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EV-124
AAT3681: USB Port or AC Adapter
Lithium-Ion/Polymer Battery Charger
Introduction
The AAT3681 evaluation board demonstrates single-cell lithium-ion/polymer battery charging from either a
USB or ADP port. The AAT3681 precisely regulates battery charge voltage and current for 4.2V (4.375V
option) lithium-ion/polymer battery cells. This device operates at an input voltage range from 4V to 6.5V. The
charging current can be set up to 300mA by an external resistor.
This document describes the evaluation board and the value for the set resistor. In addition, a schematic of
the complete evaluation board's circuit (Figure 1) and the board layout (Figures 2 and 3) are provided. For
additional information, please refer to the AAT3681 product datasheet.
Schematic
VBAT
VCC
JP2
Enable
C1
10µF
U1
R8
8.06K
1
2
3
4
EN
ISET
VBAT
VCH
GND
GND
GND
STAT
8
7
6
5
C2
2.2µF
AAT3681
D1
R1
1K
JP1
RED
LED
Figure 1: Evaluation Board Schematic.
Printed Circuit Board
Figure 2: Top Layer (not to scale).
EV-124.2006.03.1.1
Figure 3: Bottom Layer (not to scale).
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EV-124
AAT3681: USB Port or AC Adapter
Lithium-Ion/Polymer Battery Charger
Programming Charge Current
The charging current level is programmed with a resistor placed between the ISET pin and ground. The accuracy of the constant charge current and preconditioning trickle charge current is dominated by the resistor tolerance. A 1% tolerance resistor is recommended.
The constant charge current can be programmed from 15mA to 300mA. Table 1 provides resistor values for
commonly used constant charge current levels. Figure 4 shows the relationship between ICC and RSET.
ICC (mA)
Ω)
Set Resistor Value RSET (kΩ
300
250
200
150
100
50
40
30
20
15
5.36
6.49
8.06
10.7
16.2
31.6
38.3
53.6
78.7
105
Table 1: Recommended RSET Values.
1000
ICC (mA)
100
10
1
1
10
100
1000
RSET (kΩ
Ω)
Figure 4: ICC vs. RSET.
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EV-124
AAT3681: USB Port or AC Adapter
Lithium-Ion/Polymer Battery Charger
LED Status Output
The AAT3681 status pin function provides a visual indication of the status of a battery under charge. The status LED is turned on by an internal MOSFET switch which connects the status pin to ground when the AAT3681
is in the pre-conditioning trickle charge, constant current charge, or constant voltage charge modes. The LED
status indicator is turned off when there is no battery charging or when the charge cycle is complete.
A series resistor (R1) is placed with the status indicator LED (D1) to limit the forward current through the LED.
The nominal value of R1 is 1kΩ; this value may be adjusted by the following formula:
ILED =
VCC - VF
R1
Use of the LED status indicator is optional. To disable this function, remove jumper JP1 which connects the
LED to the input supply.
Enable
The AAT3681 enable pin should be pulled to a logic high level to turn on the device.
EV-124.2006.03.1.1
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EV-124
AAT3681: USB Port or AC Adapter
Lithium-Ion/Polymer Battery Charger
AAT3681 EVAL Component Listing
Component
U1
R1
R8
JP1
C1
C2
JP2
LED1
Part#
Description
AAT3681IJS-T1
USB/ADP Battery Charger;
SC70JW-8 Package
1KΩ, 5%, 1/4W; 0603
8.06KΩ, 1%, 1/4W; 0805
0Ω, 5%, 1/4W; 0603
CER 10µF 10V 10% X5R 0805
CER 2.2µF 10V 10% X7R 0805
Connecting Header, 2mm zip
Red LED; 1206
Chip Resistor
Chip Resistor
Chip Resistor
GRM21BR61A106KE19L
GRM21BR71A225KA01L
PRPN401PAEN
CMD15-21SRC/TR8
Manufacturer
AnalogicTech
Vishay
Vishay
Vishay
Murata
Murata
Sullins Electronics
Chicago Miniature Lamp
Table 3: Component Listing.
© 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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
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EV-124.2006.03.1.1