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Lithium-Ion Linear Battery Charge Controller General Description
The AAT3680 BatteryManagerTM is a member of AnalogicTechTM's Total Power ManagementTM IC (TPM ICTM) product family. This device is an advanced Lithium-Ion (Li-Ion) battery charge and management IC, specifically designed for compact portable applications at lower cost. In a single 8pin package, the AAT3680 precisely regulates battery charge voltage and charge current. This device is capable of two trickle charge current levels controlled by one external pin. Battery charge temperature and charge state are carefully monitored for fault conditions. In the event of an over current, short circuit or over temperature failure, the device will automatically shut down, thus protecting the charging device and the battery under charge. A battery charge state monitor output pin is provided to indicate the battery charge status though a display LED. The battery charge status output is a serial interface which may also be read by a system microcontroller. The AAT3680 is available in an 8-pin MSOP or 12pin TSOPJW package, specified over -20 to 70C range.
AAT3680
Features
* * * * * * * * * * * * * *
BatteryManagerTM
4.5V to 12V Input voltage range 1% Accurate Preset Voltages: 4.1V, 4.2V, 8.2V, 8.4V Low operation current, typically 0.5mA Programmable Charge Current Automatic recharge sequencing Battery temperature monitoring Deep discharge cell conditioning Fast trickle charge option with thermal over-ride Full battery charge auto turn off / sleep mode Over voltage, current and temperature protection Power on reset LED Charge Status Output or System Microcontroller serial interface Temperature range -20 to 70C 8 pin MSOP, 12 pin TSOPJW package
Applications
* * * * Cellular Phones Personal Digital Assistants (PDA's) Desktop Chargers USB Chargers
Typical Application
VP
RSENSE 0.2 Q1 FZT968 SMA
BATT+
C2 1F
B34DLA R1 1.9k DRV T2X VP CSI BAT
BATT-
AAT3680
VP TS
RT1
TEMP
VSS C3 10F RT2 LED1 R2 1k STAT
Battery Pack
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Lithium-Ion Linear Battery Charge Controller Pin Description
Pin #
TSOPJW MSOP
AAT3680
Symbol
CSI BAT VP TS STAT VSS DRV T2X
Function
Current Sense Input. Battery voltage level sense input. Power supply input pin. Battery temperature sense input Battery charge status output. Connect an LED in series with 2.2k from STAT to VP to monitor battery charge state. Common ground connection. Battery charge control output 2 x battery trickle charge control input. Connect this pin to VSS to double the battery trickle charge current. Leave this pin floating for normal trickle charge current (10% of full charge current). To enter microcontroller fast-read status, pull this pin high during power-up. Not connected.
2 1 8, 9, 10, 11 12 7 6 5 4
7 8 1 2 3 4 5 6
3
N/C
Pin Configuration
MSOP-8 (Top View) VP TS STAT VSS
1 8
TSOPJW-12 (Top View) BAT CSI T2X DRV BAT CSI -N/C T2X DRV VSS
1 2 3 4 5 6 12 11 10 9 8 7
2 2
7
3
6
4
5
TS VP VP VP VP STAT
1
2
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Lithium-Ion Linear Battery Charge Controller Absolute Maximum Ratings
Symbol
VP VCSI VT2X VBAT TJ ESD
AAT3680
(TA=25C unless otherwise noted) Value
-0.3 to 16 -0.3 to VP+0.3 -0.3 to 5.5 -0.3 to VP+0.3 -40 to 150 Note 1
Description
VP relative to VSS CSI to GND T2X to GND BAT to GND Operating Junction Temperature Range ESD Rating
Units
V V V V C kV
Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time. Note 1: IC devices are inherently ESD sensitive; handling precautions required.
Thermal Information
Symbol
JA JA PD PD
Description
Maximum Thermal Resistance (TSOPJW-12) Maximum Thermal Resistance (MSOP-8) 2 Maximum Power Dissipation (TSOPJW-12) 2 Maximum Power Dissipation (MSOP-8) 2
2
Value
120 150 1.0 833
Units
C/W C/W W mW
Note 2: Mounted on an FR4 printed circuit board.
Recommended Operating Conditions
Symbol
VP IDRV T
Description
Operation Input Voltage DRV Pin Sink Current Ambient Temperature Range
Conditions
Min
4.5 -20
Typ
Max
12 40 70
Units
V mA C
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Lithium-Ion Linear Battery Charge Controller Electrical Characteristics
values are at TA=25C) Symbol
IP ISLEEP ISTAT(HI) VSTAT(LOW) ISINK VOL@DRV
AAT3680
(VIN = 4.5V to 12V, TA = -20 to 70C unless otherwise noted. Typical Conditions
VIN VIN VIN VIN = = = = 5.5V, VCH = 4.1V, VCH = 4.2V 15V, VCH = 8.2V, VCH = 8.4V 3.5V, VCH = 4.1V, VCH = 4.2V 5.5V
Description
Operating Current Sleep Mode Current STAT high level output leakage current STAT low level sink current DRV pin sink current DRV pin output low
Min
Typ
0.5 0.5 2
Max Units
3 3 6 +1 0.6 1.0 4.125 4.141 4.225 4.242 8.249 8.282 8.450 8.484 110 110 3.06 3.16 6.22 6.32 mA A A V mA V
-1 0.3 20 4.075 4.059 4.175 4.158 8.151 8.118 8.350 8.316 90 90 2.94 3.04 5.98 6.08 0.4 4.100 4.100 4.200 4.200 8.200 8.200 8.400 8.400 100 100 3.0 3.1 6.1 6.2 10 10 1.8 30 60 12 4.00 4.10 8.00 8.20 4.0 4.4 200
VCH
Output Charge Voltage
VCS
Charge Current Regulation
VMIN
Preconditioning Voltage Threshold
VTRICKLE T2X VTS1 VTS2 VTERM VRCH VUVLO VOVP VOCP
Trickle-Charge Current Regulation Trickle Charge Current Gain Low Temperature Threshold High Temperature Threshold Charge termination threshold voltage
VIN = 5.5V, ISINK = 5mA VIN = 5.5V ISINK = 5mA, VIN = 5.5V T = 25C AAT3680-4.1 A see note 1 TA = 25C AAT3680-4.2 see note 1 T = 25C AAT3680-8.2 A see note 1 TA = 25C AAT3680-8.4 see note 1 VIN = 5.5V, VCH = 4.1V, VCH = 4.2V VIN = 12V, VCH = 8.2V, VCH = 8.4V AAT3680-4.1 AAT3680-4.2 AAT3680-8.2 AAT3680-8.4 V = 4.1V, VCH = 4.2V T2X floating CH VCH = 8.2V, VCH = 8.4V T2X = VSS VIN = 15V VIN = 15V
V
mV
V
mV 30.9 61.8 24 4.08 4.182 8.16 8.364 4.5 % VP % VP mV V V V % VCS
VCH = 4.1V VCH = 4.2V Battery Recharge Voltage Threshold VCH = 8.2V VCH = 8.4V Undervoltage Lockout VIN rising, TA = 25C Over-voltage Protection Threshold Over-current Protection Threshold
29.1 58.2 4 3.92 4.018 7.84 8.036 3.5
Note 1: The AAT3680 output charge voltage is specified over 0 to 50C ambient temperature; operation over -20 to 70C is guaranteed by design.
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Lithium-Ion Linear Battery Charge Controller Functional Block Diagram
Microcontroller Read Enable 2x Trickle Charge Control Current Loop Error Amp Loop Select MUX Driver
AAT3680
T2X CSI
DRV
Microcontroller Status Generator
VREF
Voltage Loop Error Amp Charge Status Logic Control MUX
STAT
BAT
Voltage Comparator LED Signal Generator
TS
Temperature Sense Comparator
VSS
VP
Power-On Reset
Under Voltage Lock Out
Over Current / Short Circuit Protection
Functional Description
The AAT3680 is a Linear Charge Controller designed for one and two cell Lithium Ion or Lithium Polymer batteries. It is a full-featured battery management system IC with multiple levels of power savings, system communication and protection integrated inside. Refer to the block diagram and flow chart in this section.
Cell Preconditioning
Before the start of charging, the AAT3680 checks several conditions in order to maintain a safe charging environment. The input supply must be above the minimum operating voltage, or undervoltage lockout threshold (VUVLO), for the charging sequence to begin. Also, the cell temperature, as reported by a thermistor connected to TS pin, must be within the proper window for safe charging. When these conditions have been met, and a battery is connected to the BAT pin, the AAT3680 checks the state of the battery. If the cell voltage is below VMIN, the AAT3680 begins preconditioning the cell. This is performed by charging the cell with 10% of the programmed constant-current amount.
For example if the programmed charge current is 500mA, then the preconditioning mode (trickle charge) current will be 50mA. Cell preconditioning is a safety precaution for deeply discharged cells, and furthermore, limits the power dissipation in the pass transistor when the voltage across the device is largest. The AAT3680 features an optional T2X mode, which allows faster trickle-charging at approximately two times the default rate. This mode is selected by connecting the T2X pin to VSS. If an over-temperature fault is triggered, the fast trickle-charge will be latched off, and the AAT3680 will continue at the default 10% charge current.
