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19-1465; Rev 2; 12/03
Advanced Lithium-Ion Battery-Pack Protector
General Description
The MAX1666 provides complete protection against overvoltage, undervoltage, overcharge current, overdischarge current, and cell mismatch for 2-cell to 4-cell lithium-ion (Li+) battery packs. The voltage of each cell in the battery pack is checked and compared to the programmable threshold and to the other cells in the pack. The MAX1666 protects the battery pack in an overcurrent condition by disconnecting the pack from the load at a programmable limit. On-chip power MOSFET drivers control external P-channel MOSFETs to disconnect the cells from external terminals when faults occur. The MAX1666 employs a unique timing scheme that allows three modes of operation for optimal performance and battery power conservation. The MAX1666 can operate in a stand-alone configuration or in conjunction with a microcontroller. It is available in four versions: the S version monitors two Li+ cells, the A and V versions monitor three cells, and the X version monitors four cells. When the charge path is disabled by the charge control pin, the MAX1666A reduces current consumption compared to the MAX1666S/V/X.
Features
Overvoltage Protection Programmable Limits from +4.0V to +4.4V Accurate to 0.5% Undervoltage Protection Programmable Limits from +2.0V to +3.0V Accurate to 2.5% Cell Mismatch Protection Programmable Limits from 0 to 500mV Accurate to 10% Overcharge Current Protection Overdischarge Current Protection Low 30A (typ) Operating Supply Current Low 1A (max) Standby Current +28V (max) Input Voltage Available in Small 16-Pin QSOP (MAX1666S) and 20-Pin QSOP (MAX1666A/V/X) Packages
MAX1666A/S/V/X
Applications
2/3/4-Cell Lithium-Ion Battery Pack
PART MAX1666SEEE MAX1666AEEP PART MAX1666S MAX1666A/V MAX1666X NUMBER OF Li+ CELLS 2 3 4 MAX1666VEEP MAX1666XEEP
Ordering Information
TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 20 QSOP 20 QSOP 20 QSOP
Selector Guide
Typical Operating Circuits appear at end of data sheet.
Pin Configurations
TOP VIEW
SRC 1 DSO 2 TKO 3 CGO 4 B2P 5 BIP 6 GND 7 PKN 8 16 VCC 15 REF 14 OVA SRC 1 DSO 2 TKO 3 CGO 4 B3P 5 B3P 6 B2P 7 B1P 8 GND 9 PKN 10 20 UVO 19 VCC 18 REF 17 OVA SRC 1 DSO 2 TKO 3 CGO 4 B4P 5 B3P 6 B2P 7 B1P 8 GND 9 PKN 10 20 UVO 19 VCC 18 REF 17 OVA
MAX1666S
13 UVA 12 MMA 11 PKF 10 CGI 9 DSI
MAX1666A/V
16 UVA 15 MMA 14 WRN 13 PKF 12 CGI 11 DSI
MAX1666X
16 UVA 15 MMA 14 WRN 13 PKF 12 CGI 11 DSI
QSOP
QSOP
QSOP
________________________________________________________________ Maxim Integrated Products
1
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Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
ABSOLUTE MAXIMUM RATINGS
SRC, DSO, TKO, CGO, UVO, PKF, WRN to GND ...-0.3V to +28V VCC, REF, OVA, UVA, MMA to GND ........................-0.3V to +6V B4P to B3P ...............................................................-0.3V to +6V B3P to B2P ...............................................................-0.3V to +6V B2P to B1P ...............................................................-0.3V to +6V B1P to GND ..............................................................-0.3V to +6V PKN to GND...........................................................................2V VCC, CGI, DSI to PKN...............................................