, the configuration registers will be reset to default states, turning off all discharge switches and disabling A/D conversions. Also, for the LTC6802-1, the current mode interface will not operate until the overtemperature condition goes away. When a thermal shutdown has occurred, the THSD bit in the temperature register group will go high. The bit is cleared by performing a read of the temperature registers (RDTMP command). Since thermal shutdown interrupts normal operation, the internal temperature monitor should be used to determine when the device temperature is approaching unacceptable levels.
15 1W VISHAY CRCW2512 SERIES
S(n)
C(n - 1)
68021 F04
Figure 4. External Discharge FET Connection (One Cell Shown)
POWER DISSIPATION AND THERMAL SHUTDOWN The MOSFETs connected to the pins S1 through S12 can be used to discharge battery cells. An external resistor should be used to limit the power dissipated by the MOSFETs. The maximum power dissipation in the MOSFETs is limited by the amount of heat that can be tolerated by the LTC6802-1.
APPLICATIONS INFORMATION
USING THE LTC6802-1 WITH LESS THAN 12 CELLS The LTC6802-1 can be used with as few as four cells. The minimum number of cells is governed by the supply voltage requirements of the LTC6802-1. The sum of the cell voltages must be 10V to guarantee that all electrical specifications are met. Figure 5 shows an example of the LTC6802-1 when used to monitor seven cells. The lowest C inputs connect to the seven cells and the upper C inputs connect to V+. Other configurations, e.g. 9 cells, would be configured in the same way: the lowest C inputs connected to the battery cells and the unused C inputs connected to V+. The unused inputs will result in a reading of 0V for those channels.
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LTC6802-1 APPLICATIONS INFORMATION
NEXT HIGHER GROUP OF 7 CELLS LTC6802-1 V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 C3 S3 C2 S2 C1 S1 V- NEXT LOWER GROUP OF 7 CELLS
68021 F05
The read back value of that bit will be the logic level that appears at the GPIO pin. When the MMB pin is low, the GPIO pins and the WDTB pin are treated as inputs that set the number of cells to be monitored. See the Monitor Mode section. WATCHDOG TIMER CIRCUIT The LTC6802-1 includes a watchdog timer circuit. If no activity is detected on the SCKI pin for 2 seconds, the WDTB open drain output is asserted low. The WDTB pin remains low until an edge is detected on the SCKI pin. When the watchdog timer circuit times out, the configuration bits are reset to their default (power-up) state. In the power-up state, the S outputs are off. Therefore, the watchdog timer provides a means to turn off cell discharging should communications to the MPU be interrupted. The IC is in the minimum power standby mode after a time out. Note that externally pulling the WDTB pin low will not reset the configuration bits. The configuration bit WDTEN (byte CNFG0, bit 7) allows the user to disable the watchdog timer operation. The default value is WDTEN = 1 (enabled). The watchdog timer operation is disabled when MMB is low. When reading the configuration register, byte CNFG0 bit 7 will reflect the state of the WDTB pin, independent of what value was written to the WDTEN bit. Consequently, if the watchdog timer is disabled by writing the WDTEN bit to 0, the WDTB pin can be used as a general purpose input, with the read value of the WDTEN bit reflecting an input applied to the WDTB pin. REVISION CODE The temperature register group contains a 3-bit revision code. If software detection of device revision is necessary, then contact the factory for details. Otherwise, the code can be ignored. In all cases, however, the values of all bits must be used when calculating the packet error code (PEC) CRC byte on data reads.
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Figure 5. Monitoring 7 Cells with the LTC6802-1
The ADC can also be commanded to measure a stack of cells by making 10 or 12 measurements, depending on the state of the CELL10 bit in the control register. Data from all 10 or 12 measurements must be down loaded when reading the conversion results. The ADC can be commanded to measure any individual cell voltage. USING THE GENERAL PURPOSE INPUTS/OUTPUTS (GPIO1, GPIO2) The LTC6802-1 has two general purpose digital inputs/outputs. By writing a GPIO configuration register bit to a logic low, the open drain output can be activated. The GPIOs give the user the ability to turn on/off circuitry around the LTC6802-1. One example might be a circuit to verify the operation of the system. When a GPIO configuration bit is written to a logic high, the corresponding GPIO pin may be used as an input.
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LTC6802-1 APPLICATIONS INFORMATION
MODES OF OPERATION The LTC6802-1 has three modes of operation: standby, measure, and monitor. Standby mode is a power saving state where all circuits except the serial interface are turned off. In measure mode, the LTC6802-1 is used to measure cell voltages and store the results in memory. Measure mode will also monitor each cell voltage for overvoltage (OV) and undervoltage (UV) conditions. In monitor mode, the device will only monitor cells for UV and OV conditions. A signal is output on the SDO pin to indicate the UV/OV status. The serial interface is disabled. Standby Mode The LTC6802-1 defaults (powers up) to standby mode. Standby mode is the lowest possible supply current state. All circuits are turned off except the serial interface and the voltage regulator. For the lowest possible standby current consumption all SPI logic inputs should be set to a logic 1 level. The LTC6802-1 can be programmed for standby mode by setting the comparator duty cycle configuration bits, CDC[2:0], to 0. If the part is put into standby mode while ADC measurements are in progress, the measurements will be interrupted and the cell voltage registers will be in an indeterminate state. To exit standby mode, the CDC bits must be written to a value other than 0. Measure Mode LTC6802-1 is in measure mode when the CDC bits are programmed with a value from 1 to 7. The IC monitors each cell voltage and produces an interrupt signal on the SDO pin indicating all cell voltages are within the UV and OV limits. There are two methods for indicating the UV/OV interrupt status: toggle polling (using a 1kHz output signal) and level polling (using a high or low output signal). The polling methods are described in the Serial Port section. The UV/OV limits are set by the VUV and VOV values in the configuration registers. When a cell voltage exceeds the UV/OV limits a bit is set in the flag register. The UV and OV flag status for each cell can be determined using the Read Flag Register Group. If fewer than 12 cells are connected to the LTC6802-1 then it is necessary to mask the unused input channels. The MCxI bits in the configuration registers are used to mask channels. If the CELL10 bit is high, then the inputs for cells 11 and 12 are automatically masked. The LTC6802-1 can monitor UV and OV conditions continuously. Alternatively, the duty cycle of the UV and OV comparisons can be reduced or turned off to lower the overall power consumption. The CDC bits are used to control the duty cycle. To initiate cell voltage measurements while in measure mode, a Start A/D Conversion and Poll Status command must be sent. After the command has been sent, the LTC6802-1 will send the A/D converter status using either the toggle polling or the level polling method, as described in the Serial Port section. If the CELL10 bit is high, then only the bottom 10 cell voltages will be measured, thereby reducing power consumption and measurement time. By default the CELL10 bit is low, enabling measurement of all 12 cell voltages. During cell voltage measurement commands, UV and OV flag conditions, reflected in the flag register group, are also updated. When the measurements are complete, the part will go back to monitoring UV and OV conditions at the rate designated by the CDC bits. Monitor Mode The LTC6802-1 can be used as a simple monitoring circuit with no serial interface by pulling the MMB pin low. When in this mode, the interrupt status is indicated on the SDO pin using the toggle polling mode described in the Serial Port section. Unlike serial port polling commands, however, the toggling is independent of the state of the CSBI pin. See Figure 6. When the MMB pin is low, all the device configuration values are reset to the default states shown in Table 12. When MMB is held low the VUV, VOV, and CDC register values are ignored. Instead VUV and VOV use factoryprogrammed setings. CDC is set to state 5. The number of cells to be monitored is set by the logic levels on the WDTB and GPIO pins, as shown in Table 1.
