ACE7333C

28V, 3A, 500KHz Synchronous Step-Down DC/DC Converter

VER 1.2

7

Functional Descriptions

Loop Operation

The ACE7333C is a wide input range, high-efficiency, DC-to- DC step-down switching regulator, capable

of delivering up to 3A of output current, integrated with a

150/90mΩ synchronous MOSFET pair,

eliminating the need for external diode. It uses a 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 MOSFETs to achieve regulation for

output voltage.

Internal Soft-Start

The soft-start is important for many applications because it eliminates power-up initialization problems.

The controlled voltage ramp of the output also reduces peak inrush current during start-up, minimizing

start-up transient events to the input power bus.

Over-Current-Protection and Hiccup

The ACE7333C has a cycle-by-cycle over-current limit for when the inductor current peak value exceeds

the set current-limit threshold. First, when the output voltage drops until FB falls below the Under-Voltage

(UV) threshold (typically 300mV) to trigger a UV event, the ACE7333C enters hiccup mode to periodically

restart. the part. This protection mode is especially useful when the output is dead-shorted to ground. This

greatly reduces the average short-circuit current to alleviate thermal issues and to protect the regulator.

The ACE7333C exits hiccup mode once the overcurrent condition is removed.

Light Load Operation

Traditionally, a fixed constant frequency PWM DC-DC regulator always switches even when the output

load is small. When energy is shuffling back and forth through the power MOSFETs, power is lost due to

the finite RDSONs of the MOSFETs and parasitic capacitances. At light load, this loss is prominent and

efficiency is therefore very low. ACE7333C employs a proprietary control scheme that improves efficiency

in this situation by enabling the device into a power save mode during light load, thereby extending the

range of high efficiency operation.

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.