ACE7255E

24V, 2A, Forced PWM Synchronous Step-Down Converter

VER 1.1

6

Functional Description

The ACE7255E is a synchronous buck regulator ICs that integrates the PWM control, top and bottom

switches on the same die to minimize the switching transition loss and conduction l

The ACE7255E is a wide input range, high efficiency, DC-to-DC step-down switching regulator, capable

of delivering up to 2A of output current, integrated with a 160m

Ω high side and 95mΩ low side MOSFET.

It uses PWM current-mode control scheme. An error amplifier integrates error between the FB signal and

the internal reference voltage. The output of the integrator is then compared to the sum of a

current-sense signal and the slope compensation ramp. This operation generates a PWM signal that

modulates the duty cycle of the power MOSFET to achieve regulation for output voltage.

Forced PWM Operation

A forced PWM DC-DC regulator always switches at a fixed frequency even when the output load is small.

This is to ensure a minimum output voltage ripple over the full load range. It may induce a relatively large

(about 10mA when Vin=12V) input current when load is zero.

Enable

EN is a digital control pin that turns the ACE7255E on and off. Drive EN High to turn on the regulator,

drive it Low to turn it off. An internal 1M

Ω resistor from EN pin to GND allows EN to float to shutdown the

chip. Connecting the EN pin through a pull up resistor or shorted EN to IN will automatically turn on the

chip whenever plug in IN.

Over Current Protection and Hiccup

ACE7255Ehas a cycle-by-cycle over current limit for when the inductor current peak value is over the set

current limit threshold. When the output voltage drop until FB falls below UV threshold (0.2V), the

ACE7255E will enter hiccup mode. It will turn off the chip immediately for 6mS. After that, it will try to

re-starts as normal for 2mS. After 2mS, if FB is still below UV threshold, then the chip enters hiccup mode

again. If FB is higher than UV threshold, it will enter the normal mode.