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LTC6802-1 APPLICATIONS INFORMATION
LTC6802-1 CSBI SDO SDI SCKI VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3 CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 BATTERY POSITIVE 350V CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 LTC6802-1 IC #8 CSBI SDO SDI SCKI
VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
IC #3 TO IC #7
LTC6802-1 CSBI SDO SDI SCKI VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3 CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4
LTC6802-1 IC #2
CSBI SDO SDI SCKI
VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
3V V2- OE2 CSBI SDO SDI SCKI V2+ V2- V1- V1+ V1- OE1 MPU CS MISO MOSI CLK MODULE IO
LTC6802-1 CSBI SDO SDI SCKI VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3 CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4
LTC6802-1 IC #1
VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
DIGITAL ISOLATOR
3V
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Figure 6. Redundant Monitoring Circuit
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LTC6802-1 APPLICATIONS INFORMATION
Table 1. Monitor Mode Cell Selection
WDTB 0 0 0 0 1 1 1 1 GPIO2 0 0 1 1 0 0 1 1 GPIO1 0 1 0 1 0 1 0 1 CELL INPUTS MONITORED Cells 1 to 5 Cells 1 to 6 Cells 1 to 7 Cells 1 to 8 Cells 1 to 9 Cells 1 to 10 Cells 1 to 11 Cells 1 to 12
are always outputs that can drive the next higher device in a stack. SDI is a data input when writing to a stack of devices. For devices not at the bottom of a stack, SDI is a data output when reading from the stack. SDOI is a data output when writing to and a data input when reading from a stack of devices. SDO is an open drain output that is only used on the bottom device of a stack, where it may be tied with SDI, if desired, to form a single, bi-directional port. The SDO pin on the bottom device of a stack requires a pull-up resistor. For devices up in the stack, SDO should be tied to the local V- or left floating. To communicate between daisy-chained devices, the high side port pins of a lower device (CSBO, SCKO, and SDOI) must be connected through PN junction diodes to the respective low side port pins of the next higher device (CSBI, SCKI, and SDI). In this configuration, the devices communicate using current rather than voltage. To signal a logic high from the lower device to the higher device, the lower device sinks a smaller current from the higher device pin. To signal a logic low, the lower device sinks a larger current. Likewise, to signal a logic high from the higher device to the lower device, the higher device sources a larger current to the lower device pin. To signal a logic low, the higher device sources a smaller current. See Figure 7. Standby current consumed in the current mode serial interface is minimized when CSBI, SCKI, and SDI are all high.
If MMB is low then brought high, all device configuration values are reset to the default states including the VUV, VOV, and CDC configuration bits. SERIAL PORT Overview The LTC6802-1 has an SPI bus compatible serial port. Several devices can be daisy chained in series. There are two sets of serial port pins, designated as low side and high side. The low side and high side ports enable devices to be daisy chained even when they operate at different power supply potentials. In a typical configuration, the positive power supply of the first, bottom device is connected to the negative power supply of the second, top device, as shown in Figure 1. When devices are stacked in this manner, they can be daisy chained by connecting the high side port of the bottom device to the low side port of the top device. With this arrangement, the master writes to or reads from the cascaded devices as if they formed one long shift register. The LTC6802-1 translates the voltage level of the signals between the low side and high side ports to pass data up and down the battery stack. Physical Layer On the LTC6802-1, seven pins comprise the low side and high side ports. The low side pins are CSBI, SCKI, SDI, and SDO. The high side pins are CSBO, SCKO and SDOI. CSBI and SCKI are always inputs, driven by the master or by the next lower device in a stack. CSBO and SCKO
VSENSE (WRITE)
+ -
LOW SIDE PORT ON HIGHER DEVICE
READ 1
WRITE
HIGH SIDE PORT ON LOWER DEVICE
VSENSE (READ)
+ -
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Figure 7. Current Mode Interface
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LTC6802-1 APPLICATIONS INFORMATION
The voltage mode pin (VMODE) determines whether the low side serial port is configured as voltage mode or current mode. For the bottom device in a daisy-chain stack, this pin must be pulled high (tied to VREG). The other devices in the daisy chain must have this pin pulled low (tied to V-) to designate current mode communication. To designate the top-of-stack device for polling commands, the TOS pin on the top device of a daisy chain must be tied high. The other devices in the stack must have TOS tied low. See Figure 1. Data Link Layer Clock Phase And Polarity: The LTC6802-1 SPI-compatible interface is configured to operate in a system using CPHA=1 and CPOL=1. Consequently, data on SDI must be stable during the rising edge of SCKI. Data Transfers: Every byte consists of 8 bits. Bytes are transferred with the most significant bit (MSB) first. On a write, the data value on SDI is latched into the device on the rising edge of SCKI (Figure 8). Similarly, on a read, the data value output on SDO is valid during the rising edge of SCKI and transitions on the falling edge of SCKI (Figure 9). CSBI must remain low for the entire duration of a command sequence, including between a command byte and subsequent data. On a write command, data is latched in on the rising edge of CSBI. After a polling command has been entered, the SDO output will immediately be driven by the polling state, with the SCKI input ignored (Figure 10). See the Toggle Polling and Level Polling sections.
CSBI
SCKI
SDI
MSB (CMD)
BIT6 (CMD)
LSB (CMD)
MSB (DATA)
LSB (DATA)
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Figure 8. Transmission Format (Write)
CSBI
SCKI
SDI
MSB (CMD)
BIT6 (CMD)
LSB (CMD)
SDO
MSB (DATA)
LSB (DATA)
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Figure 9. Transmission Format (Read)
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LTC6802-1 APPLICATIONS INFORMATION
CSBI
SCKI
SDI
MSB (CMD)
BIT6 (CMD)
LSB (CMD)
SDO
POLL STATE
68021 F10
Figure 10. Transmission Format (Poll)
Network Layer Broadcast Commands: A broadcast command is one to which all devices on the bus will respond, regardless of device address. See the Bus Protocols and Commands sections. In daisy chained configurations, all devices in the chain receive the command bytes simultaneously. For example, to initiate A/D conversions in a stack of devices, a single STCVAD command byte is sent, and all devices will start conversions at the same time. For read and write commands, a single command byte is sent, and then the stacked devices effectively turn into a cascaded shift register, in which data is shifted through each device to the next higher (on a write) or the next lower (on a read) device in the stack. See the Serial Command Examples section. PEC Byte: The Packet Error Code (PEC) byte is a CRC value calculated for all of the bits in a register group in the order they are read, using the following characteristic polynomial: x8 + x2 + x + 1 On a read command, after sending the last byte of a register group, the device will shift out the calculated PEC, MSB first. For daisy-chained devices, after the PEC is read from the first device, the data from any daisy-chained devices will follow in the same order. For example, when reading the flag registers from two stacked devices (bottom
device A and top device B), the data will be output in the following order: FLGR0(A), FLGR1(A), FLGR2(A), PEC(A), FLGR0(B), FLGR1(B), FLGR2(B), PEC(B) Toggle Polling: Toggle polling allows a robust determination both of device states and of the integrity of the connections between the devices in a stack. Toggle polling is enabled when the LVLPL bit is low. After entering a polling command, the data out line will be driven by the slave devices based on their status. When polling for the A/D converter status, data out will be low when any device is busy performing an A/D conversion and will toggle at 1kHz when no device is busy. Similarly, when polling for interrupt status, the output will be low when any device has an interrupt condition and will toggle at 1kHz when none has an interrupt condition. Toggle Polling--Daisy-Chained Broadcast Polling: The SDO pin (bottom device) or SDI pin (stacked devices) will be low if a device is busy/in interrupt. If it is not busy/not in interrupt, the device will pass the signal from the SDOI input to data out (if not the top-of-stack device) or toggle the data out line at 1kHz (if the top-of-stack device). The master pulls CSBI high to exit polling. Level polling: Level polling is enabled when the LVLPL bit is high. After entering a polling command, the data out line will be driven by the slave devices based on their status. When polling for the A/D converter status, data
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LTC6802-1 APPLICATIONS INFORMATION
out will be low when any device is busy performing an A/D conversion and will be high when no device is busy. Similarly, when polling for interrupt status, the output will be low when any device has an interrupt condition and will be high when none has an interrupt condition. Level polling--Daisy-Chained Broadcast Polling: The SDO pin (bottom device) or SDI pin (stacked devices) will be low if a device is busy/in interrupt. If it is not busy/not in interrupt, the device will pass the level from the SDOI input to data out (if not the top-of-stack device) or hold the data out line high (if the top-of-stack device). Therefore, if any device in the chain is busy or in interrupt, the SDO signal at the bottom of the stack will be low. If all devices are not busy/not in interrupt, the SDO signal at the bottom of the stack will be high. The master pulls CSBI high to exit polling. Polling Methods: For A/D conversions, three methods can be used to determine A/D completion. First, a controller can start an A/D conversion and wait for the specified
Table 2. Protocol Key
PEC N ... Packet error code (CRC-8) Number of bits Continuation of protocol Master-to-slave Slave-to-master Complete byte of data
conversion time to pass before reading the results. The second method is to hold CSBI low after an A/D start command has been sent. The A/D conversion status will be output on SDO. A problem with the second method is that the controller is not free to do other serial communication while waiting for A/D conversions to complete. The third method overcomes this limitation. The controller can send an A/D start command, perform other tasks, and then send a Poll A/D Converter Status (PLADC) command to determine the status of the A/D conversions. For OV/UV interrupt status, the Poll Interrupt Status (PLINT) command can be used to quickly determine whether any cell in a stack is in an overvoltage or undervoltage condition. Bus Protocols There are 3 different protocol formats, depicted in Table 3 through Table 5. Table 2 is the key for reading the protocol diagrams.
Table 3. Broadcast Poll Command
8 Command Poll Data
Table 4. Broadcast Read
8 Command 8 Data Byte Low ... 8 Data Byte High 8 PEC 8 Shift Byte 1 ... 8 Shift Byte N
Table 5. Broadcast Write
8 Command 8 Data Byte Low ... 8 Data Byte High 8 Shift Byte 1 ... 8 Shift Byte N
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LTC6802-1 APPLICATIONS INFORMATION
Commands
Table 6. Command Codes
Write Configuration Register Group Read Configuration Register Group Read Cell Voltage Register Group Read Flag Register Group Read Temperature Register Group Start Cell Voltage A/D Conversions and Poll Status WRCFG RDCFG RDCV RDFLG RDTMP STCVAD 0x01 0x02 0x04 0x06 0x08 0x10 (all cell voltage inputs) 0x11 (cell 1 only) 0x12 (cell 2 only) ... 0x1A (cell 10 only) 0x1B (cell 11 only, if CELL10 bit=0) 0x1C (cell 12 only, if CELL10 bit=0) 0x1D (unused) 0x1E (cell self test 1; all CV=0x555) 0x1F (cell self test 2; all CV=0xAAA) 0x20 (all cell voltage inputs) 0x21 (cell 1 only) 0x22 (cell 2 only) ... 0x2A (cell 10 only) 0x2B (cell 11 only, if CELL10 bit=0) 0x2C (cell 12 only, if CELL10 bit=0) 0x2D (unused) 0x2E (cell self test 1; all CV=0x555) 0x2F (cell self test 2; all CV=0xAAA) 0x30 (all temperature inputs) 0x31 (external temp 1 only) 0x32 (external temp 1 only) 0x33 (internal temp only) 0x34--0x3D (unused) 0x3E (temp self test 1; all TMP=0x555) 0x3F (temp self test 2; all TMP=0xAAA) 0x40 0x50 0x60 (all cell voltage inputs) 0x61 (cell 1 only) 0x62 (cell 2 only) ... 0x6A (cell 10 only) 0x6B (cell 11 only, if CELL10 bit=0) 0x6C (cell 12 only, if CELL10 bit=0) 0x6D (unused) 0x6E (cell self test 1; all CV=0x555) 0x6F (cell self test 2; all CV=0xAAA) 0x70 (all cell voltage inputs) 0x71 (cell 1 only) 0x72 (cell 2 only) ... 0x7A (cell 10 only) 0x7B (cell 11 only, if CELL10 bit=0) 0x7C (cell 12 only, if CELL10 bit=0) 0x7D (unused) 0x7E (cell self test 1; all CV=0x555) 0x7F (cell self test 2; all CV=0xAAA)
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Start Open Wire A/D Conversions and Poll Status
STOWAD
Start Temperature A/D Conversions and Poll Status
STTMPAD
Poll A/D Converter Status Poll Interrupt Status Start Cell Voltage A/D Conversions and Poll Status, with Discharge Permitted
PLADC PLINT STCVDC
Start Open Wire A/D Conversions and Poll Status, with Discharge Permitted
STOWDC
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LTC6802-1 APPLICATIONS INFORMATION
Memory Map Table 7 through Table 12 show the memory map for the LTC6802-1. Table 12 gives bit descriptions.
Table 7. Configuration (CFG) Register Group
REGISTER CFGR0 CFGR1 CFGR2 CFGR3 CFGR4 CFGR5 RD/WR RD/WR RD/WR RD/WR RD/WR RD/WR RD/WR BIT 7 WDTEN DCC8 MC4I MC12I VUV[7] VOV[7] BIT 6 GPIO2 DCC7 MC3I MC11I VUV[6] VOV[6] BIT 5 GPIO1 DCC6 MC2I MC10I VUV[5] VOV[5] BIT 4 LVLPL DCC5 MC1I MC9I VUV[4] VOV[4] BIT 3 CELL10 DCC4 DCC12 MC8I VUV[3] VOV[3] BIT 2 CDC[2] DCC3 DCC11 MC7I VUV[2] VOV[2] BIT 1 CDC[1] DCC2 DCC10 MC6I VUV[1] VOV[1] BIT 0 CDC[0] DCC1 DCC9 MC5I VUV[0] VOV[0]
Table 8. Cell Voltage (CV) Register Group
REGISTER CVR00 CVR01 CVR02 CVR03 CVR04 CVR05 CVR06 CVR07 CVR08 CVR09 CVR10 CVR11 CVR12 CVR13 CVR14 CVR15* CVR16* CVR17* RD/WR RD RD RD RD RD RD RD RD RD RD RD RD RD RD RD RD RD RD BIT 7 C1V[7] C2V[3] C2V[11] C3V[7] C4V[3] C4V[11] C5V[7] C6V[3] C6V[11] C7V[7] C8V[3] C8V[11] C9V[7] C10V[3] C10V[11] C11V[7] C12V[3] C12V[11] BIT 6 C1V[6] C2V[2] C2V[10] C3V[6] C4V[2] C4V[10] C5V[6] C6V[2] C6V[10] C7V[6] C8V[2] C8V[10] C9V[6] C10V[2] C10V[10] C11V[6] C12V[2] C12V[10] BIT 5 C1V[5] C2V[1] C2V[9] C3V[5] C4V[1] C4V[9] C5V[5] C6V[1] C6V[9] C7V[5] C8V[1] C8V[9] C9V[5] C10V[1] C10V[9] C11V[5] C12V[1] C12V[9] BIT 4 C1V[4] C2V[0] C2V[8] C3V[4] C4V[0] C4V[8] C5V[4] C6V[0] C6V[8] C7V[4] C8V[0] C8V[8] C9V[4] C10V[0] C10V[8] C11V[4] C12V[0] C12V[8] BIT 3 C1V[3] C1V[11] C2V[7] C3V[3] C3V[11] C4V[7] C5V[3] C5V[11] C6V[7] C7V[3] C7V[11] C8V[7] C9V[3] C9V[11] C10V[7] C11V[3] C11V[11] C12V[7] BIT 2 C1V[2] C1V[10] C2V[6] C3V[2] C3V[10] C4V[6] C5V[2] C5V[10] C6V[6] C7V[2] C7V[10] C8V[6] C9V[2] C9V[10] C10V[6] C11V[2] C11V[10] C12V[6] BIT 1 C1V[1] C1V[9] C2V[5] C3V[1] C3V[9] C4V[5] C5V[1] C5V[9] C6V[5] C7V[1] C7V[9] C8V[5] C9V[1] C9V[9] C10V[5] C11V[1] C11V[9] C12V[5] BIT 0 C1V[0] C1V[8] C2V[4] C3V[0] C3V[8] C4V[4] C5V[0] C5V[8] C6V[4] C7V[0] C7V[8] C8V[4] C9V[0] C9V[8] C10V[4] C11V[0] C11V[8] C12V[4]
*Registers CVR15, CVR16, and CVR17 can only be read if the CELL10 bit in register CFGR0 is low
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LTC6802-1 APPLICATIONS INFORMATION
Table 9. Flag (FLG) Register Group
REGISTER FLGR0 FLGR1 FLGR2 RD/WR RD RD RD BIT 7 C4OV C8OV C12OV* BIT 6 C4UV C8UV C12UV* BIT 5 C3OV C7OV C11OV* BIT 4 C3UV C7UV C11UV* BIT 3 C2OV C6OV C10OV BIT 2 C2UV C6UV C10UV BIT 1 C1OV C5OV C9OV BIT 0 C1UV C5UV C9UV
* Bits C11UV, C12UV, C11OV, and C12OV are always low if the CELL10 bit in register CFGR0 is high
Table 10. Temperature (TMP) Register Group
REGISTER TMPR0 TMPR1 TMPR2 TMPR3 TMPR4 RD/WR RD RD RD RD RD BIT 7 ETMP1[7] ETMP2[3] ETMP2[11] ITMP[7] REV[2] BIT 6 ETMP1[6] ETMP2[2] ETMP2[10] ITMP[6] REV[1] BIT 5 ETMP1[5] ETMP2[1] ETMP2[9] ITMP[5] REV[0] BIT 4 ETMP1[4] ETMP2[0] ETMP2[8] ITMP[4] THSD BIT 3 ETMP1[3] ETMP1[11] ETMP2[7] ITMP[3] ITMP[11] BIT 2 ETMP1[2] ETMP1[10] ETMP2[6] ITMP[2] ITMP[10] BIT 1 ETMP1[1] ETMP1[9] ETMP2[5] ITMP[1] ITMP[9] BIT 0 ETMP1[0] ETMP1[8] ETMP2[4] ITMP[0] ITMP[8]
Table 11. Packet Error Code (PEC)
REGISTER PEC RD/WR RD BIT 7 PEC[7] BIT 6 PEC[6] BIT 5 PEC[5] BIT 4 PEC[4] BIT 3 PEC[3] BIT 2 PEC[2] BIT 1 PEC[1] BIT 0 PEC[0]
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LTC6802-1 APPLICATIONS INFORMATION
Table 12. Memory Bit Descriptions
NAME DESCRIPTION VALUES CDC 0 (default) 1 2 CDC Comparator Duty Cycle 3 4 5* 6 7 CELL10 LVLPL GPIO1 GPIO2 WDTEN DCCx VUV VOV MCxI CxV CxUV CxOV ETMPx THSD REV ITMP PEC 10-Cell Mode Level Polling Mode GPIO1 Pin Control GPIO2 Pin Control Watchdog Timer Enable Discharge Cell x Undervoltage Comparison Voltage* Overvoltage Comparison Voltage* Mask Cell x Interrupts Cell x Voltage* Cell x Undervoltage Flag Cell x Overvoltage Flag External Temperature Measurement* Thermal Shutdown Status Revision Code Internal Temperature Measurement* Packet Error Code x=1..12 x=1..12 UV/OV COMPARATOR PERIOD N/A (Comparator Off) Standby Mode N/A (Comparator Off) 13ms 130ms 500ms 130ms 500ms 2000ms VREF POWERED DOWN BETWEEN MEASUREMENTS Yes No No No No Yes Yes Yes CELL VOLTAGE MEASUREMENT TIME N/A 13ms 13ms 13ms 13ms 21ms 21ms 21ms
*when MMB pin is low, the CDC value is set to 5 0=12-cell mode (default); 1=10-cell mode 0=toggle polling (default); 1=level polling Write: 0=GPIO1 pin pull down on; 1=GPIO1 pin pull down off (default) Read: 0=GPIO1 pin at logic `0'; 1=GPIO1 pin at logic `1' Write: 0=GPIO2 pin pull down on; 1=GPIO2 pin pull down off (default) Read: 0=GPIO2 pin at logic `0'; 1=GPIO2 pin at logic `1' Write: 0=watchdog timer disabled; 1=watchdog timer enabled (default) Read: 0=WDTB pin at logic `0'; 1=WDTB pin at logic `1' x=1..12 0=turn off shorting switch for cell `x' (default); 1=turn on shorting switch Comparison voltage = VUV * 16 * 1.5mV (default VUV=0. When MMB pin is low a factory programmed comparison voltage is used) Comparison voltage = VOV * 16 * 1.5mV (default VOV=0. When MMB pin is low a factory programmed comparison voltage is used) x=1..12 x=1..12 0=enable interrupts for cell `x' (default) 1=turn off interrupts and clear flags for cell `x' 12-bit ADC measurement value for cell `x' cell voltage for cell `x' = CxV * 1.5mV reads as 0xFFF while A/D conversion in progress cell voltage compared to VUV comparison voltage 0=cell `x' not flagged for under voltage condition; 1=cell `x' flagged cell voltage compared to VOV comparison voltage 0=cell `x' not flagged for over voltage condition; 1=cell `x' flagged
Temperature measurement voltage = ETMPx * 1.5mV 0= thermal shutdown has not occurred; 1=thermal shutdown has occurred Status cleared to `0' on read of Thermal Register Group Device revision code Temperature measurement voltage = ITMP * 1.5mV = 8mV * T(K) CRC value for reads
*Voltage determinations use the decimal value of the registers, 0 to 4095 for 12-bit and 0 to 255 for 8-bit registers
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LTC6802-1 APPLICATIONS INFORMATION
SERIAL COMMAND EXAMPLES LTC6802-1 (Daisy Chained Configuration) Examples below use a configuration of three stacked devices: bottom (B), middle (M), and top (T) Write Configuration Registers 1. 2. 3. 4. 5. 6. Pull CSBI low Send WRCFG command byte Send CFGR0 byte for top device, then CFGR1 (T), CFGR2 (T), ... CFGR5 (T) Send CFGR0 byte for middle device, then CFGR1 (M), CFGR2 (M), ... CFGR5 (M) Send CFGR0 byte for bottom device, then CFGR1 (B), CFGR2 (B), ... CFGR5 (B) Pull CSBI high; data latched into all devices on rising edge of CSBI
Calculation of serial interface time for sequence above: Number of devices in stack= N Number of bytes in sequence = B = 1 command byte and 6 data bytes per device = 1+6*N Serial port frequency per bit = F Time = (1/F) * B * 8 bits/byte = (1/F) * (1+6*N) * 8 Time for 3-cell example above, with 1MHz serial port = (1/1000000) * (1+6*3)*8 = 152us Read Cell Voltage Registers (12 Cell Mode) 1. 2. 3. 4. 5. 6. Pull CSBI low Send RDCV command byte Read CVR00 byte of bottom device, then CVR01 (B), CVR02 (B), ... CVR17 (B), and then PEC (B) Read CVR00 byte of middle device, then CVR01 (M), CVR02 (M), ... CVR17 (M), and then PEC (M) Read CVR00 byte for top device, then CVR01 (T), CVR02 (T), ... CVR17 (T), and then PEC (T) Pull CSBI high
Calculation of serial interface time for sequence above: Number of devices in stack= N Number of bytes in sequence = B = 1 command byte, and 18 data bytes plus 1 PEC byte per device = 1+19*N Serial port frequency per bit = F Time = (1/F) * B * 8 bits/byte = (1/F) * (1+19*N) * 8 Time for 3-cell example above, with 1MHz serial port = (1/1000000) * (1+19*3)*8 =464us Start Cell Voltage A/D Conversions and Poll Status (Toggle Polling) 1. 2. 3. 4. 5. Pull CSBI low Send STCVAD command byte (all devices in stack start A/D conversions simultaneously) SDO output from bottom device pulled low for approximately 12ms SDO output toggles at 1kHz rate, indicating conversions complete for all devices in daisy chain Pull CSBI high to exit polling
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LTC6802-1 APPLICATIONS INFORMATION
Poll Interrupt Status (Level Polling) 1. 2. 3. 4. Pull CSBI low Send PLINT command byte SDO output from bottom device pulled low if any device has an interrupt condition; otherwise, SDO high Pull CSBI high to exit polling assembly and service procedures that might affect a battery system during its useful lifespan. Table 13 shows the various situations that should be considered when planning protection circuitry. The first five scenarios are to be anticipated during production and appropriate protection is included within the LTC6802-1 device itself.
