TOP250 datasheet(24/54 Pages) POWERINT

24 / 54 page

Rev. R 10/20

TOP242-250

www.power.com

Diode D10 for the 5 V output is a PN type to center the

5 V output at 5 V. The 3.3 V and 5 V output require two

capacitors in parallel to meet the ripple current requirement.

Switching noise filtering is provided by L2 to L5 and C8,

C10, C12, C15 and C18. Resistor R6 prevents peak

charging of the lightly loaded 30 V output. The outputs are

regulated using a secondary reference (U3). Both the 3.3

V and 5 V outputs are sensed via R11 and R10. Resistor

R8 provides bias for U3 and R7 sets the overall DC gain.

Resistor R9, C19, R3 and C5 provide loop compensation.

A soft-finish capacitor (C20) eliminates output overshoot.

Processor Controlled Supply Turn On/Off

A low cost momentary contact switch can be used to turn

the TOPSwitch-GX power on and off under microprocessor

control, which may be required in some applications such

as printers. The low power remote OFF feature allows

an elegant implementation of this function with very few

external components, as shown in Figure 45. Whenever

the push button momentary contact switch P1 is closed

by the user, the optocoupler U3 is activated to inform the

microprocessor of this action. Initially, when the power

supply is off (M pin is floating), closing of P1 turns the power

supply on by shorting the M pin of the TOPSwitch-GX to

SOURCE through a diode (remote ON). When the

secondary output voltage V

CC is established, the micro-

processor comes alive and recognizes that the switch P1

is closed through the switch status input that is driven

by the optocoupler U3 output. The microprocessor then

sends a power supply control signal to hold the power

supply in the on-state through the optocoupler U4. If the

user presses the switch P1 again to command a turn off,

the microprocessor detects this through the optocoupler

U3 and initiates a shutdown procedure that is product

specific. For example, in the case of the inkjet printer, the

shutdown procedure may include safely parking the print

heads in the storage position. In the case of products

with a disk drive, the shutdown procedure may include

saving data or settings to the disk. After the shutdown

procedure is complete, when it is safe to turn off the power

supply, the microprocessor releases the M pin by turning

the optocoupler U4 off. If the manual switch and the

optocouplers U3 and U4 are not located close to the M pin,

a capacitor C

M may be needed to prevent noise coupling to

the pin when it is open.

P1 Switch

Status

Power

Supply

ON/OFF

Control

External

Wake-up

Signal

PI-2561-030805

VCC

(+5 V)

RETURN

CONTROL

MICRO-

PROCESSOR/

CONTROLLER

LOGIC

INPUT

LOGIC

OUTPUT

High-Voltage

DC Input

TOPSwitch-GX

1N4148

LTV817A

6.8 k

Ω

1 nF

100 k

Ω

6.8 k

Ω

LTV817A

27 k

Ω

1N4148

µF

Figure 45. Remote ON/OFF using Microcontroller.

TOP250 数据表(PDF) 24 Page - Power Integrations, Inc.

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