Constant Current Charging
The cell preconditioning continues until the voltage on the BAT pin reaches VMIN. At this point, the AAT3680 begins constant-current charging (fast charging). Current level for this mode is programmed using a current sense resistor RSENSE between VP and CSI pins. The CSI pin monitors the voltage across RSENSE to provide feedback for the current control loop. The AAT3680 remains in constant current charge mode until the battery reaches the voltage regulation point, VCH.
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Lithium-Ion Linear Battery Charge Controller
Constant Voltage Charging
When the battery's voltage reaches VCH during constant-current mode, the AAT3680 transitions to constant-voltage mode. The regulation voltage is factory programmed: 4.1V and 4.2V (or 8.2V and 8.4V for two-cell applications) are available to support different anode materials in Lithium Ion cells. In constant-voltage operation, the AAT3680 monitors the cell voltage and terminates the charging cycle when the voltage across RSENSE decreases to approximately 10mV.
AAT3680
Charge Cycle Termination, Recharge Sequence
After the charge cycle is complete, the AAT3680 latches off the pass device and automatically enters power-saving sleep mode. Either of two possible conditions will bring the IC out of sleep mode: the battery voltage at the BAT pin drops below VRCH (recharge threshold voltage) or the AAT3680 is reset by cycling the input supply through the power-on sequence. Falling below VRCH signals the IC that it is time to initiate a new charge cycle.
Power On Reset Power On Reset
UVLO VP > VUVLO
No
Shut Down Shut Down Mode Mode
Yes
Temperature Temperature Fault Fault
No
Temperature Test TS > VTS1 TS < VTS2 Yes Yes Low Current Conditioning Low Current Charge Conditioning (Trickle Charge) Charge
Preconditioning Test VMIN > VBAT
No Yes Current Current Charging Charging Mode Mode
Current Phase Test VCH > VBAT
No Voltage Phase Test
VTERM < I BAT RSENSE
Yes
Voltage Voltage Charging Charging Mode Mode
No < VRCH Charge Complete Charge Complete Latch Off Latch Off
Figure 1: AAT3680 Operational Flow Chart
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Lithium-Ion Linear Battery Charge Controller
Sleep Mode
When the input supply is disconnected, the charger automatically enters power-saving sleep mode. Only consuming an ultra-low 2A in sleep mode, the AAT3680 minimizes battery drain when it is not charging.This feature is particularly useful in applications where the input supply level may fall below the battery charge or under-voltage lockout level. In such cases where the AAT3680 input voltage drops, the device will enter the sleep mode and automatically resume charging once the input supply has recovered from its fault condition. This makes the AAT3680 well suited for USB battery charger applications. it has not yet reached 4.2V to complete the charge cycle. If the battery is removed and then placed back on the charger, the charge cycle will not resume until the battery voltage drops below the VRCH threshold. In another case, a battery under charge is in the constant current mode and the cell voltage is 3.7V when the input supply is inadvertently removed and then restored. The battery is below the VRCH threshold and the charge cycle will immediately resume where it left off.
AAT3680
LED Display
Charge Status Output The AAT3680 provides a battery charge status output via the STAT pin. STAT is an open-drain serial data output capable of displaying five distinct status functions with one LED connected between the STAT pin and VP. There are four periods which determine a status word. Under default conditions each output period is one second long; thus one status word will take four seconds to display through an LED. The five modes include: 1. Sleep/Charge Complete: The IC goes into Sleep mode when no battery is present -OR- When the charge cycle is complete. 2. Fault: When an Over-Current (OC) condition is detected by the current sense and control circuit OR- When an Over-Voltage (OV) condition is detected at the BAT pin -OR- When a battery OverTemperature fault is detected on the TEMP pin. 3. Battery Conditioning: When the charge system is in the 1X or 2X trickle charge mode 4. Constant Current (CC) Mode: When the system is in the constant current charge mode. 5. Constant Voltage (CV) Mode: When the system is in the constant voltage charge mode. An additional feature of the LED status display is for a Battery Not Detected state. When the AAT3680 senses there is no battery connected to the BAT pin, the STAT output will turn the LED on and off at a rate dependant on the size of the output capacitor being used. The LED cycles on for two periods then remains off for two periods. See figure 2 below.