FAULT PROTECTION Overview Care should always be taken when using high energy sources such as batteries. There are numerous ways that systems can be [mis-]configured when considering the
Table 13. LTC6802-1 Failure Mechanism Effect Analysis
SCENARIO Cell input open-circuit (random) Cell input open-circuit (random) EFFECT Power-up sequence at IC inputs Differential input voltage overstress
DESIGN MITIGATION Clamp diodes at each pin to V+ & V- (within IC) provide alternate power-path. Zener diodes across each cell voltage input pair (within IC) limits stress. Clamp diodes at each pin to V+ & V- (within IC) provide alternate power-path. Diode conduction at data ports will impair communication with higher-potential units.
Top cell input connection loss (V+) Power will come from highest connected cell input or via data port fault current Bottom cell input connection loss (V-)
Power will come from lowest connected cell input or Clamp diodes at each pin to V+ & V- (within IC) provide alternate power-path. Diode conduction at data ports will impair via data port fault current communication with higher-potential units. Clamp diodes at each pin to V+ & V- (within IC) provide an alternate power-path if there are other devices (which can supply power) connected to the LTC6802-1. Diode conduction at data ports will impair communication with higher-potential units. If the watchdog timer is enabled, all units above the disconnection will enter standby mode within 2 seconds of disconnect. Discharge switches are disabled in standby mode.
Disconnection of a harness Loss of supply connection to the IC between a group of battery cells and the IC (in a system of stacked groups) Data link disconnection between stacked LTC6802-1 units. Break of "daisy chain" communication (no stress to ICs). Communication will be lost to devices above the disconnection. The devices below the disconnection are still able to communicate and perform all functions, however, the polling feature is disabled.
Cell-pack integrity, break between stacked units Cell-pack integrity, break between stacked units Cell-pack integrity, break within stacked unit Cell-pack integrity, break within stacked unit
Daisy-chain voltage reversal up to full stack potential Use series protection diodes with top-port I/O connections during pack discharge (RS07J for up to 600V). Use isolated data link at bottom-most data port. Daisy-chain positive overstress during charging Cell input reverse overstress during discharge Add redundant current path link Add parallel Schottky diodes across each cell for load-path redundancy. Diode and connections must handle full operating current of stack, will limit stress on IC Add SCR across each cell for charge-path redundancy. SCR and connections must handle full charging current of stack, will limit stress on IC by selection of trigger Zener
Cell input positive overstress during charge
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LTC6802-1 APPLICATIONS INFORMATION
Battery Interconnection Integrity The FMEA scenarios involving a break in the stack of battery cells are potentially the most damaging. In the case where the battery stack has a discontinuity between groupings of cells monitored by LTC6802-1 ICs, any load will force a large reverse potential on the daisy-chain connection. This situation might occur in a modular battery system during initial installation or a service procedure. The daisy chain ports are protected from the reverse potential in this scenario by external series high-voltage diodes required in the upper-port data connections as shown in Figure 11. During the charging phase of operation, this fault would lead to forward biasing of daisy-chain ESD clamps that would also lead to part damage. An alternative connection to carry current during this scenario will avoid this stress from being applied (Figure 11).
LTC6802-1 (NEXT HIGHER IN STACK) SDO PROTECT AGAINST BREAK HERE OPTIONAL REDUNDANT CURRENT PATH V+ SDI SCKI CSBI RS07J (3x) SDOI SCKO CSBO LTC6802-1 (NEXT LOWER IN STACK)
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unpredictable voltage clamping or current flow. Limiting the current flow at any pin to 10mA will prevent damage to the IC.
LTC6802-1 V+ SCKO C12 S12 SDOI C11 S11 ZCLAMP C10 S10 C9 S9 C8 S8 C7 S7 ZCLAMP C6 S6 C5 S5 C4 S4 C3 S3 ZCLAMP C2 S2 C1 GPIO2 GPIO1 WDTB MMB TOS
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CSBO
V
-
CSBI SDO SDI SCKI VMODE
Figure 11. Reverse-Voltage Protection for the Daisy-Chain (One Link Connection Shown)
Internal Protection Diodes Each pin of the LTC6802-1 has protection diodes to help prevent damage to the internal device structures caused by external application of voltages beyond the supply rails as shown in Figure 12. The diodes shown are conventional silicon diodes with a forward breakdown voltage of 0.5V. The unlabeled zener diode structures have a reverse breakdown characteristic which initially breaks down at 12V then snaps back to a 7V clamping potential. The zener diodes labeled ZCLAMP are higher voltage devices with an initial reverse breakdown of 30V snapping back to 25V. The forward voltage drop of all zeners is 0.5V. Refer to this diagram in the event of
S1 V
-
Figure 12. Internal Protection Diodes
Cell-Voltage Filtering The LTC6802-1 employs a sampling system to perform its analog-to-digital conversions and provides a conversion result that is essentially an average over the 0.5ms conversion window, provided there isn't noise aliasing with respect to the delta-sigma modulator rate of 512kHz. This indicates that a lowpass filter with useful attenuation at
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LTC6802-1 APPLICATIONS INFORMATION
500kHz may be beneficial. Since the delta-sigma integration bandwidth is about 1kHz, the filter corner need not be lower than this to assure accurate conversions. Series resistors of 100 may be inserted in the input paths without introducing meaningful measurement error, provided only external discharge switch FETs are being used. Shunt capacitors may be added from the cell inputs to V-, creating RC filtering as shown in Figure 13. Note that this filtering is not compatible with use of the internal discharge switches to carry current since this would induce settling errors at the time of conversion as any activated switches temporarily open to provide Kelvin mode cell sensing. As a discharge switch opens, cell wiring resistance will also form a small voltage step (recovery of the small IR drop), so keeping the frequency cutoff of the filter relatively high will allow adequate settling prior to the actual conversion. A guard time of about 60s is provided in the ADC timing, so a 16kHz LP is optimal and offers about 30dB of noise rejection. No resistor should be placed in series with the V- pin. Because the supply current flows from the V- pin, any resistance on this pin could generate a significant conversion error for CELL1.
