ACE7263C

27V 2A 500KHz Synchronous Step-Down DC/DC Converter

VER 1.2

7

Over-current-protection and hiccup

The ACE7263C 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 ACE7263C 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 ACE7263C 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. ACE7263C 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.

Applications Information

Setting output voltages

The external resistor divider is used to set the output voltage. The feedback resistor R1 also sets the

feedback loop bandwidth with the internal compensation capacitor. R2 is then given by:

Selecting the inductor

Use a 2.2μH-to-6.8μH inductor with a DC current

rating of at least 25% higher than the maximum load current for most applications. For most designs,

derive the inductance value from the following equation: