MC3425 Ver la hoja de datos (PDF) - ON Semiconductor

Número de pieza

componentes Descripción

Lista de partido

MC3425

Power Supply Supervisory/Over and Undervoltage Protection Circuit

ON Semiconductor 

MC3425

CIRCUIT DESCRIPTION

The MC3425 is a power supply supervisory circuit

containing all the necessary functions required to monitor

over and undervoltage fault conditions. The block diagram

is shown below in Figure 15. The Overvoltage (O.V.) and

Undervoltage (U.V.) Input Comparators are both referenced

to an internal 2.5 V regulator. The U.V. Input Comparator

has a feedback activated 12.5 μA current sink (IH) which is

used for programming the input hysteresis voltage (VH).

The source resistance feeding this input (RH) determines the

amount of hysteresis voltage by VH = IHRH = 12.5 × 10−6

RH.

Separate Delay pins (O.V. DLY, U.V. DLY.) are provided

for each channel to independently delay the Drive and

Indicator outputs, thus providing greater input noise

immunity. The two Delay pins are essentially the outputs of

the respective input comparators, and provide a constant

current source, IDLY(source), of typically 200 μA when the

noninverting input voltage is greater than the inverting input

level. A capacitor connected from these Delay pins to

ground, will establish a predictable delay time (tDLY) for the

Drive and Indicator outputs. The Delay pins are internally

connected to the noninverting inputs of the O.V. and U.V.

Output Comparators, which are referenced to the internal

2.5 V regulator. Therefore, delay time (tDLY) is based on the

constant current source, IDLY(source), charging the external

delay capacitor (CDLY) to 2.5 V.

tDLY =

Vref CDLY

IDLY(source)

=

2.5 CDLY

200 μA

= 12500 CDLY

Figure 5 provides CDLY values for a wide range of time

delays. The Delay pins are pulled low when the respective

input comparator’s noninverting input is less than the

inverting input. The sink current, IDLY(sink), capability of the

Delay pins is ≥ 1.8 mA and is much greater than the typical

200 μA source current, thus enabling a relatively fast delay

capacitor discharge time.

The Overvoltage Drive Output is a current−limited

emitter−follower capable of sourcing 300 mA at a turn−on

slew rate at 2.0 A/μs, ideal for driving “Crowbar” SCR’s.

The Undervoltage Indicator Output is an open−collector,

NPN transistor, capable of sinking 30 mA to provide

sufficient drive for LED’s, small relays or shut−down

circuitry. These current capabilities apply to both channels

operating simultaneously, providing device power

dissipation limits are not exceeded.

The MC3425 has an internal 2.5 V bandgap reference

regulator with an accuracy of ± 4.0% for the basic device.

O.V.

Sense

3

+ Input

Comparator

− O.V.

VCC

8

+

+

200μA

+

+Output

Comparator

− O.V.

U.V.

Sense

4

IH

12.5μA

+ Input

Comparator

− U.V.

+

200μA

−

Output

Comparator

+ U.V.

+

2.5V

Reference

Regulator

O.V.

1

DRV

U.V.

6

IND

Input Section

Note: All voltages and currents are nominal.

52

7

U.V. O.V.

Gnd

DLY DLY

Figure 15. Representative Block Diagram

Output Section

http://onsemi.com

6

Share Link: