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Lithium-Ion/Polymer Linear Battery Charger General Description
The AAT3682 is a lithium-ion/polymer linear battery charger. It is designed for compact portable applications with a single-cell battery. The AAT3682 precisely regulates battery charge voltage and charge current, and offers an integrated pass device, minimizing the number of external components required. The AAT3682 charges the battery in three different phases: preconditioning, constant current, and constant voltage. In preconditioning mode, the charge current has two different levels and is controlled by one external pin. Battery charge temperature and charge state are carefully monitored for fault conditions. A battery charge stable monitor output pin is provided to indicate the battery charge status through a display LED or interface to a system controller. The AAT3682 has a sleep mode option for when the input supply is removed. In this mode, it draws only 2.0A of typical current. The AAT3682 is available in a Pb-free, 16-pin QFN44 package and is specified over the -20C to +70C temperature range.
AAT3682
Features
* * * * * * * * * * * * * *
BatteryManagerTM
VIN Range: 4.7V to 6.0V Low Quiescent Current, Typically 0.5mA 1% Accurate Preset Voltage Up to 1A of Charging Current Integrated Pass Device Battery Temperature Monitoring Fast Trickle Charge Option Deep Discharge Cell Conditioning LED Charge Status Output or System Microcontroller Serial Interface Power-On Reset Lower Power Sleep Mode Status Outputs for LED or System Interface Indicates Charge and Fault Conditions Temperature Range: -20C to +70C 16-Pin QFN44 Package
Applications
* * * * * Cellular Telephones Digital Still Cameras Hand-Held PCs MP3 Players Personal Data Assistants (PDAs)
Typical Application
Adapter RSENSE R3
VP Gate
R4
BAT T2X
VP
BATT+ COUT = 1F
DRV CSI VCC
C IN = 10F
BSENSE
R T1
BATT-
TS STAT VSS
LED 1 TEMP
R2 = 1K RT2
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Lithium-Ion/Polymer Linear Battery Charger Pin Description
Pin #
1 2, 3, 8, 12 4
AAT3682
Symbol
TS N/C STAT
Function
Battery temperature sense input. Not connected. Battery charger status output. Connect an LED in series with 2.2k from STAT to VIN for a visual monitor battery charge state or connect to a microcontroller to monitor battery status. A 100k resistor should be placed between STAT and VIN for this function. Common ground connection. Battery charge control output. Battery trickle charge control input. Connect this pin to VSS to double the battery trickle charge current. Leave this pin floating for normal trickle current (10% of full charge current). To enter microcontroller fast-read status, pull this pin high during power up. Battery charge control output. Current regulated output to charge the battery. For best operation, a 0.1F ceramic capacitor should be placed between BAT and GND. Common ground connection. Input voltage for biasing the pass device. Battery charge power input. Current sense input. Battery voltage sense input. AAT3682 bias input power. Exposed paddle (bottom); connect to GND directly beneath the package.
5 6 7
VSS DRV T2X
9 10 11 13 14 15 16 EP
BAT VSS GATE VP CSI BSENSE VCC
Pin Configuration
QFN44-16 (Top View)
BSENSE
15
VCC
16
VP CSI
14 13
TS N/C N/C STAT
1 2 3 4
12 11
N/C GATE VSS BAT
AAT3682
10 9
5
6
7
8
DRV VSS
N/C T2X
2
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Lithium-Ion/Polymer Linear Battery Charger Absolute Maximum Ratings1
Symbol
VIN VCSI VT2X Bias, VBAT TJ
AAT3682
Description
VIN Relative to GND CSI to GND T2X to GND BAT to GND Operating Junction Temperature Range
Value
-0.3 to 6.0 -0.3 to VCC + 0.3 -0.3 to 5.5 -0.3 to VCC + 0.3 -40 to 85
Units
V V V V C
Thermal Information