Charge Inhibit
The AAT3680 charging cycle is fully automatic; however, it is possible to stop the device from charging even when all conditions are met for proper charging. Switching the TS pin to either VP or VSS will force the AAT3680 to turn off the pass device and wait for a voltage between the low and high temperature voltage thresholds.
Resuming Charge and the VRCH Threshold
The AAT3680 will automatically resume charging under most conditions when a battery charge cycle is interrupted. Events such as an input supply interruption or under voltage, removal and replacement of the battery under charge or charging a partially drained battery are all possible. The AAT3680 will monitor the battery voltage and automatically resume charging in the appropriate mode based upon the measured battery cell voltage. The feature is useful for systems with an unstable input supply which could be the case when powering a charger from a USB bus supply. This feature is also beneficial for charging or "topping off" partially discharged batteries. The only restriction on resuming charge of a battery is the battery cell voltage must be below the battery recharge voltage threshold (VRCH) specification. There is VRCH threshold hysteresis built into the charge control system. This is done to prevent the charger from erroneously turning on and off one a battery charge cycle is complete. For example, the AAT3680-4.2 has a typical VRCH threshold of 4.1V. A battery under charge is above 4.1V, but is still in the constant voltage mode because
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Lithium-Ion Linear Battery Charge Controller
AAT3680
Charge Status Sleep / Charge Complete Temp., OC, OV Fault Battery Conditioning Constant Current Mode Constant Voltage Mode
Output Status off / off / off / off on / on / off / off on / on / on / on on / on / on / off on / off / off / off
LED Display
on/off
ON OFF ON OFF ON OFF ON OFF ON OFF
on/off
on/off
on/off
Figure 2: LED Display Output
High Speed Data Reporting
An optional system microcontroller interface can be enabled by pulling the T2X pin up to 4.5V to 5.5V during power-up sequence. The T2X pin should be pulled high with the use of a 100k resistor. If the input supply to VP will not exceed 5.5V, then the T2X pin may be tied directly to VP through a 100k resistor. Since this is a TTL level circuit, it may not be pulled higher than 5.5V without risk of damage to the device. When the high speed data report feature is enabled, the STAT output periods are sped up to 40s, making the total status word 160s in length. See Figure 3 below.
An additional feature is the Output Status for Battery Not Detected state. When the AAT3680 senses there is no battery connected to the BAT pin, the STAT pin cycles for two periods, then remains off for two periods. When in High Speed Data Reporting, the AAT3680 will only trickle charge at the 2x trickle charge level. This is because the TX2 pin is pull high the enable the high speed data reporting. A status display LED may not be connected to the STAT pin when the high speed data reporting is being utilized. If both display modes are required, the display LED must be switched out of the circuit before the T2X pin is pulled high. Failing to do so could cause problems with the high speed switching control circuits internal to the AAT3680.
Charge Status Sleep / Charge Complete Temp., OC, OV Fault Battery Conditioning Constant Current Mode Constant Voltage Mode
Output Status HI / HI / HI / HI LO / LO / HI / HI LO / LO / LO / LO LO / LO / LO / HI LO / HI / HI / HI
STAT Level
Figure 3: Microcontroller Interface Logic Output
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Lithium-Ion Linear Battery Charge Controller
RSENSE VP
0.2 Q1 FZT788B
AAT3680
BATT+
VP C2 10F
R1 2.5k DRV CSI VP C1 4.7F R2 100k VSS TX2 BAT TS STAT RT2 100k RT1
BATT-
AAT3680
TEMP
Battery Pack
C3 0.1F
STAT
High Speed Data Reporting Application Schematic
Protection Circuitry
The AAT3680 is truly a highly integrated battery management system IC including several protection features. In addition to battery temperature monitoring, the IC constantly monitors for over-current and over-voltage conditions; if an over-current situation occurs, the AAT3680 latches off the pass device to prevent damage to the battery or the system, and enters shutdown mode until the over-current event is terminated. An over voltage condition is defined as a condition where the voltage on the BAT pin exceeds the maximum battery charge voltage. If an over-voltage condition occurs, the IC turns off the pass device until voltage on the BAT pin drops below the maximum
battery charge constant voltage threshold. The AAT3680 will resume normal operation after the over-current or over voltage condition is removed. During an over-current or over-voltage event, the STAT will report a FAULT signal. In the event of a battery over-temperature condition, the IC will turn off the pass device and report a FAULT signal on the STAT pin. After the system recovers from a temperature fault, the IC will resume operation in the 1X trickle charge mode to prevent damage to the system in the event a defective battery is placed under charge. Once the battery voltage rises above the trickle charge to constant current charge threshold, the IC will resume the constant current mode.
