APW6021 datasheet(6/13 Pages) ANPEC

6 / 13 page

Rev. P.4 - Mar., 2001

APW6021

www.anpec.com.tw

Functional Pin Description Cont.

VID4, VID3, VID2, VID1, VID0 (Pins 3, 4, 5, 6 and 7)

VID0-4 are the TTL-compatible input pins to the 5-bit

DAC. The logic states of these five pins program the

internal voltage reference (DACOUT). The level of

DACOUT sets the microprocessor core converter

output voltage, as well as the corresponding PGOOD

and OVP thresholds.

PGOOD (Pin 8)

PGOOD is an open collector output used to indicate

the status of the output voltages. This pin is pulled

low when the synchronous regulator output is not

within

±10% of the DACOUT reference voltage or

when any of the other outputs are below their under-

voltage thresholds.

The PGOOD output is open for“11111” VID code.

SD (Pin 9)

This pin shuts down all the outputs. A TTL-

compatible, logic level high signal applied at this

pin immediately discharges the soft-start capacitor,

disabling all the outputs. Dedicated internal circuitry

insures the core output voltage does not go negative

during this process. When re-enabled, the IC under-

goes a new soft-start cycle. Left open, this pin is pulled

low by an internal pull-down resistor, enabling

operation.

VSEN2 (Pin 10)

Connect this pin to the output of the AGP linear

regulator. The voltage at this pin is regulated to the

level predetermined by the logic-level status of the

SELECT pin. This pin is also monitored for under-

voltage events.

SELECT (Pin 11)

This pin determines the output voltage of the AGP

bus linear regulator. A low TTL input sets the output

voltage to 1.5V, while a high input sets the output

voltage to 3.3V.

SS (Pin 12)

Connect a capacitor from this pin to ground. This

capacitor, along with an internal 28

µA current source,

sets the soft-start interval of the converter.

FAULT / RT (Pin 13)

This pin provides oscillator switching frequency

adjustment. By placing a resistor (R

T) from this pin to

GND, the nominal 200kHz switching frequency is in-

creased according to the following equation:

Fs =200kHz + 5

× 10 6 / R

T (kΩ)

T to GND)

Conversely, connecting a resistor from this pin to VCC

reduces the switching frequency according to the fol-

lowing equation:

Fs =200kHz + 4

× 10 7 / R

T (kΩ)

T to 12V)

Nominally, the voltage at this pin is 1.26V. In the event

of an over-voltage or over-current condition, this pin

is internally pulled to VCC.

VSEN4 (Pin 14)

Connect this pin to the output of the linear 1.8V

regulator. This pin is monitored for undervoltage

events.

DRIVE4 (Pin 15)

Connect this pin to the gate of an external MOSFET.

This pin provides the drive for the 1.8V regulator’s

pass transistor.

VAUX (Pin 16)

This pin provides boost current for the linear regula-

tors’ output drives in the event bipolar NPN transis-

tors (instead of N-channel MOSFETs) are employed

as pass elements. The voltage at this pin is moni-

tored for power-on reset (POR) purposes.

GND (Pin 17)

Signal ground for the IC. All voltage levels are mea-

sured with respect to this pin.

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