Symbol
JA PD
Description
Maximum Thermal Resistance2, 3 Power Dissipation (TA = 25C)
Value
50 2.0
Units
C/W W
1. 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. 2. Mounted on an FR4 board. 3. Derate 20mW/C above 25C. 3682.2006.12.1.3
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Lithium-Ion/Polymer Linear Battery Charger Electrical Characteristics1
VIN = 5.0V, TA = -20C to +70C, unless otherwise noted. Typical values are at TA = 25C. Symbol
VIN ICC ISLEEP ISTAT(HI) VSTAT(LOW) VCH VCS ICH VMIN VTRICKLE T2X VTS1 VTS2 VTERM VRCH VUVLO VOVP VOCP
AAT3682
Description
Conditions
5.5V, VCH = 4.2 3.5V, VCH = 4.2 5.5V 5.5V, ISINK = 5mA TA = 25C VBAT = 4.2V See Note 1 VIN = 5.5V, VCH = 4.2 VIN = 5.5V VCH = 4.2V T2X Floating; VCH = 4.2V T2X = VSS = = = =
Min
4.7
Typ
0.5 3.0
Max Units
6.0 3.0 6.0 +1.0 0.6 4.225 4.242 110 1.0 3.16 V mA A A V V mV A V mV
Operation Input Voltage Operating Current VIN Sleep Mode Current VIN STAT High Level Output Leakage Current VIN STAT Low Level Sink Current VIN Output Charge Voltage Regulation Charge Current Regulation Charge Current2 Preconditioning Voltage Threshold Trickle Charge Current Regulation Trickle Charge Current Gain Low Temperature Threshold High Temperature Threshold Charge Termination Threshold Voltage Battery Recharge Voltage Threshold Under-Voltage Lockout Over-Voltage Protection Threshold Over-Current Protection Threshold
-1.0 4.175 4.158 90 3.04 0.3 4.20 4.20 100 3.1 10 1.8 30 60 12 4.1 4.0 4.4 200
VCH = 4.2V VIN Rising, TA = 25C
29.1 58.2 4 4.018 3.5
30.9 %VCC 61.8 %VCC 24 mV 4.182 V 4.5 V V %VCS
1. The AAT3682 output charge voltage is specified over the 0C to 55C ambient temperature range; operation over -20C to 70C is guaranteed by design. 2. 1A of charging current is only for dynamic applications and not DC. In addition, the ambient temperature must be at or below 50C.
4
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Lithium-Ion/Polymer Linear Battery Charger Typical Characteristics
Battery Recharge Threshold Voltage vs.Temperature
(RSENSE = 0.15)
AAT3682
Regulated Output Voltage vs. Charge Current
(RSENSE = 0.15)
Regulated Output Voltage (V)
4.25 4.23 4.21 4.19 4.17 4.15 0 100 200 300 400 500 600 700
Battery Recharge Threshold Voltage (V)
4.20 4.15 4.10 4.05 4.00 3.95 3.90 3.85 3.80 -50 -25 0 25 50 75 100
Temperature (C)
Charging Current (mA)
Regulated Output Voltage vs. Input Voltage
(RSENSE = 0.15)
Regulated Output Voltage vs. Temperature
(RSENSE = 0.15)
Regulated Output Voltage (V)
Regulated Output Voltage (V)
4.40
4.250 4.225 4.200 4.175 4.150 4.125 4.100 -50 -25 0 25 50 75 100
4.30
4.20
4.10
4.00 4.0 4.5 5.0 5.5 6.0 6.5
Input Voltage (V)
Temperature (C)
Trickle Charge Threshold Voltage (V)
Trickle Charge Threshold Voltage vs.Temperature
3.4 3.3 3.2 3.1 3.0 2.9 2.8 -50
Trickle Charge Current vs. Temperature
(RSENSE = 0.15)
Trickle Charge Current (mA)
50 75 100
(RSENSE = 0.15)
170 165 160 155 150 145 140 135 130 -50 -25 0 25 50 75 100
-25
0
25
Temperature (C)
Temperature (C)
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Lithium-Ion/Polymer Linear Battery Charger Typical Characteristics
Charging Current vs. Temperature
(RSENSE = 0.15)
700 700
AAT3682
Charging Current vs. Input Voltage
(RSENSE = 0.15 with External Schottky)
Charging Current (mA)
Charging Current (mA)
690 680 670 660 650 -50
600 500 400 300 200 100 0 4.0
VBAT = 4.1V
VBAT = 3.6V
-25
0
25
50
75
100
4.5
5.0
5.5
6.0
Temperature (C)
Input Voltage (V)
Charging Current vs. Battery Voltage
(RSENSE = 0.15 with External Schottky)
Trickle Charge Current vs. Input Voltage
(RSENSE = 0.15; 1.8X Mode)
Trickle Charge Current (mA)
5.0
700
170 165 160 155 150 145 140 135 130 4.0 4.5 5.0 5.5 6.0
Charging Current (mA)
600 500 400 300 200 100 0 2.5
