FAN5182(2005) View Datasheet(PDF) - Fairchild Semiconductor

Part Name

Description

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FAN5182
(Rev.:2005)

Adjustable Output, 1-, 2-, or 3-Phase Synchronous Buck Controller

Fairchild Semiconductor 

Power Good Monitoring

The power good comparator monitors the output voltage via the

FB pin. The PWRGD pin is an open-drain output whose high

level (when connected to a pull-up resistor) indicates that the

output voltage is within the nominal limits specified in the electri-

cal characteristic table. PWRGD goes low if the output voltage

is outside of this specified range or whenever the EN pin is

pulled low. Figure 8. shows the PWRGD response when the

input power supply is switched off.

Figure 8. Shutdown Waveforms

As part of the protection for the load and output components of

the supply, the PWM outputs are driven low (turning on the low-

side MOSFETs) when the output voltage exceeds the crowbar

trip point. This crowbar action stops once the output voltage falls

below the reset threshold of approximately 650mV.

Turning on the low-side MOSFETs pulls down the output as the

reverse current builds up in the inductors. If the output over volt-

age is due to a short in the high-side MOSFET, this crowbar

action can trip the input supply over current protection or blow

the input fuse, protecting the load from being damaged.

Enable and UVLO

For the FAN5182 to begin switching, the input supply (VCC) to

the controller must be higher than the UVLO threshold, and the

EN pin must be higher than its logic threshold. If UVLO is less

than the threshold or the EN pin is logic low, the FAN5182 is dis-

abled. This holds the PWM outputs at ground, shorts the

DELAY capacitor to ground, and holds the ILIMIT pin at ground.

In the application circuit, the ILIMIT pin should be connected to

the OD pins of the FAN5009 drivers. Grounding the ILIMIT pin

will disable the drivers such that both HDRV and LDRV are hold-

ing low. This feature is important in preventing fast discharge of

the output capacitors when the controller shuts off. If the driver

outputs are not being disabled, a negative output voltage can be

generated due to high current being discharged from the output

capacitors through the inductors.

11

FAN5182 Rev. 1.0.1

www.fairchildsemi.com

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