-0.3V to +6V Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.3mW/C above +70C)...........667mW 20-Pin QSOP (derate 9.1mW/C above +70C)...........727mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VSRC = 16V, each cell voltage VCELL = 3.6V, 330k load at REF, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Charge-Mode Detection Threshold SYMBOL VSRC - VB_P VSRC - VB_P = 1V, VCGI = VDSI = GND SRC Supply Current MAX1666A only, VSRC - VB3P = 1V, VCGI = 3V, VDSI = GND MAX1666A only, VSRC - VB3P = 1V, VDSI = 3V, VCGI = GND Supply Current Shutdown Supply Current VCC Output Voltage VCC Undervoltage-Lockout Threshold Reference Output Voltage Overvoltage Threshold Overvoltage-Threshold Hysteresis UVA = GND Undervoltage Threshold Undervoltage-Threshold Hysteresis Cell voltage falling VUVA = VREF / 2 UVA = REF 2.925 1.950 VREF Pulse on Cell voltage rising OVA = GND VOVA = VREF / 2 OVA = REF 4.378 3.980 ISUP ISHDN VCC RLOAD 665, 2V < VCELL < 4.4V 3.09 2.7 3.25 2.85 1.221 4.000 4.2 4.400 200 2.000 2.500 3.000 100 3.075 mV 2.050 V 4.422 mV 4.020 V No faults, long-time average current from the top battery terminal B_P CONDITIONS MIN 1 2 2 2 30 10 5 5 45 1 3.41 3.0 A A V V V A TYP MAX UNITS V
2
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Advanced Lithium-Ion Battery-Pack Protector
ELECTRICAL CHARACTERISTICS (continued)
(VSRC = 16V, each cell voltage VCELL = 3.6V, 330k load at REF, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER WRN Early-Warning Threshold WRN Early-Warning-Threshold Hysteresis OVA, UVA, MMA Input Current Cell Mismatch Threshold PKN to GND OverdischargeCurrent Threshold PKN to GND Overcharge-Current Threshold Overcurrent Fault-Timer Delay Overdischarge/OverchargeCurrent Fault-Blanking Time DSO, CGO, UVO Output Sink Current DSO, CGO Output Source Current DSO, CGO, UVO Leakage Current TKO Pulldown Resistance, MAX1666S/V/X TKO Sink Current, MAX1666A Only TKO Leakage Current, MAX1666A Only Minimum B3P Voltage for TKO Low, MAX1666A Only TKO Source Current DSI, CGI Input High Voltage DSI, CGI Input Low Voltage DSI, CGI Input Current WRN Sink Current PKF Sink Current PKF, WRN Leakage Current Undervoltage, Overvoltage, or Mismatch Fault, to DSO, CGO, TKO Transition Delay tF-DELAY V TKO = 16V V TKO = 16V, VCGI = 3V VSRC = VB3P + 1V, ITKO = 0.5mA TKO = GND Referenced to PKN Referenced to PKN VDSI, VCGI = 5V Fault condition, V WRN = 0.4V Fault condition, V PKF = 0.4V V PKF = V WRN = 27V Fault persistent for four consecutive sample periods 180 320 2 4 4 8 0.2 460 1 2 0.45 1 2.4 8 tP-DELAY tI-DELAY No faults, V DSO = V CGO = VUVO = 1V to 27V V DSO = VSRC - 4V and V CGO = VSRC - 4V, fault condition V DSO = V CGO = VUVO = 27V, fault condition 100 1 200 2.5 1 3.6 OVA, UVA, MMA = REF MMA = GND All cells > 2V VMMA = VREF / 2 MMA = REF 450 270 -220 330 1.6 20 2 SYMBOL CONDITIONS Above undervoltage threshold, cell voltage falling MIN TYP 100 200 0.1 0 250 500 300 -200 550 2.4 30 10 0.2 550 330 -180 770 3.2 40 mV mV ms ms A mA A k mA A V mA V V A mA mA A ms mV 20 MAX UNITS mV mV nA
MAX1666A/S/V/X
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Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
ELECTRICAL CHARACTERISTICS
(VSRC = 16V, each cell voltage VCELL = 3.6V, 330k load at REF, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER Charge-Mode Detection Threshold SYMBOL VSRC - VB_P VSRC - VB_P = 1V, VCGI = VDSI = GND SRC Supply Current MAX1666A only, VSRC - VB3P = 1V, VCGI = 3V, VDSI = GND MAX1666A only, VSRC - VB3P = 1V, VDSI = 3V, VCGI = GND Supply Current Shutdown Supply Current VCC Output Voltage VCC Undervoltage-Lockout Threshold Overvoltage Threshold Undervoltage Threshold OVA, UVA, MMA Leakage Cell Mismatch Threshold PKN to GND OverdischargeCurrent Threshold PKN to GND Overcharge-Current Threshold Overcurrent Fault-Timer Delay Overdischarge/OverchargeCurrent Fault-Blanking Time DSO, CGO, UVO Output Sink Current DSO, CGO Output Source Current DSO, CGO, UVO Leakage Current tP-DELAY tI-DELAY No faults; V DSO, V CGO, VUVO = 1V to 27V V DSO = VSRC - 4V and V CGO = VSRC - 4V, fault condition V DSO = V CGO = VUVO = 27V, fault condition OVA = GND OVA = REF UVA = GND UVA = REF OVA, UVA, MMA = REF All cells > 2V, MMA = REF 450 270 -220 330 1.6 20 2 0.2 ISUP ISHDN VCC RLOAD 665, 2V < VCELL < 4.4V 3.09 2.7 3.975 4.373 1.950 2.925 No faults, long-time average current from the top battery terminal B_P CONDITIONS MIN 1 10 5 5 45 1 3.41 3.0 4.025 4.427 2.050 3.075 20 550 330 -180 770 3.2 40 A A V V V V nA mV mV mV ms ms A mA A A TYP MAX UNITS V
4
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Advanced Lithium-Ion Battery-Pack Protector
ELECTRICAL CHARACTERISTICS
(VSRC = 16V, each cell voltage VCELL = 3.6V, 330k load at REF, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER TKO Pulldown Resistance, MAX1666S/V/X TKO Sink Current, MAX1666A Only Minimum B3P Voltage for TKO Low TKO Source Current DSI, CGI Input High Voltage DSI, CGI Input Low Voltage DSI, CGI Input Current WRN Sink Current PKF Sink Current PKF, WRN Leakage Current Undervoltage, Overvoltage, or Mismatch Fault, to DSO, CGO, TKO Transition Delay tF-DELAY V TKO = 16V VSRC = VB3P + 1V, ITKO = 0.5mA TKO = GND Referenced to PKN Referenced to PKN VDSI = VCGI = 5V Fault condition, V WRN = 0.4V Fault condition, V PKF = 0.4V V PKF = V WRN = 27V Fault persistent for four consecutive sample periods 180 2 4 0.2 460 1 2 0.45 1 SYMBOL CONDITIONS MIN 100 1 3.6 TYP MAX UNITS k mA V mA V V A mA mA A ms
MAX1666A/S/V/X
Note 1: Specifications to -40C are guaranteed by design, not production tested.
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Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX1666toc01
SUPPLY CURRENT vs. TEMPERATURE
MAX1666toc02
UNDERVOLTAGE THRESHOLD vs. TEMPERATURE
UVA = REF UNDERVOLTAGE THRESHOLD (V)
MAX1666toc03
770 VCELL = 3.6V 760 SUPPLY CURRENT (nA) 750 740 730 720 710 700 -40 -20 0 20 40 60 80
35 VCELL = 3.6V 33 SUPPLY CURRENT (A)
3.0015
3.0010
31
29
3.0005
27
25 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C)
3.0000 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
OVERVOLTAGE THRESHOLD vs. TEMPERATURE
MAX1666toc04
MISMATCH VOLTAGE THRESHOLD vs. TEMPERATURE
MAX1666toc05
OVERCHARGE THRESHOLD vs. TEMPERATURE
MAX1666toc06
4.400 OVA = REF UNDERVOLTAGE THRESHOLD (V)
501 MISMATCH VOLTAGE THRESHOLD (mV) MMA = REF 500 499 498 497 496 495 -40 -20 0 20 40 60 80
203 OVERCHARGE THRESHOLD (mV)
202
4.395
201
4.390
200
4.385 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
199 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C)
OVERDISCHARGE THRESHOLD vs. TEMPERATURE
MAX1666toc07
OVERDISCHARGE PROTECTION
MAX1666toc08
OVERDISCHARGE RECOVERY TIME
MAX1666toc09
302 OVERDISCHARGE THRESHOLD (mV) 301 300 299 298 297 296 295 -40 -20 0 20 40 60 80
PKN (0.5V/div)
PKN (0.5V/div)
tI-DELAY DSO (10V/div) DSO (10V/div)
tP
100
1ms/div
100ms/div
TEMPERATURE (C)
6
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Advanced Lithium-Ion Battery-Pack Protector
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
OVERCHARGE
MAX1666toc10
MAX1666A/S/V/X
OVERVOLTAGE FAULT
4.5V B1P 123 4 123 4
MAX1666toc11
PKN (0.5V/div)
4.1V REF (1V/div) tP-DELAY CGO (10V/div)
tF-DELAY
tF-DELAY
CGO (10V/div)
100ms/div
100ms/div VCELL2 = VCELL3 = VCELL4 = 4.15V, OVERVOLTAGE THRESHOLD = 4.4V
UNDERVOLTAGE FAULT
MAX1666toc12
CELL MISMATCH FAULT
