Secondary Side Housekeeping Circuit

AS23xx

93

ASTEC Semiconductor

Pin Function Description (For AS2333 / AS2350)

Pin Number

Function

Description

Power input to the chip.

2

+12 V

Input for overvoltage and undervoltage for the +12 V rail.

3

+5 V

Input for overvoltage and undervoltage for the +5 V rail.

4

+3.3/–5 V

Input for overvoltage and undervoltage for the +3.3V rail or –5 V rail, depending on

product option.

5

–12 V

Input for overvoltage and undervoltage for the –12 V rail. This function may

disabled by tying this pin to a positive voltage above 2.4 V.

6

GND

Signal ground and silicon substrate.

7

HYST

Open collector output of the AC undervoltage comparator. A resistor between this pin

and AC will provide hysteresis to the AC undervoltage sensing.

8

OFF

Pulling this pin low will reset the FAULT latch and discharge the start-up timing

capacitors, UVB and PG CAP, allowing normal start-up for the system. Pulling this pin

high will send the FAULT signal high, prompting a system shutdown.

9

AC

Non-inverting input to the AC undervoltage sensing comparator. If the AC pin is

less than 2.5 V, POK goes low and UVB cap discharges.

10

PG CAP

A cap to ground provides a delay between undervoltage sensing becoming good

and the POK output going high. Cap discharges whenever an output or AC

undervoltage is detected.

11

POK

Open collector output of the undervoltage sensing comparators. This pin goes low

upon an undervoltage condition. Except for the delay set by the PG CAP, this pin

always reflects the actual state of the undervoltage sensing.

12

DELAY

A cap to ground will delay the FAULT signal when the OFF pin is used to shut down

the system. The POK will signal a power fail warning immediately, but the FAULT

shutdown of the power supply will be delayed.

13

UVB

A cap to ground provides start-up blanking of the undervoltage sensing portion of the

FAULT signal. This pin may also be grounded to prevent undervoltage conditions from

triggering the FAULT signal. This pin discharges the cap whenever AC goes low or

FAULT pin goes high.

14

2.5 V Voltage reference. This is a series regulator type reference.

15

FAULT

Open collector output of the overvoltage and undervoltage comparators.

16

CBD

Crow bar drive output of the overvoltage faults only.