Preconditioning (Trickle Charge) Phase
Constant Current Phase
Constant Voltage Phase
Output Charge Voltage (VCH)
Preconditioning Voltage Threshold (VMIN) Regulation Current (ICHARGE(REG))
Trickle Charge and Termination Threshold
Figure 4: Typical Charge Profile
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Lithium-Ion Linear Battery Charge Controller Applications Information
Choosing an External Pass Device (PNP or PMOS)
The AAT3680 is designed to work with either a PNP transistor or P-Channel Power MOSFET. Selecting one or the other requires looking at the design tradeoffs including performance versus cost issues. Refer to the following design guide for selecting the proper device: PNP Transistor: In this design example, we will use the following conditions: VP=5V (with 10% supply tolerance), ICHARGE(REG) = 600mA, 4.2V single cell Lithium Ion pack. VP is the input voltage to the AAT3680, and ICHARGE(REG) is the desired fast-charge current. 1. The first step is to determine the maximum power dissipation (PD) in the pass transistor. Worst case is when the input voltage is the highest and the battery voltage is at the lowest during fastcharge (this is referred to as VMIN, nominally 3.1V when the AAT3680-4.2 transitions from tricklecharge to constant-current mode). In this equation VCS is the voltage across RSENSE. PD = (VP(MAX) - VCS - VMIN) * ICHARGE(REG) PD = (5.5V - 0.1V - 3.1V) * 600mA PD = 1.38W 2. The next step is to determine which size package is needed to keep the junction temperature below its rated value, TJ(MAX). Using this value, and the maximum ambient temperature inside the system TA(MAX), calculate the thermal resistance RJA required: RJA = RJA (TJ(MAX) - TA(MAX)) PD 3. Choose a collector-emitter (VCE) voltage rating greater than the input voltage. In this example, VP is 5.0V, so a 15V device is acceptable. 4. Choose a transistor with a collector current rating at least 50% greater than the programmed ICHARGE(REG) value. In this example we would select a device with at least 900mA rating. 5. Calculate the required current gain ( or hFE): > 200 MIN = MIN = IC(MAX) IB(MIN) 0.60 0.002
AAT3680
MIN = 300 where IC(MAX) is the collector current (which is the same as ICHARGE(REG)), and IB(MIN) is the minimum amount of base current drive shown in Electrical Characteristics as ISINK. Important Note: The current gain ( or hFE) can vary a factor of 3 over temperature, and drops off significantly with increased collector current. It is critical to select a transistor with , at full current and lowest temperature, greater than the MIN calculated above. In summary, select a PNP transistor with ratings VCE 15V, RJA 80C/W, IC 900mA, MIN 30 in a SOT223 (or better thermal) package. P-Channel Power MOSFET: In this design example, as shown in Figure 5, we will use the following conditions: VP = 5V (with 10% supply tolerance), ICHARGE(REG) = 750mA, 0.4V Schottky diode, 4.2V single cell Lithium Ion pack. VP is the input voltage to the AAT3680, and ICHARGE(REG) is the desired fast-charge current. 1. The first step is to determine the maximum power dissipation (PD) in the pass transistor. Worst case is when the input voltage is the highest and the battery voltage is at the lowest during fastcharge (this is referred to as VMIN, nominally 3.1V when the AAT3680-4.2 transitions from tricklecharge to constant-current mode). In this equation VCS is the voltage across RSENSE, and VD is the voltage across the reverse-current blocking diode. Refer to section below titled Schottky Diode for further details. Omit the value for VD in the equation below if the diode is not used.
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(150 - 40) = 1.38
RJA = 80C/W It is recommended to choose a package with a lower RJA than the number calculated above. A SOT223 package would be an acceptable choice, as it has an R of 62.5C/W when mounted to a PCB with adequately sized copper pad soldered to the heat tab.