3.4V 2.9V 1 REF (1V/div) PKF (10V/div) 234 1 2 3 4
MAX1666toc13
3.4V 2.9V 1 23 4 123 4
B1P
REF (1V/div) WRN (10V/div) tF-DELAY tF-DELAY
B1P
tF-DELAY
tF-DELAY
DSO (10V/div)
DSO (10V/div)
100ms/div VCELL2 = VCELL3 = VCELL4 = 3.35V, UNDERVOLTAGE THRESHOLD = 3.0V, UVA = REF
100ms/div VCELL2 = VCELL3 = VCELL4 = 3.6V, CELL MISMATCH THRESHOLD = 0.5V, MMA = REF
UNDERVOLTAGE FAULT WITHOUT CHARGE SOURCE (VSRC < VB4P + 1V)
3.4V 2.9V
MAX1666toc14
DSO (10V/div)
B1P
REF (1V/div) VCC (2V/div)
100ms/div VCELL2 = VCELL3 = VCELL4 = 3.35V, UNDERVOLTAGE THRESHOLD = 3.0V, UVA = REF
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Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
Pin Description
PIN NAME MAX1666X 1 2 MAX1666A/V 1 2 MAX1666S 1 2 SRC DSO Charge Source Input. Provides current for gate drivers DSO, TKO, CGO, and UVO. Discharge Driver Output. Drives external P-channel MOSFET to control discharge. Trickle-Charge Driver Output. Drives external P-channel MOSFET to control trickle-charge current. MAX1666A requires an external pullup resistor of 470k Fast-Charge Driver Output. Drives external P-channel MOSFET to control fast charge. Cell 4 Positive Input. Power supply input for MAX1666X. Cell 3 Positive Input. Power supply input for MAX1666A/V. Cell 2 Positive Input. Power supply input for MAX1666S. Cell 1 Positive Input Ground Battery Pack Negative Terminal. Connect to bottom of current-sense resistor. Ground reference for logic inputs DSI and CGI. Discharge Control Input Charge Control Input Pack Fail Output. PKF goes low when any cell voltage exceeds the mismatch threshold or when a shorted cell is detected. Undervoltage/Overvoltage Warning Output Mismatch Adjust Input. Set the mismatch threshold by a resistordivider from REF to GND. Undervoltage Adjust Input. Set the undervoltage threshold with a resistor-divider from REF to GND. Overvoltage Adjust Input. Set the overvoltage threshold with a resistor-divider from REF to GND. Reference Voltage Output. Minimize PC board stray capacitance on this node. 3.3V Linear Regulator Output. Bypass with a 0.47F min capacitor to GND. Undervoltage Fault Output FUNCTION
3
3
3
TKO
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
4
--
4
-- --
CGO B4P B3P B2P B1P GND PKN DSI CGI PKF WRN MMA UVA OVA REF VCC UVO
5, 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
5 6 7 8 9 10 11
--
12 13 14 15 16
--
8
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Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
CGO SRC SRC DSI
D Q RB CK
"1" Q
D RB CK N
"1"
DSO N
CGI
OV_FAULT CM_FAULT UV_FAULT CQI_FAULT
N
UV_FAULT CM_FAULT DQY_FAULT 30A 30A
N
MAX1666
50kHz OSC B4P B3P B2P BIP GND CELL VOLTAGE SELECTOR CMP_P OSC
GND LATCH_WRN REG EARLY WARNING WARNING GND
LATCH_OV STATE MACHINE LATCH_UV REG OVERVOLTAGE OV-FAULT
OVA UVA MMA REF 1.221V THRESHOLD VOLTAGE SELECTOR CMP_N
CMP
REG UNDERVOLTAGE
UV-FAULT
LATCH_CM
REG CELL MISMATCH
CM-FAULT PKF N
GND 200mV PKN CQI_HI 550ms TIMER SET/RESET DQI_HI 300mV GND SRC CHARGE 1V B4P UV_FAULT BIAS TKO UVO CM_FAULT UV_FAULT CGI OV_FAULT CM_FAULT 30A N SHUTDOWN 3.3V LINEAR REG. VCC DQI_FAULT B4P CQI_FAULT OV_FAULT WARNING UV_FAULT N WRN
GND
Figure 1. Functional Diagram _______________________________________________________________________________________ 9
Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
BATTERY CONNECTED YES SHUTDOWN
VSRC < VB4P + 1V
VSRC > VB4P + 1V
VCC > 2.85V
NO
YES (DISCHARGE CURRENT * RCS) 300mV (>2.4ms) (CHARGE CURRENT * RCS) 200mV (>2.4ms)
CHARGE CURRENT MONITOR
OVERDISCHARGE DSO = H
RESET RESET DS0 = L CGO = L
OVERCHARGE CGO = H
