NX2124/2124A

4

Rev.1.8

02/28/08

PIN DESCRIPTIONS

PIN #

PIN SYMBOL

PIN DESCRIPTION

This pin supplies voltage to the high side driver. A high frequency

ceramic capacitor of 0.1 to 1 uF must be connected from this pin to SW pin.

High side MOSFET gate driver.

Ground pin.

Low side MOSFET gate driver. For the high current application, a 4.7nF capaci-

tor is recommended to be placed on low side MOSFET's gate to ground. This is

to prevent undesired Cdv/dt induced low side MOSFET's turn on to happen,

which is caused by fast voltage change on the drain of low side MOSFET in

synchronous buck converter and lower the system efficiency.

Voltage supply for the internal circuit as well as the low side MOSFET gate

driver. A 1uF high frequency ceramic capacitor must be connected from this pin

to GND pin.

This pin is the error amplifier inverting input. This pin is also connected to the

output UVLO comparator. When this pin falls below 0.56V, both HDRV and

LDRV outputs are in hiccup.

This pin is the output of the error amplifier and together with FB pin is used to

compensate the voltage control feedback loop. This pin is also used as a shut

down pin. When this pin is pulled below 0.3V, both drivers are turned off and

internal soft start is reset.

This pin is connected to the source of the high side MOSFET and provides

return path for the high side driver. Also SW senses the low side MOSFETS

current, when the pin voltage is lower than 360mV for NX2124, 540mV for NX2124A,

hiccup will be triggered.

1

BST

2

HDRV

3

GND

4

LDRV

5

Vcc

6

FB

7

COMP

8

SW