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APW7045

Advanced PWM and Linear Power Controller

Anpec Electronics 

APW7045

Functional Pin Description (Cont.)

PGOOD (Pin 3)

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 DAC reference voltage or linear regula-

tor output is below under-voltage threshold.

SD (Pin 4)

The pin shuts down all the outputs. A TLL-compatible

, logic level high signal applied at this pin immediately

discharges the soft-start capacitor , disabling all the

outputs . Left open , this pin is pulled low by an inter-

nal pull-down resistor , enabling operation.

(RT to GND, RT ≥ 10kΩ is more accurate)

Conversely, connecting a resistor from this pin to +12V

reduces the switching frequency according to the

following equation :

Fs =200 +

47920

RT

(kHz)

(RT to 12V, RT ≥ 250 kΩ is more accurate)

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.

GND (Pin 8)

FB2 (Pin 5)

Connect this pin to a resistor divider to set the linear

Signal ground for the IC. All voltage levels are

measured with respect to this pin.

regulator output voltage (VMEM). The output voltage

set by the resistor divider is determined using the

following formula :

VMEM=

1.5V

x

(1

+

ROUT

RGND

)

Where ROUT is the resistor connected from VMEM to

COMP and FB1 (Pin 9, and 10)

COMP and FB1 are the available external pins of the

PWM converter error amplifier. The FB1 pin is the

inverting input of the error amplifier. Similarly , the

COMP pin is the error amplifier output. These pins are

used to compensate the voltage-mode control feed-

back loop of the synchronous PWM converter.

FB2, and RGND is the resistor connected from FB2 to

VSEN1 (Pin 11)

ground. The voltage at this pin is also monitored for

Under-Voltage protection.

SS (Pin 6)

Connect a capacitor from this pin to ground. This

capacitor , along with an internal 28uA current source

, sets the soft-start interval of the converter.

This pin is connected to the PWM converter’s output

voltage. The PGOOD and OVP comparator circuits

use this signal to report output voltage status and for

over- voltage protection.

OCSET (Pin 12)

FAULT (Pin 7)

This pin provides oscillator switching frequency

adjustment, referring to the typical performence. By

placing a resistor (RT, kΩ) from this pin to GND, the

nominal 200kHz switching frequency is increased

Connect a resistor (ROCSET ) from this pin to the drain

of PWM converter’s upper MOSFET. ROCSET, an in-

ternal 200µA current source (IOCSET ), and the

MOSFET’s on-resistance(R ) set the converter’s

DS(ON)

over-current (OC) trip point according to the follow-

ing equation:

according to the following equation :

Fs

=200

+

4000

RT

x

(1.16

- 1.4

RT-1

)

(kHz)

IPEAK

=

IOCSET x ROCSET

RDS(ON)

Copyright  ANPEC Electronics Corp.

5

Rev.A.5 - Jan., 2003

www.anpec.com.tw

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