ADP3188 datasheet(13/28 Pages) AD

13 / 28 page

ADP3188

Rev. A | Page 13 of 28

OUTPUT CROWBAR

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 upper

crowbar threshold. This crowbar action stops once the output

voltage falls below the release threshold of approximately 550 mV.

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

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

voltage is due to a short in the high-side MOSFET, this action

current-limits the input supply or blows its fuse, protecting the

microprocessor from being destroyed.

OUTPUT ENABLE AND UVLO

For the ADP3188 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 a logic low, the ADP3188

is disabled. 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 ADP3418 drivers. The ILIMIT being

grounded disables the drivers such that both DRVH and DRVL

are grounded. This feature is important in preventing the dis-

charge of the output capacitors when the controller is shut off.

If the driver outputs were not disabled, a negative voltage could

be generated during output due to the high current discharge of

the output capacitors through the inductors.

ADP3188 Datasheet(PDF) 13 Page - Analog Devices