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Lithium-Ion Linear Battery Charge Controller
PD = (VP(MAX) - VCS - VD - VMIN) * ICHARGE(REG) PD = (5.5V - 0.1V - 0.4V - 3.1V) * 750mA PD = 1.4W 2. The next step is to determine which size package is needed to keep the junction temperature below its rated value, TJ(MAX). Using this value, and the maximum ambient temperature inside the system TA(MAX), calculate the thermal resistance RJA required: RJA = RJA = (TJ(MAX) - TA(MAX)) PD (150 - 40) 1.4 5. Calculate the required threshold voltage to deliver ICHARGE(REG): VGS = (VCS + VOL@DRV) - VP(MIN) VGS = (0.1V + 0.1V) - 4.5V VGS = -4.3V where VGS is the available gate to source voltage provided by the AAT3680, VCS is the voltage across the sense resistor, VOL@DRV is the rated low voltage at the DRV pin, and VP(MIN) is the worst case input voltage (assuming 10% tolerance on the 5V supply). Choose a MOSFET device with sufficiently low VGS(TH) so the device will conduct the desired ICHARGE(REG). 6. Calculate the worst case maximum allowable RDS(ON) at worst case VGS voltage: RDS(ON) = RDS(ON) = (VP(MIN) - VCS(MAX) - VBAT(MAX)) ICHARGE(REG) (4.5V - 0.11V - 4.242V) 0.75A
AAT3680
RJA = 79C/W It is recommended to choose a package with a lower RJA than the number calculated above. A SOT223 package would be an acceptable choice, as it has an RJA of 62.5C/W when mounted to a PCB with adequately sized copper pad soldered to the heat tab. 3. Choose a drain-source (VDS) voltage rating greater than the input voltage. In this example, VP is 5.0V, so a 12V device is acceptable. 4. Choose a MOSFET with a drain current rating at least 50% greater than the programmed ICHARGE(REG) value. In this example we would select a device with at least 1.125A rating.
Q1 RFD10P03L
RDS(ON) = 197m Select a P-Channel Power MOSFET with RDS(ON) lower than 197m at VGS = -4.3V. In summary, select a P-Channel MOSFET with ratings VDS 12V, RJA 79C/W and RDS(ON) 197m at VGS = -4.3V in a SOT223 (or better thermal) package.
VP
RSENSE 0.2 R4 100k
BATT+
C2 10F
R1 1k DRV T2X VP CSI BAT
BATT-
AAT3680
VP TS
RT1
TEMP
VSS C1 4.7F D1 RT2 STAT
Battery Pack
R2 1k
Figure 5: Typical Applications Schematic Using P-Channel Power MOSFET
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Lithium-Ion Linear Battery Charge Controller
Choosing a Sense Resistor
The charging rate recommended by Lithium Ion cell vendors is normally 1C, with a 2C absolute maximum rating. Charging at the highest recommended rate offers the advantage of shortened charging time without decreasing the battery's lifespan. This means that the suggested fast charge rate for a 500mAH battery pack is 500mA. The current sense resistor, RSENSE, programs the charge current according to the following equation: RSENSE = (VP -VCSI) ICHARGE(REG) be used because the AAT3680 checks to see that the voltage at TS is within a voltage window bounded by VTS1 and VTS2. Please see equations below for specifying resistors: RT1 and RT2 for use with NTC Thermistor RT1 = RT2 5 * RTH * RTC 3 * (RTC - RTH) 5 * RTH * RTC = (2 * RTC) - (7 * RTH)
AAT3680
RT1 and RT2 for use with PTC Thermistor RT1 = RT2 5 * RTH * RTC 3 * (RTC - RTH) 5 * RTH * RTC = (2 * RTH) - (7 * RTC)
Where ICHARGE(REG) is the desired typical charge current during constant-current charge mode. VP-VCSI is the voltage across RSENSE, shown in the Electrical Characteristic table as VCS. To program a nominal 500mA charge current during fast-charge, a 200m value resistor should be selected. Calculate the worst case power dissipated in the sense resistor according to the following equation: P= P= (VCS)2 RSENSE (0.1)2 0.2
Where RTC is the thermistor's cold temperature resistance, and RTH is the thermistor's hot temperature resistance. See thermistor specifications for info. To ensure there is no dependence on the input supply changes, connect divider between VP and VSS. Disabling the temperature-monitoring function is achieved by applying a voltage between VTS1 and VTS2 on the TS pin.
P = 50mW A 500mW LRC type sense resistor from IRC is adequate for this purpose. Higher value sense resistors can be used, decreasing the power dissipated in the sense resistor and pass transistor. The drawback of higher value sense resistors is that the charge cycle time is increased, so tradeoffs should be considered when optimizing the design.
Capacitor Selection
Input Capacitor In general, it is good design practice to place a decoupling capacitor between VP and VSS pins. An input capacitor in the range of 1F to 10F is recommended. If the source supply is unregulated, it may be necessary to increase the capacitance to keep the input voltage above the undervoltage lockout threshold. If the AAT3680 is to be used in a system with an external power supply source, such as a typical AC to DC wall adaptor, then a CIN capacitor in the range of 10F should be used. A larger input capacitor in this application will minimize switching or power bounce effects when the power supply is "hot plugged" in.
