FAN3506

6

2. PSON & ON /OFF Delay Block

PSON & On/Off Delay Block is controlled by a Microprocessor.

If a high signal is supplied to the PSON(Pin7), the output of COMP2 becomes high status. The output signal is transferred to

On/Off delay block and PG block.

If no signal is supplied to Pin7, Pin7 maintains high status(=3.2V) for the internal pull-up resistor.

When PSON is high, it produces FPO(Pin5) "High" signal after OFF delay time (about 8ms) for stabilizing system.

Then, all outputs (+3.3V, +5V, +12V) are grounded.

When PSON is changed to "Low", it produces FPO "Low" signal after ON delay time (about 26ms) for stabilizing the

system.

If PSON is low, then FPO is low. That means the main SMPS is Active(operational). When PSON is high, FPO is high and the

main SMPS is turned-off.

On/Off Delay Time can be calculated by following equation. 0.22uF Capacitor is recommended for following equations.

- Ton = (Ctpson*VthH)/Ion=(0.22uF*1.8V)/16uA = 26ms

- Toff = [Ctpson*(V8max-VthL)] / Ioff = [Ctpson*(V8max-VthL)] / (VRd/Rd)

Because Ion current for charging is fixed by internal current source, On delay time is varied by the capacitor value. On the con-

trary, Off Delay time is decided by the Rd value. If the Rd is 27K(Recommended) and the Delay capacitor valuse is 0.22uF,

Toff is 8ms(Typ).

5

FPO

11

8

7

PSON

TPSON

Rd

R1

27K

C1

103

OVP

S

R

Q

Q1

VCC

VCC

VCC

VCC

VCC

VCC

COMP2

COMP3

1.26V

FPO

PSON

PG

lon

1.4V

3.2V

lil

Toff

Ton

loff

1.5V ~ 0.6V

+

_

+

_

_

+