550ms DELAY STANDBY 80ms VCELL < UNDERVOLTAGE THRESHOLD YES CHECK VREF NO LATCH UVF = `1' CELL MISMATCH
SAMPLE 2.5ms
YES NO LATCH MMF = `1'
NO
VREF > 1.1V
YES VCELL < UNDERVOLTAGE WARNING THRESHOLD NO YES LATCH UVW = `1'
VCELL > OVERVOLTAGE THRESHOLD YES NO LATCH OVF = `1'
UVF = `1' AND VSRC < VB4P + 1V NO
YES
GO TO TABLE 2
Figure 2. Cell Fault Monitor 10 ______________________________________________________________________________________
Advanced Lithium-Ion Battery-Pack Protector
REF R1 R3 R5
MAX1666
OVA UVA MMA
R2 GND
R4
R6
parator monitoring VSRC and the top-cell voltage. The MAX1666 remains in shutdown mode as long as VSRC is less than the top-cell voltage. When SRC is connected to an external charger and VSRC is 1V above the top-cell voltage, the device goes into standby mode. The MAX1666 returns to shutdown mode under two conditions: the battery is disconnected and then reconnected, or the device detects an undervoltage fault and no charge source. Normal Mode The standby state activates the bias circuitry, overcurrent comparator, and timer. The standby state lasts 80ms, then the MAX1666 goes into the sample state for 2.5ms. Within the 2.5ms, the MAX1666 checks for overvoltage, undervoltage, and mismatch between cells sequentially, and it stores the results in internal latches. The MAX1666 drives the outputs according to the faults (if any) detected by reading the latches (Figure 2) at the end of the sample state. Then the MAX1666 returns to the standby state.
MAX1666A/S/V/X
Figure 3. Using an External Resistor-Divider to Adjust Overvoltage Threshold
Detailed Description
The MAX1666 battery-pack protectors supervise the charging and discharging processes of Li+ battery cells. Designed for 2-, 3-, and 4-cell applications, these devices monitor the voltage across each cell to provide protection against undervoltage, overvoltage, and overcurrent damage. Control pins CGO, TKO, and DSO allow control of external MOSFET gates. This allows fast charging, trickle charging, and discharging processes (see the Typical Operating Circuits). The voltage of each cell is measured individually. Also, each cell is measured differentially between every other cell of the pack. The MAX1666 contains a state machine, a voltage regulator, an oscillator, and other logic functions to selectively drive CGO, UVO, TKO, DSO, WRN, and PKF (Figure 1).
Overvoltage Protection
The MAX1666 provides overvoltage protection to avoid overcharging of any cell. When any cell is at overvoltage, CGO and TKO go high, turning off the external MOSFETs and stopping the charging process (see the Typical Operating Circuits). WRN goes low. Overvoltage is set when any cell voltage exceeds the overvoltage threshold. Overvoltage threshold is linearly adjustable through an external 1% resistor-divider (Figure 3) from REF. Determine the overvoltage threshold (VOVT) required. VOVT must be between 4V and 4.4V. Set RTOTAL = R1 + R2 = 1M. Calculate R1 and R2 as follows: R2 = [(VOVT - 4V) / (4.4V- 4V)] * RTOTAL R1 = RTOTAL - R2
Modes of Operation
Shutdown Mode The MAX1666 goes into shutdown mode when a battery pack is first connected. The quiescent current is less than 1A. All circuitry is inactive except the com-
Table 1. Operating Modes
MODE STATE Standby Normal Sample Shutdown -- 2.5 -- 250 0.7 All circuitry active. All circuitry inactive. Device enters shutdown when it detects an undervoltage fault and VSRC < VTOP-CELL + 1V (no charge source). 11 TIME (ms) 80 TYPICAL QUIESCENT CURRENT (A) 24 CONDITION Only bias circuitry, overcurrent comparator, and timer are active.