C(n) 100 100nF LTC6802-1 S(n) C(n - 1) 100 100nF
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LTC6802-1 VREG VREF VTEMP2 VTEMP1 NC V-
100k
100k
1F 1F
100k NTC 100k NTC
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Figure 14. Driving Thermistors Directly from VREF
For sensors that require higher drive currents, a buffer op amp may be used as shown in Figure 15. Power for the sensor is actually sourced indirectly from the VREG pin in this case. Probe loads up to about 1mA maximum are supported in this configuration. Since VREF is shutdown during the LTC6802-1 idle and shutdown modes, the thermistor drive is also shut off and thus power dissipation minimized. Since VREG remains always on, the buffer op amp (LT6000 shown) is selected for its ultralow power consumption (10A).
+
LTC6000
-
VREG VREF VTEMP2 VTEMP1 NC V-
10k
10k
10k NTC 10k NTC
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Figure 13. Adding RC Filtering to the Cell Inputs (One Cell Connection Shown)
READING EXTERNAL TEMPERATURE PROBES Using Dedicated Inputs The LTC6802-1 includes two channels of ADC input, VTEMP1 and VTEMP2, that are intended to monitor thermistors (tempco about -4%/C generally) or diodes (-2.2mV/C typical) located within the cell array. Sensors can be powered directly from VREF as shown in Figure 14 (up to 60A total).
Figure 15. Buffering VREF for Higher-Current Sensors
Expanding Probe Count The LTC6802-1 provides general purpose I/O pins, GPIO1 and GPIO2, that may be used to control multiplexing of several temperature probes. Using just one of the GPIO pins, the sensor count can double to four as shown in
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LTC6802-1 APPLICATIONS INFORMATION
Figure 16. Using both GPIO pins, up to eight sensor inputs can be supported. Another method of multiple sensor support is possible without the use of any GPIO pins. If the sensors are PN diodes and several used in parallel, then the hottest diode will produce the lowest forward voltage and effectively establish the input signal to the VTEMP input(s). The hottest diode will therefore dominate the readout from the VTEMP inputs that the diodes are connected to. In this scenario, the specific location or distribution of heat is not known, but such information may not be important in practice. Figure 17 shows the basic concept. In any of the sensor configurations shown, a full-scale cold readout would be an indication of a failed-open sensor connection to the LTC6802-1.
LTC6802-1 GPIO1 100k 100k 100k NTC 100k NTC 1F 100k NTC
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ADDING CALIBRATION AND FULL-STACK MEASUREMENTS By adding multiplexing hardware, additional signals can be digitized by the CELL1 ADC channel. One useful signal to provide is a high-accuracy voltage reference, such as from an LT1461A-4. By periodic readings of this signal, host software can provide correction of the LTC6802-1 readings to improve the accuracy over that of the internal LTC6802-1 reference, and/or validate ADC operation. Another useful signal is a measure of the total stack potential. This provides a redundant operational measurement of the cells in the event of a malfunction in the normal acquisition process, or as a faster means of monitoring the entire stack potential. Figure 18 shows a means of providing both of these features. A resistor divider is used to provide a low-voltage representation of the full stack potential (C12 to C0 voltage) with MOSFETs that decouple the divider current under unneeded conditions. Other MOSFETs, in conjunction with an op amp having a shutdown mode, form a voltage selector that allows measurement of the normal cell1 potential (when GPIO1 is low) or a buffered MUX signal. When the MUX is active (GPIO1 is high), selection can be made between the reference (4.096V) or the full-stack voltage divider (GPOI2 set low will select the reference). During idle time when the LTC6802-1 WTB signal goes low, the external circuitry goes into a power down condition, reducing battery drain to a minimum. When not actively performing measurements, GPIO1 should be set low and GPIO2 should be set high to achieve the lowest power state for the configuration shown. PROVIDING HIGH-SPEED OPTO-ISOLATION OF THE SPI DATA-PORT Isolation techniques that are capable of supporting the 1Mbps data rate of the LTC6802-1 require more power on the isolated (battery) side than can be furnished by the VREG output of the LTC6802-1. To keep battery drain minimal, this means that a DC/DC function must be implemented along with a suitable data isolation circuit, such as shown in Figure 19. Here an optimal Avago 4-channel (3/1 bidirectional) opto-coupler is used, with a simple isolated supply generated by an LTC1693-2 configured as a 200kHz oscillator. The DC/DC function provides an unregulated
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SN74LVC1G3157 OR SIMILAR DEVICE
VREG VREF VTEMP2 VTEMP1 NC V-
100k
100k NTC
Figure 16. Expanding Sensor Count with Multiplexing
200k LTC6802-1 VREG VREF VTEMP2 VTEMP1 NC V- 200k
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Figure 17. Using Diode Sensors as Hot-Spot Detectors
27
LTC6802-1 APPLICATIONS INFORMATION
CELL12 2.2M GPIO2 GPIO1 WDTB 1M 1M VREG 2N7002 LTC6802-1 V- C1 150 TP0610K TP0610K 100 100nF 1F 2N7002 90.9k 1M 10M 0 = REF_EN 0 = CELL1 VSTACK12 LT1461A-4 DNC DNC VIN DNC SD VOUT GND DNC TP0610K 1M
4.096V
2.2F
CELL1
SD LT1636
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Figure 18. Providing Measurement of Calibration Reference and Full-Stack Voltage Through CELL1 Port
330 3.57k CSBI SDO SDI 3.57k 3.57k
SCKI VREG 100nF 249 LTC6802-1
ACSL-6410 ISOLATED VLOGIC BAT54S 1F BAT54S 6* 4 V- VCC1 1F IN1 470pF 20k
*1
3
33nF
PE68386
Figure 19. Providing an Isolated High-Speed Data Interface
28
+ -
1M 100k TP0610K 330 4.99k OUT1 GND1 VCC2 IN2 OUT2 GND2 LTC1693-2
TP0610K
VDD CH0 CH1 SEL TC4W53FU COM INH VEE VSS
+5V_HOST CSBI 100k SDI 100k SCKI TP0610K 330 TP0610K
SDO
GND_HOST
10k
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LTC6802-1 APPLICATIONS INFORMATION
logic voltage (~4V) to the opto-coupler isolated side, from energy provided by host-furnished 5V. This circuit provides totally galvanic isolation between the batteries and the host processor, with an insulation rating of 560V continuous, 2500V transient. PCB LAYOUT CONSIDERATIONS The VREG and VREF pins should be bypassed with a 1F capacitor for best performance. The LTC6802-1 is capable of operation with as much as 60V between V+ and V-. Care should be taken on the PCB layout to maintain physical separation of traces at different potentials. The pinout of the LTC6802-1 was chosen to facilitate this physical separation. Figure 20 shows the DC voltage on each pin with respect to V- when twelve 3.6V battery cells are connected to the LTC6802-1. There is no more then 5.5V between any two adjacent pins. The package body is used to separate the highest voltage (43.5V) from the lowest voltage (0V).