Thermistor
The AAT3680 checks battery temperature before starting the charge cycle as well as during all stages of charging. This is accomplished by monitoring the voltage at the TS pin. Either a negativetemperature coefficient thermistor (NTC) or positive-temperature coefficient thermistor (PTC) can
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Lithium-Ion Linear Battery Charge Controller
Output Capacitor The AAT3680 does not need an output capacitor for stability of the device itself. However, a capacitor connected between BAT and VSS will control the output voltage when the AAT3680 is powered up when no battery is connected. The AAT3680 can become unstable if a high impedance load is placed across the BAT pin to VSS. Such a case is possible with aging Li-Ion battery cells. As cells age through repeated charge and discharge cycles, the internal impedance can rise over time. A 10F or larger output capacitor will compensate for the adverse effects of a high impedance load and assure device stability over all operating conditions. voltage phases of the charging cycle, the battery under charge will discharge through the circuit pass transistor rendering it impossible to turn off. If the circuit is unable to turn off, the reverse leakage will eventually discharge the battery. A blocking diode will prevent this undesirable effect. MOSFET Circuit Application An reverse-blocking diode is generally required for the circuit shown in Figure 5. For this application, the blocking diode gives the system protection from a shorted input, when the AAT3680 is used with a P-Channel MOSFET. If there is no other protection in the system, a shorted input could discharge the battery through the body diode of the pass MOSFET. If a reverse-blocking diode is added to the system, a device should be chosen which can withstand the maximum constant- current charge current at the maximum system ambient temperature. Diode Selection Typically, a Schottky diode is used in reverse current blocking applications with the AAT3680. Other lower cost rectifier type diodes may also be used to save cost if sufficient input power supply head room is available. The blocking diode selection should based on merits of the device forward voltage (VF), current rating, input supply level versus the maximum battery charge voltage and cost. First, one must determine what the minimum diode forward voltage drop must be. Refer to the following equation where: VIN(MIN) = Minimum input supply level VBAT(MAX) = Maximum battery charge voltage required VF(TRAN) = Pass transistor forward voltage drop VF(DIODE) = Blocking diode forward voltage VIN(MIN) = VBAT(MAX) + VF(TRAN) + VF(DIODE) Based on the maximum constant current charge level set for the system, the next step is to determine the minimum current rating and power handling capacity for the blocking diode. The constant current charge level itself will dictate what the minimum
AAT3680
Operation Under No-Load
Under no-load conditions, that is when the AAT3680 is powered with no battery connected between the BAT pin and VSS, the output capacitor is charged up very quickly by the trickle charge control circuit to the BAT pin until the output reaches the recharge threshold (VRCH). At this point the AAT3680 will drop into the sleep mode. The output capacitor will discharge slowly by the capacitor's own internal leakage until the voltage seen at the BAT pin drops below the VRCH threshold. This 100mV cycle will continue at approximately 3Hz with a 0.1F capacitor connected. A larger capacitor value will produce a slower voltage cycle. This operation mode can be observed by viewing the STAT LED blinking on and off at the rate established by the COUT value. For Desk Top Charger applications where it might not be desirable to have a "charger ready" blinking LED, a large COUT capacitor in the range of 100F or more would prevent the operation of this mode.
Reverse Current Blocking Diode
Bi-Polar Circuit Application When using the AAT3680 with a PNP transistor, a reverse-blocking diode is not required because there is no current path from BAT to VP. However, it is advisable to still place a blocking diode between the bipolar transistor collector and the BAT pin connection to the circuit output. In the event where the input supply is interrupted or removed during the constant current or constant
3680.2004.08.1.2
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Lithium-Ion Linear Battery Charge Controller
current rating must be for a given blocking diode. The minimum power handling capacity must be calculated based on the constant current amplitude and the diode forward voltage (VF): Where: PD(MIN) = Minimum power rating for a diode selection VF = Diode forward voltage ICC = Constant current charge level for the system PD(MIN) = VF / ICC Schottky Diodes The reason for selecting a Schottky diode for this application is because Schottky diodes have a low forward voltage drop. The forward voltage (VF) for a Schottky diode is typically between 0.3V and 0.4V. A lower VF permits a lower voltage drop at the constant current charge level set by the system, less power will be dissipated in this element of the circuit. Schottky diode allow for lower power dissipation, smaller component package sizes and greater circuit layout densities. Rectifier Diodes Any general purpose rectifier diode can be used with the AAT3680 application circuit in place of a higher cost Schottky type diode. The design tradeoff is a rectifier diode has a high forward voltage drop. VF for a typical silicon rectifier diode is in the range of 0.7V. A higher VF will place a input supply voltage requirement for the battery charger system. This will also require a higher power rated diode since the voltage drop at the constant current charge amplitude will be greater. Refer to the previously stated equations to calculate the minimum VIN and diode PD for a given application.