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Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
B4P I4 + V4 + V3 ICB = V4 R B3P I3P I3 B2P I2P + V2 I2 B1P I1P + V1 I1 + V1 + V2 V1 R + V3 V2 R + V4 V3 R ICB = V4 R ICB = V4 R
threshold (VUVT) accuracy including the internal undervoltage-threshold accuracy (2.5%) is 3.2%.
Undervoltage Warning
When any cell drops to 100mV above the undervoltage threshold, WRN goes low. WRN returns high when all cells are 300mV above the undervoltage threshold.
Cell-Mismatch Protection
The MAX1666 disables charging or discharging when mismatch occurs. When any two cells are mismatched, TKO, CGO, UVO, and DSO go high, turning off the external MOSFETs. PKF goes low. PKF has a strong pulldown current (>4mA), and can be used to control an external thermal fuse. The cell-mismatch threshold is linearly adjustable through an external resistor-divider (Figure 3) from REF. Determine the cell-mismatch threshold (VCMT) required. VCMT has to be between 0 and 500mV. Set RTOTAL = R5 + R6 = 1M. Calculate R5 and R6: R6 = (VCMT / 500mV) RTOTAL R5 = RTOTAL - R6 Maximum mismatch of a 1% external resistor-divider is 2%. The total external adjusted cell-mismatch threshold accuracy, including the internal cell-mismatch threshold accuracy (10%), is 12%.
R
R
R
R
V4 R
Figure 4. Cell Voltage Sampling
Maximum mismatch of 1% external resistor-dividers is 2%. The external adjusted overvoltage-threshold accuracy includes the internal overvoltage-threshold accuracy (0.5%) and the error due to the external resistor-divider multiplied by maximum adjustment: 2% 4.4V - 4.0V 4.4V = 0.2%
Cell Voltage Sampling
The MAX1666 does not introduce cell mismatch. When the battery cells are matched, the MAX1666 draws close to zero current from the intermediate cells. Figure 4 shows a simplified diagram of the voltage sampling scheme: B4P: I4 = 3ICB + V4 / R = 4V4 / R = BAT4 current B3P: I3 = I3P + I4 = BAT3 current I3P + ICB = V3 / R I3P = V3 / R - V4 / R I3 = I4 + (V3 - V4) / R = (3V4 + V3) / R B2P: I2 = I2P + I3 = BAT2 current I2P + ICB = V2 / R I2P = V2 / R - V4 / R I2 = I3 + V2 / R - V4 / R = I4 + (V3 - V4) / R + (V2 - V4) / R = (2V4 + V3 + V2) / R B1P: I1 = I1P + I2 = BAT1 current I1P + ICB = V1 / R I1P = V1 / R - V4 / R I1 = I2 + V1 / R - V4 / R = I4 + (V3 - V4) / R + (V2 - V4) / R + (V1 - V4) / R = (V4 + V3 + V2 + V1) / R when V1 = V2 = V3 = V4, I1P = I2P = I3P = 0, and I1 = I2 = I3 = I4 = 4V4 / R
The total external adjusted overvoltage-threshold (VOVT) accuracy is 0.7%.
