ACE727C

600KHz, 16V, 2A Synchronous Step-Down Converter

VER 1.2

4

DETAILED DESCRIPTION

Internal Regulator

The ACE727C is a current mode step down DC/DC converter that provides excellent transient response

with no extra external compensation components. This device contains an internal, low resistance, high

voltage power MOSFET, and operates at a high 600K operating frequency to ensure a compact, high

efficiency design with excellent AC and DC performance.

Error Amplifier

The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a

current proportional to the difference between the two. This output current is then used to charge or

discharge the internal compensation network to form the COMP voltage, which is used to control the

power MOSFET current. The optimized internal compensation network minimizes the external component

counts and simplifies the control loop design.

Internal Soft-Start

The soft-start is implemented to prevent the converter output voltage from overshooting during startup.

When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.6V.

When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as

the reference. When SS is higher than REF, REF regains control. The SS time is internally fixed to 1ms.

Over-Current-Protection and Hiccup

The ACE727C has cycle-by-cycle over current limit when the inductor current peak value exceeds the

set current limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage

(UV) threshold, typically 30% below the reference. Once a UV is triggered, the ACE727C enters hiccup

mode to periodically restart the part. This protection mode is especially useful when the output is

dead-short to ground. The average short circuit current is greatly reduced to alleviate the thermal issue

and to protect the regulator. The ACE727C exits the hiccup mode once the over current condition is

removed.

Startup and Shutdown

If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block

starts first, generating stable reference voltage and currents, and then the internal regulator is enabled.

The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip:

EN low, VIN low and thermal shutdown. In the shutdown procedure, the signaling path is first blocked to

avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The

floating driver is not subject to this shutdown command.