LTC6802-1 42.5V 42.5V 42.5V 43.2V 43.2V 43.2V 39.6V 39.6V 36V 36V 32.4V 32.4V 28.8V 28.8V 25.2V 25.2V 21.6V 21.6V 18V 18V 14.4V 14.4V CSBO SDOI SCKO V+ C12 S12 C11 S11 C10 S10 C9 S9 C8 S8 C7 S7 C6 S6 C5 S5 C4 S4 CSBI SDO SDI SCKI VMODE GPIO2 GPIO1 WDTB MMB TOS VREG VREF VTEMP2 VTEMP1 NC V- S1 C1 S2 C2 S3 C3
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ADVANTAGES OF DELTA-SIGMA ADCS The LTC6802-1 employs a delta sigma analog to digital converter for voltage measurement. The architecture of delta sigma converters can vary considerably, but the common characteristic is that the input is sampled many times over the course of a conversion and then filtered or averaged to produce the digital output code. In contrast, a SAR converter takes a single snapshot of the input voltage and then performs the conversion on this single sample. For measurements in a noisy environment, a delta sigma converter provides distinct advantages over a SAR converter. While SAR converters can have high sample rates, the fullpower bandwidth of a SAR converter is often greater than 1MHz, which means the converter is sensitive to noise out to this frequency. And many SAR converters have much higher bandwidths - up to 50MHz and beyond. It is possible to filter the input, but if the converter is multiplexed to measure several input channels a separate filter will be required for each channel. A low frequency filter cannot reside between a multiplexer and an ADC and achieve a high scan rate across multiple channels. Another consequence of filtering a SAR ADC is that any noise reduction gained by filtering the input cancels the benefit of having a high sample rate in the first place, since the filter will take many conversion cycles to settle. For a given sample rate, a delta sigma converter can achieve excellent noise rejection while settling completely in a single conversion - something that a filtered SAR converter cannot do. Noise rejection is particularly important in high voltage switching controllers, where switching noise will invariably be present in the measured voltage. Other advantages of delta sigma converters are that they are inherently monotonic, meaning they have no missing codes, and they have excellent DC specifications.
0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 0V TO 5.5V 5.5V 3.1V 1.5V 1.5V 0V 0V 3.6V 3.6V 7.2V 7.2V 10.8V 10.8V
Figure 20. Typical Pin Voltages for 12 3.6V Cells
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LTC6802-1 APPLICATIONS INFORMATION
Converter Details The LTC6802-1's ADC has a second order delta sigma modulator followed by a Sinc2, finite impulse response (FIR) digital filter. The front-end sample rate is 512ksps, which greatly reduces input filtering requirements. A simple 16kHz, 1 pole filter composed of a 100 resistor and a 0.1F capacitor at each input will provide adequate filtering for most applications. These component values will not degrade the DC accuracy of the ADC. Each conversion consists of two phases - an autozero phase and a measurement phase. The ADC is autozeroed at each conversion, greatly improving CMRR. The second half of the conversion is the actual measurement. Noise Rejection Figure 21 shows the frequency response of the ADC. The rolloff follows a Sinc2 response, with the first notch at 4kHz. Also shown is the response of a 1 pole, 850Hz filter (187s time constant) which has the same integrated response to wideband noise as the LTC6802-1's ADC, which is about 1350Hz. This means that if wideband noise is applied to the LTC6802-1 input, the increase in noise seen at the digital output will be the same as an ADC with a wide bandwidth (such as a SAR) preceded by a perfect 1350Hz brickwall lowpass filter. Thus if an analog filter is placed in front of a SAR converter to achieve the same noise rejection as the LTC6802-1 ADC,
10 0 -10 -20 -30 -40 -50 -60 10 100 1k 10k FREQUENCY (Hz) 100k
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Figure 21. Noise Filtering of the LTC6802-1 ADC
the SAR will have a slower response to input signals. For example, a step input applied to the input of the 850Hz filter will take 1.55ms to settle to 12 bits of precision, while the LTC6802-1 ADC settles in a single 1ms conversion cycle. This also means that very high sample rates do not provide any additional information because the analog filter limits the frequency response. While higher order active filters may provide some improvement, their complexity makes them impractical for high-channel count measurements as a single filter would be required for each input. Also note that the Sinc2 response has a 2nd order rolloff envelope, providing an additional benefit over a single pole analog filter.
FILTER GAIN (dB)
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LTC6802-1 PACKAGE DESCRIPTION
G Package 44-Lead Plastic SSOP (5.3mm)
(Reference LTC DWG # 05-08-1754 Rev O)
12.50 - 13.10* (.492 - .516) 1.25 0.12 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23
7.8 - 8.2
5.3 - 5.7 7.40 - 8.20 (.291 - .323)
0.25 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 - 5.60* (.197 - .221)
0.50 BSC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
1.65 - 1.85 (.065 - .073)
2.0 (.079) MAX
PARTING LINE
0 - 8 SEATING PLANE
0.10 - 0.25 (.004 - .010)
0.55 - 0.95** (.022 - .037) 1.25 (.0492) REF
0.50 (.01968) BSC
0.20 - 0.30 (.008 - .012) TYP
0.05 (.002) MIN
G44 SSOP 0607 REV O
NOTE: 1.DRAWING IS NOT A JEDEC OUTLINE 2. CONTROLLING DIMENSION: MILLIMETERS 3. DIMENSIONS ARE IN
MILLIMETERS (INCHES)
4. DRAWING NOT TO SCALE 5. FORMED LEADS SHALL BE PLANAR WITH RESPECT TO ONE ANOTHER WITHIN 0.08mm AT SEATING PLANE
*DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS, BUT DO INCLUDE MOLD MISMATCH AND ARE MEASURED AT THE PARTING LINE. MOLD FLASH SHALL NOT EXCEED .15mm PER SIDE **LENGTH OF LEAD FOR SOLDERRING TO A SUBSTRATE THE MAXIMUM DIMENSION DOES NOT INCLUDE DAMBAR PROTRUSIONS. DAMBAR PROTRUSIONS DO NOT EXCEED 0.13mm PER SIDE
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
31
LTC6802-1 RELATED PARTS
PART NUMBER LTC6802-2 DESCRIPTION Multicell Battery Stack Monitor with Parallel Addressed Serial Interface COMMENTS Functionality equivalent to LTC6802-1, Allows for Individually Addressable Battery Stack Topologies
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32 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0808 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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