PRODUCT DATASHEET
AAT2688
TM
SystemPower
4.5A PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Pin Descriptions
Pin #
Symbol Function
Channel 1 step-down (Buck) converter switching pin. Connect output inductor to this pin. Connect both
LX1 pins together.
No connect. For optional routing reasons, pins 3 and 4 can be connected to VIN, pin 9 to pin 10 (IN2),
and pin 12 to pin 11 (OUT2).
1, 2, 23, 24
LX1
N/C
3, 4, 9, 12
Channel 1 step-down regulator boost drive input pin. Connect the cathode of fast rectifier from this pin
and connect a 100nF capacitor from this pin to the channel 1 switching node (LX1) for internal hi-side
MOSFET gate drive.
Channel 1 step-down regulator enable input pin. Active high enables internal linear regulator and chan-
nel 1 output.
5
6
BST1
EN1
Ground pin for Channel 2. Power return pin for channel 2. Connect return of channel 2 input and output
capacitors close to this pin for best noise performance.
Channel 2 low dropout (LDO) enable input pin. Active high.
7
8
GND2
EN2
Input supply voltage pin for channel 2 linear low dropout (LDO) regulator. Connect 2.2μF ceramic input
capacitor close to this pin.
10
IN2
Output of channel 2 of linear low dropout (LDO) regulator. Connect a 2.2μF ceramic capacitor from this
pin to GND pin.
Channel 1 output current sense pin. Connect a small signal resistor from this pin to switching node
(LX1) to enable over-current sense for step-down converter. The current limit threshold varies with
sense resistor sizing.
11
13
OUT2
RS1
Channel 1 output sense voltage pin. Connect to the output capacitor to enable over-current sense for
step-down converter.
Compensation pin for channel 1 step-down regulator. Connect a series resistor, capacitor network to
compensate the voltage mode control loop.
Feedback input pin for channel 1 step-down converter. Connect an external resistor divider to this pin to
program the output voltage to the desired value.
14
15
16
OS1
COMP1
FB1
Ground pin for channel 1. Power return pin for channel 1. Connect return of channel 1 input and output
capacitors close to this pin for best noise performance.
Internal linear regulator. Connect a 2.2μF capacitor from this pin to GND pin.
Channel 1 gate drive for low side MOSFET. Connect to the gate pin of an external N type MOSFET (see
the "MOSFET Selection" section of this product datasheet).
17
18, 19
20
GND1
VL1
DL1
Ground pin for both channels. Power return pin for both channels. Connect returns of both channels’
input and output capacitors close to this pin for best noise performance.
21
PGND
Input supply voltage pin for channel 1 step-down regulator. Connect both IN1 pins together. Connect
the input capacitor close to this pin for best noise performance.
Exposed Paddle. Tie to IN1. Connect to PCB heatsink for optimum thermal performance.
22
EP
IN1
EP
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2688.2008.06.1.0
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