VIN = 4.5V
VIN = 5.5V VIN = 4.75V
3.0
3.5
4.0
4.5
Battery Voltage (V)
Input Voltage (V)
Charging Current vs. Input Voltage
(RSENSE = 0.2 with External Schottky)
Trickle Charge Current vs. Input Voltage
(RSENSE = 0.2; 1.8X Mode)
500 400 300 200 100 0 4.0
Trickle Charge Current (mA)
600
104 102 100 98 96 94 4 4.5 5 5.5 6
Charging Current (mA)
VBAT = 4.0V
VBAT = 3.6V
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
6
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Lithium-Ion/Polymer Linear Battery Charger Typical Characteristics
Charging Current vs. Battery Voltage
(RSENSE = 0.2 with External Schottky)
AAT3682
Safe Operating Area
(TJ(MAX) = 120C)
Maximum Input Voltage (V)
600
7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0.0 0.2 0.4 0.6 0.8 Schottky VF = 0.2V TAMB = 85C TAMB = 70C TAMB = 50C TAMB = 40C
Charging Current (mA)
500 400 300 200 100 0 2.5
VIN = 4.5V VIN = 5.5V VIN = 4.75V
3.0
3.5
4.0
4.5
5.0
Battery Voltage (V)
Charging Current (A)
Safe Operating Area
(TJ(MAX) = 150C)
Maximum Input Voltage (V)
6.2 6.0 5.8 5.6 5.4 5.2
Schottky VF = 0.2V TAMB = 85C TAMB = 70C TAMB = <50C
5.0 0 0.2 0.4 0.6 0.8
Charging Current (A)
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Lithium-Ion/Polymer Linear Battery Charger Functional Block Diagram
AAT3682
VP
BAT GATE
T2X
2X Trickle Charge Control
Loop Select MUX Driver
DRV
CSI
Current Loop Error Amp
Microcontroller Status Generator
STAT
VREF
Voltage Loop Error Amp
Charge Status Logic Control
MUX
BSENSE
LED Signal Generator
Voltage Comparator
Microcontroller Read Enable
T2X
VSS
TS
Temperature Sense Comparator
VCC
Power-On Reset
Under-Voltage Lock Out
Over-Current / Short-Circuit Protection
Functional Description
The AAT3682 is a linear charger designed for singlecell lithium-ion/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 above and the flow chart and typical charge profile graph (Figures 1 and 2) in this section.
Cell Preconditioning
Before the start of charging, the AAT3682 checks several conditions in order to maintain a safe charging environment. The input supply must be above the minimum operating voltage, or under-voltage lockout threshold (VUVLO), for the charging sequence to begin. Also, the cell temperature, as reported by a thermistor connected to the TS pin, must be within the proper window for safe charging.
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Lithium-Ion/Polymer Linear Battery Charger
AAT3682
Power On Reset Power On Reset
UVLO VCC > 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 Current Current Charging Charging Mode Mode
Current Phase Test VCH > VBAT
Yes
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: AAT3682 Operational Flow Chart.
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 2: Typical Charge Profile.
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Lithium-Ion/Polymer Linear Battery Charger
When these conditions have been met and a battery is connected to the BAT pin, the AAT3682 checks the state of the battery. If the cell voltage is below VMIN, the AAT3682 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 power dissipation in the pass transistor when the voltage across the device is largest. The AAT3682 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 AAT3682 will continue at the default 10% charge current. (recharge threshold voltage) or the AAT3682 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.
AAT3682
Sleep Mode
When the input supply is disconnected, the device automatically enters power-saving sleep mode. Only consuming an ultra-low 2A current, the AAT3682 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 AAT3682 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 AAT3682 well suited for USB battery charger applications.