Undervoltage Protection
The MAX1666 provides undervoltage protection to avoid overdischarging the cells. When any cell is under voltage, UVO, DSO, and CGO go high, turning off the external charging and discharging MOSFETs. TKO remains low to keep the trickle-charge current on. Undervoltage threshold is linearly adjustable through an external resistor-divider (Figure 3) from REF. Determine the undervoltage threshold (VUVT) required. VUVT must be between 2V and 3V. Set RTOTAL = R3 + R4 = 1M. Calculate R3 and R4 as follows: R4 = [(VUVT - 2V) / (3V - 2V)] RTOTAL R3 = RTOTAL - R4 Maximum mismatch of 1% external resistor-dividers is 2.0%, and the error due to the external resistor-divider multiplied by maximum adjustment is 2% (3V - 2V) / 3V = 0.7%. The total external adjusted undervoltage-
12
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Table 2. Truth Table
CONTROL OUTPUTS OCC 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 UVF: Undervoltage fault ODC: Overdischarge current fault 0 H H H 0 H H H L L 0 H H H L 0 H H H L 0 H H H L L L L L L 0 H H H L L 0 H H H L L H H H H H H H 0 H H H L L H 0 H H H L H L 1 PS H H L H L 0 L H H L H L 0 H PS L L H L 0 H L L L H L 0 L PS L L H L 1 PS L L L H L 0 L L L L H L 0 H H H L L H Undervoltage fault early warning Undervoltage fault early warning, overdischarge current fault Undervoltage fault early warning, overcharge current fault Undervoltage fault early warning, disable discharge path Undervoltage fault early warning, disable discharge path, overcharge current fault Undervoltage fault early warning, disable charge path Undervoltage fault early warning, disable charge path, overdischarge current fault Undervoltage fault early warning, disable charge and discharge path Undervoltage fault early warning, mismatch fault Undervoltage fault early warning, mismatch fault, disable discharge path Undervoltage fault early warning, mismatch fault, disable charge path Undervoltage fault early warning, mismatch fault, disable charge and discharge path Undervoltage fault early warning, overvoltage fault, mismatch fault Undervoltage fault early warning, overvoltage fault, mismatch fault, disable discharge path Undervoltage fault early warning, overvoltage fault, mismatch fault, disable charge path Undervoltage fault early warning, overvoltage fault, mismatch fault, disable charge and discharge path OVF: Overvoltage fault CGI: Charge control input MMF: Mismatch fault DSI: Discharge control input 0 H H H L L H 0 H H H L L H 0 H H H L L H 0 H H H L L H 0 H H H L L H 0 H H H L L H Undervoltage fault, mismatch fault, disable charge path Undervoltage fault, mismatch fault, disable charge and discharge path Undervoltage fault, overvoltage fault, mismatch fault Undervoltage fault, overvoltage fault, mismatch fault, disable discharge path Undervoltage fault, overvoltage fault, mismatch fault, disable charge path Undervoltage fault, overvoltage fault, mismatch fault, disable charge and discharge path 0 H H H L L H Undervoltage fault, mismatch fault Undervoltage fault, mismatch fault, disable discharge path 0 H H H L H H Undervoltage fault, disable charge and discharge path 0 H H H L H H Undervoltage fault, disable charge path 0 H H L L H H Undervoltage fault, disable discharge path 0 H H L L H H Undervoltage fault 0 H H H L L H Overvoltage fault, mismatch fault, disable charge and discharge path 0 H H H L L H Overvoltage fault, mismatch fault, disable charge path 0 H H H L L H Overvoltage fault, mismatch fault, disable discharge path 0 H H H L L H Overvoltage fault, mismatch fault 0 H H H L H L Overvoltage fault, disable charge and discharge path 1 PS H H L H L Overvoltage fault, disable charge path, overdischarge current fault 0 L H H L H L Overvoltage fault, disable charge path 0 H H H L H L Overvoltage fault, disable discharge path 1 PS H H L H L Overvoltage fault, overdischarge current fault 0 L H H L H L Overvoltage fault 0 H H H H L H Mismatch fault, disable charge and discharge path 0 H H H H L H Mismatch fault, disable charge path 0 H H H H L H Mismatch fault, disable discharge path 0 H H H H L H Mismatch fault 0 H H H H H L Disable charge and discharge path 1 PS H H H H L Disable charge path, overdischarge current fault 0 L H H H H L Disable charge path 0 H PS L H H L Disable discharge path, overcharge current fault 0 H L L H H L Disable discharge path 0 L PS L H H L Overcharge current fault 1 PS L L H H L Overdischarge current fault 0 L L L H H L Normal operation ODC DSO UVO CGO TKO WRN PKF NOTES DSI 0 0 0 1 1 0 0 1 0 1 0 1 0 0 1 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 0 0 1 1 0 0 1 0 1 0 1 0 1 0 1
CONTROL INPUTS
UVW
UVF
OVF
MMF
CGI
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
1
0
0
0
0
1
0
0
0
0
1
1
0
0
0
1
1
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
1
0
0
1
0
1
0
0
1
0
1
0
0
1
1
0
0
0
1
1
0
0
0
1
1
1
0
0
1
1
1
1
1
0
0
0
1
1
0
0
0
1
1
0
0
1
1
1
0
0
1
1
1
0
1
0
1
1
0
1
0
1
1
0
1
1
1
1
0
1
1
1
1
1
1
0
1
1
1
1
0
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
1
1
0
0
0
1
1
0
0
0
1
1
0
0
1
0
1
0
0
1
0
1
0
0
1
1
1
0
0
1
1
1
0
1
1
0
1
0
1
1
0
1
0
1
1
1
1
0
1
1
1
MAX1666A/S/V/X
______________________________________________________________________________________
PS: Overcurrent fault pulse sampling. (Output goes high for 500ms then resets low to monitor charge/discharge current. Output goes high again if fault persists.)