AAT3680
14
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Lithium-Ion Linear Battery Charge Controller Evaluation Board Schematic
AAT3680
Figure 6: AAT3680 Demo Board Silk Screen / Assembly Drawing
Figure 7: AAT3680 Demo Board Component Side Layout
Figure 8: AAT3680 Demo Board Solder Side Layout
PCB Layout
For the best results, it is recommended to physically place the battery pack as close as possible to the AAT3680's BAT pin. To minimize voltage drops in the PCB, keep the high current carrying traces
adequately wide. For maximum power dissipation in the pass transistor, it is critical to provide enough copper to spread the heat. Refer to AAT3680 demo board PCB layout, see figures 6, 7 and 8 above.
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Lithium-Ion Linear Battery Charge Controller Evaluation Board Bill of Materials
PNP Transistor Example Designator
R3 R2 RT1 RT2 R1 C2 Header/SW1 C1 C3 R4 U1 D1 D2 D3 Q1
AAT3680
Part Type
0.2, 0.5 Watt 1k, 5% 100k, 5% 100k, 5% 3.9k, 5% 1F 2mm, 3 pos 10F 10F Not populated Li Ion Charge Controller IC Green LED 1.0A Schottky Diode 0.0 Ohm jumper PNP Transistor
Footprint
1206 1206 0805 0805 0805 1206
Manufacturer
IRC Various Various Various Various MuRata Sullins MuRata MuRata AnalogicTech Various Diodes Inc. Zetex
Part Number
LRC1206-01-R200F
1206 1206 MSOP-8 1206 SMA SOT223
PRPN031PAEN Select with starting jumper GRM42-6X5R75K10 GRM42-6X5R106K16 AAT3680IKS-4.2 B340LA F2T968
P-Channel Power MOSFET Example Designator
R3 R2 RT1 RT2 R1 C2 Header/SW1 C1 C3 R4 U1 D1 D2 D3 Q1
Part Type
0.2, 0.5W 1k, 5% 100k, 5% 100k, 5% 1k, 5% 1F 2mm, 3 pos 10F 10F 100k, 5% Li Ion Charge Controller IC Green LED 0.0 Ohm jumper 1.0A Schottky Diode 30V P-Ch MOSFET, 0.2
Footprint
1206 1206 0805 0805 0805 1206
Manufacturer
IRC Various Various Various Various MuRata Sullins MuRata MuRata Various AnalogicTech Various Diodes Inc. Various
Part Number
LRC1206-01-R200F
1206 1206 0805 MSOP-8 1206 SMA TO-252
PRPN031PAEN Select with starting jumper GRM42-6X5R75K10 GRM42-6X5R106K16 AAT3680IKS-4.2
B340LA RFD10P03L
16
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Lithium-Ion Linear Battery Charge Controller Ordering Information
Output Voltage MSOP-8 MSOP-8 TSOPJW-12 TSOPJW-12 Package 4.2V 8.4V 4.2V 8.4V Marking ESXYY KPXYY ESXYY Part Number (Tape and Reel) AAT3680IKS-4.2-T1 AAT3680IKS-8.4-T1 AAT3680ITP-4.2-T1 AAT3680ITP-8.4-T1
AAT3680
Note: Sample stock is generally held on all part numbers listed in BOLD. Note 1: XYY = assembly and date code.
Package Information
MSOP-8
4 4 1.95 BSC
3.00 0.10
4.90 0.10
0.60 0.20 PIN 1 0.254 BSC 0.95 REF
3.00 0.10 10 5 0.95 0.15 0.85 0.10
0.075 0.075 0.65 BSC 0.30 0.08
All dimensions in millimeters.
GAUGE PLANE
0.155 0.075
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Lithium-Ion Linear Battery Charge Controller
TSOPJW-12
0.10 0.20 + 0.05 -
AAT3680
2.40 0.10
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
2.85 0.20
7 NOM 3.00 0.10
0.9625 0.0375
0.04 REF
+ 0.10 1.00 - 0.065
0.055 0.045
4 4
0.010
0.15 0.05
0.45 0.15 2.75 0.25
All dimensions in millimeters.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18
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