Constant Current Charging
The cell preconditioning continues until the voltage on the BAT pin reaches VMIN. At this point, the AAT3682 begins constant current charging (fast charging). Current level for this mode is programmed using a current sense resistor RSENSE between the VCC and CSI pins. The CSI pin monitors the voltage across RSENSE to provide feedback for the current control loop. The AAT3682 remains in constant current charge mode until the battery reaches the voltage regulation point, VCH.
Charge Inhibit
The AAT3682 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 VIN or GND will force the AAT3682 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 AAT3682 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 AAT3682 will monitor the battery voltage and automatically resume charging in the appropriate mode based upon the measured battery cell voltage. This feature is useful for systems with an unstable input supply, which could be the case when powering a charger from a USB bus supply. It is also beneficial for charging or "topping off" partially discharged batteries. The only restriction on resuming charge of a battery is that the battery cell voltage must be below the battery recharge voltage threshold (VRCH) specification. There is VRCH threshold hysteresis built into the charge control
Constant Voltage Charging
When the battery voltage reaches VCH during constant current mode, the AAT3682 transitions to constant voltage mode. The regulation voltage is factory programmed to 4.2V. In constant voltage operation, the AAT3682 monitors the cell voltage and terminates the charging cycle when the voltage across RSENSE decreases to approximately 10mV.
Charge Cycle Termination, Recharge Sequence
After the charge cycle is complete, the AAT3682 shuts 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 10
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Lithium-Ion/Polymer Linear Battery Charger
system. This is done to prevent the charger from erroneously turning on and off once a battery charge cycle is complete. For example, the AAT3682 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 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. 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 -ORwhen 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 over-temperature fault is detected on the TEMP pin. 3. Battery Conditioning: When the charge system is in 1X or 2X trickle charge mode. 4. Constant Current (CC) Mode: When the system is in constant current charge mode. 5. Constant Voltage (CV) Mode: When the system is in constant voltage charge mode. An additional feature of the LED status display is for a Battery Not Detected state. When the AAT3682 senses there is no battery connected to the BAT pin, the STAT output will turn the LED on and off at a rate dependent on the size of the output capacitor being used. The LED cycles on for two periods then remains off for two periods. See Figure 3 below.
AAT3682
LED Display Charge Status Output
The AAT3682 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,
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 3: LED Display Output.
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Lithium-Ion/Polymer Linear Battery Charger
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 the power-up sequence. The T2X pin should be pulled high with the use of a 100k resistor. If the input supply to VIN will not exceed 5.5V, then the T2X pin may be tied directly to VIN 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 4 below. An additional feature is the Output Status for the Battery Not Detected state. When the AAT3682 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 AAT3682 will only trickle charge at the 2X trickle charge level. This is because the T2X pin is pulled high to 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 AAT3682.
AAT3682
Charge Complete LED Status Mode
A simplified LED status can be obtained by configuring the AAT3682 for high-speed data reporting mode (T2X tied to VCC) and installing a 0.047F capacitor from the STAT pin to the VSS pin (see Figure 5). In this configuration, the LED will be illuminated for all modes except the Sleep/Charge Complete mode. In addition, the T2X input must be tied to VCC through a 100k resistor. In this mode, the trickle charge current will be 1.8X the normal trickle charge level. To reset the trickle charge current to the 1X level, the TS input must be temporarily toggled low. Removing C3 forces the LED status to gradually dim as the battery becomes fully charged (see Figure 5).
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 4: Microcontroller Interface Logic Output.
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Lithium-Ion/Polymer Linear Battery Charger
VIN
2 1
AAT3682
R2 C1 22F 0.2 R1 2.2K R5 100K
J1 GND
C5 4.7F
1 2 3 4
D2 Green LED R6 100K
TS N/C N/C STAT
13 14 15 16
U1 AAT3682
12 11 10 9
R3 1K
C4 1000pF J2 D1 C2 10F
1 2 3
VP CSI BSENSE VCC
N/C GATE VSS BAT
N/C T2X DRV VSS
Remove capacitor for progressive dimming
C3 47nF
R4 1K
8 7 6 5
R7 100K
3 1
S1
2
SW-T2X
Figure 5: Evaluation Board Schematic.
Protection Circuitry
The AAT3682 is 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 overvoltage conditions; if an over-current situation occurs, the AAT3682 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 AAT3682 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.