UVW: Undervoltage fault early warning
OCC: Overcharge current fault
Advanced Lithium-Ion Battery-Pack Protector
13
Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
Overcharge/Overdischarge Current Protection
The MAX1666 checks for overcharge or overdischarge current in standby and sample states. The thresholds are factory preset to 200mV and 300mV, respectively. A charge current makes PKN go below GND. A discharge current makes PKN go above GND. When PKN exceeds the threshold, a fault is acknowledged. CGO goes high when the overcharge threshold is exceeded. DSO goes high when the overdischarge threshold is exceeded. An internal 550ms timer starts. At the end of 550ms, DSO or CGO goes low while the MAX1666 rechecks for an overcharge/overdischarge fault. A persistent fault causes DSO and CGO to return high and restarts the 550ms timer again.
Table 3. MOSFET Selection
P-CHANNEL MOSFETs IRF7404 IRF7406 Si4431 Si4947 (dual) MAXIMUM DRAIN CURRENT (A) 5.3 4.7 4.5 2.5 EA
Truth Table
The MAX1666 has a total of eight signal inputs and six outputs. Table 2 lists all the possible states.
CGO controls the MOSFET for normal charging of the battery. TKO controls the MOSFET for trickle charge of the cells. DSO controls the discharging MOSFET. Use different MOSFETs to optimize each function depending on the maximum charge and discharge rates. Table 3 lists some suitable MOSFETs in a small 8-pin SO package.
Layout Considerations and Bypassing
As with all PC board designs, a careful layout is suggested. Minimize lead lengths to reduce losses in the traces.
Applications Information
Choosing an External MOSFET
The external P-channel MOSFETs act as a gated switch to enable or disable the charging/discharging process.
14
______________________________________________________________________________________
Advanced Lithium-Ion Battery-Pack Protector
Typical Operating Circuits
OVERDISCHARGE PROTECTION P 1 470k 470k 2 DSO P 4 CGO P TRICKLE CHARGE 270 OVERCHARGE PROTECTION 3 5 DSI CGI WRN B4P B3P PKF UVO REF 7 8 B2P 20 18 499k 1% 499k 1% 499k 1% 11 12 14 13 SRC VCC 19 0.47F +3.3V 5mA
MAX1666A/S/V/X
PACK+
TKO
6
B1P
MAX1666X
9
GND
PKN 10
17 OVA 16 UVA 15 MMA 499k 1% 499k 1% 499k 1%
RSENSE 0.05 PACK-
______________________________________________________________________________________
15
Advanced Lithium-Ion Battery-Pack Protector MAX1666A/S/V/X
Typical Operating Circuits (continued)
OVERDISCHARGE PROTECTION P
PACK+
470k
470k 2 DSO P 4 CGO P OVERCHARGE PROTECTION 3 5
1 SRC VCC
19 1F 100k 100k 220k VCC OUT1 OUT2 IN1 IN2 IN3 PACK CONTROLLER 499k 1% 499k 1% 499k 1% GND
+3.3V 5mA
DSI CGI WRN
12 11 14 13
TRICKLE CHARGE 270
TKO
B4P B3P
PKF UVO REF 20 18
6
7 8
B2P
B1P
MAX1666X
9
GND
PKN 10
17 16 UVA 15 MMA OVA 499k 1% 499k 1% 499k 1%
RSENSE 0.05 PACK-
___________________Chip Information
TRANSISTOR COUNT: 4835
16
______________________________________________________________________________________
Advanced Lithium-Ion Battery-Pack Protector
________________________________________________________Package Information
QSOP.EPS
MAX1666A/S/V/X
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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