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Applications Information
Choosing a Sense Resistor
The charging rate recommended by lithiumion/polymer 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. Refer to the Safe Operating Area curves in the Typical Characteristics section of this datasheet to determine the maximum allowable charge current for a given input voltage. The current sense resistor, RSENSE, programs the charge current according to the following equation:
RSENSE =
VCC - VCSI ICHARGE
Where ICHARGE is the desired typical charge current during constant current charge mode. VCC - VCSI is the voltage across RSENSE, shown in the Electrical Characteristics table as VCS. To program a nominal 500mA charge current during fast charge, a 200m value resistor should be selected. 13
Lithium-Ion/Polymer Linear Battery Charger
Calculate the worst case power dissipated in the sense resistor according to the following equation: perature-monitoring function is achieved by applying a voltage between VTS1 and VTS2 on the TS pin.
AAT3682
P=
VCS2 0.1V2 = = 50mW 0.2 RSENSE
Capacitor Selection
Input Capacitor
In general, it is good design practice to place a decoupling capacitor between the VCC 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 AAT3682 is to be used in a system with an external power supply source, such as a typical AC-to-DC wall adapter, 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.
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.
Thermistor
The AAT3682 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 negative temperature coefficient thermistor (NTC) or positive-temperature coefficient thermistor (PTC) can be used because the AAT3682 checks to see that the voltage at TS is within a voltage window bounded by VTS1 and VTS2. Please see the following equations for specifying resistors: RT1 and RT2 for use with NTC Thermistor:
5 * RTH * RTC RT1 = 3 * (R - R ) TC TH 5 * RTH * RTC RT2 = (2 * R ) - (7 * R ) TC TH
Output Capacitor
The AAT3682 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 AAT3682 is powered up when no battery is connected. The AAT3682 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/poly 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.
RT1 and RT2 for use with PTC Thermistor:
5 * RTH * RTC RT1 = 3 * (R - R ) TH TC 5 * RTH * RTC RT2 = (2 * R ) - (7 * R ) TH TC
Power Dissipation
The voltage drop across the VP and BAT pins multiplied times the charge current is used to determine the internal power dissipation. The maximum power dissipation occurs when the input voltage is at a maximum and the battery voltage is at the minimum preconditioning voltage threshold. This power is then multiplied times the package theta to determine the maximum junction temperature. The worst case power junction temperature is calculated as follows:
Where RTC is the thermistor's cold temperature resistance and RTH is the thermistor's hot temperature resistance. See thermistor specifications for additional information. To ensure there is no dependence on the input supply changes, connect divider between VCC and VSS. Disabling the tem-
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Lithium-Ion/Polymer Linear Battery Charger
PMAX = (VIN(MAX) - VSENSE - VSCHOTTKY - VBAT(MIN)) ICHG(MAX) = (5.5V - 0.1V - 0.2V - 3.04V) 550mA = 1.2W
This equation can be used to determine the maximum input voltage given the maximum junction and ambient temperature and desired charge current. Charge Status
No Battery Connected Battery Condition Constant Current Constant Voltage Sleep/Charge Complete
AAT3682
LED Display
Blinking 100% LED Light 75% LED Light 25% LED Light Off
Table 1: Charging Status. For applications where gradual dimming of the LED is not desired, adding C3 (refer to Figure 5) between the STAT pin and VSS will alter the charging status. In addition, the AAT3682 must be configured to operate in the high frequency STAT mode by connecting the T2X pin to VCC via 100k resistor. As the battery is transitioning from trickle charge to constant current charge and constant voltage, the LED will remain illuminated. Once the battery is fully charged, the LED will shut off, indicating completion of charge. Table 2 summarizes the conditions. Charge Status
No Battery Connected Battery Condition Constant Current Constant Voltage Sleep/Charge Complete
VIN(MAX) = =
TJ(MAX) - TAMB + VBAT + VSCHOTTKY + VCS ICHG(MAX) 120C - 70C + 3.1V + 0.2V + 0.1V 50C/W 500mA
= 5.3V
Operation Under No-Load
Under no-load conditions (i.e., when the AAT3682 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 AAT3682 will drop into 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 desktop 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. The AAT3682 features a charge status output. Connecting a LED to the STAT pin will display all the three conditions of battery operation. Once the adapter is connected to the battery charger, the LED will be fully illuminated. As the battery charges, the LED will gradually dim as it transitions to constant current mode and to constant voltage mode. Table 1 summarizes the conditions.
LED Display
Blinking On On On Off
Table 2: Charging Status With C3 Connected.
Reverse Current Blocking Diode
A reverse blocking diode is generally required for the circuit shown in Figure 5. The blocking diode gives the system protection from a shorted input. If there is no other protection in the system, a shorted input could discharge the battery through the body diode of the internal pass MOSFET. If a reverse blocking diode is added to the system, a device should be chosen that can withstand the maximum constant current charge current at the maximum system ambient temperature. Additionally, the blocking diode will prevent the battery from being discharged to the UVLO level by the AAT3682 in the event that power is removed from the input to the AAT3682. For this reason, the blocking diode must be placed in the location shown in Figure 5.
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Lithium-Ion/Polymer Linear Battery Charger
Diode Selection
Typically, a Schottky diode is used in reverse current blocking applications with the AAT3682. Other lower cost rectifier type diodes may also be used if sufficient input power supply headroom 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 the appropriate minimum diode forward voltage drop: VIN(MIN) = VBAT(MAX) + VF(TRAN) + VF(DIODE) 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 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 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
AAT3682
Schottky Diodes
Schottky diodes are selected for this application because they have a low forward voltage drop, 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. A Schottky diode allows 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 AAT3682 application circuit in place of a higher cost Schottky diode. The design trade-off is that 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 an 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.
PD(MIN) =
VF ICC
16
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Lithium-Ion/Polymer Linear Battery Charger
AAT3682
Figure 6: Evaluation Board Top Side Layout.
Figure 7: Evaluation Board Bottom Side Layout.
Reference
Component Designator Description
U1 C1 C2 C3 R1 R2 R3 R4 R5 R6 R7 J1 J2 S1 D1 D2
Footprint
Part Number
AAT3682-4.2 GRM32ER61A226KA65L GRM21BR61A106KE19L VJ0805Y473KXQA CRCW04022211F RL1220S-R20-F CRCW04021003F CRCW04021001F CRCW04021003F CRCW04021003F CRCW04021003F 277-1273-ND 277-1274-ND S2105-40-ND L62215CT-ND B340LADITR-ND
Manufacturer
AnalogicTech muRata muRata Vishay Vishay SSM Susumu Vishay Vishay Vishay Vishay Vishay
Battery Charger AAT3682 QFN44-16 Ceramic Capacitor 20F-10V-X5R 1210 Ceramic Capacitor 10F-10V-X5R 0805 Ceramic Capacitor 0.047F-10V-X7R 0805 Resistor 2.2k 1/4W 0402 Current Sensing Resistor 0.2 1/4W 0805 Resistor 1.0k 1% 1/4W 0402 Resistor 1.0k 1% 1/4W 0402 Resistor 100k 1% 1/4W 0402 Resistor 100k 1% 1/4W 0402 Resistor 100k 1% 1/4W 0402 4-Pin Socket Connector 4 Pin 6-Pin Socket Connector 6 Pin Jumper Stand Switch 2mm Jumper Green LED 1206 3.0A Schottky Diode SMA
Chicago Miniature Diodes Incorporated
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Lithium-Ion/Polymer Linear Battery Charger Ordering Information
Output Voltage
4.2V
AAT3682
Package
QFN44-16
Marking1
MGXXY
Part Number (Tape and Reel)2
AAT3682ISN-4.2-T1
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
Package Information3
0.600 0.050
Pin 1 Dot By Marking
0.330 0.050
13 16
Pin 1 Identification
0.650 BSC
1
4.000 0.050
R0.030Max
9 4
8
5
4.000 0.050
2.280 REF
Top View
Bottom View
2.400 0.050
0.0125 0.0125
0.203 0.025
Side View
All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
(c) Advanced Analogic Technologies, Inc. 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. Customers are advised 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. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737- 4600 Fax (408) 737- 4611 18
3682.2006.12.1.3
0.900 0.050
0.450 0.050

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