L4974 Ver la hoja de datos (PDF) - STMicroelectronics

Número de pieza

componentes Descripción

Fabricante

L4974

3.5A SWITCHING REGULATOR

STMicroelectronics 

PIN FUNCTIONS

No

Name

1 BOOTSTRAP

2 RESET DELAY

3 RESET OUT

4 RESET INPUT

5, 6

15, 16

7

8

GROUND

FREQUENCY

COMPENSATION

SOFT START

9 FEEDBACK INPUT

10 SYNC INPUT

11

12, 19

13

14

17

SUPPLY VOLTAGE

N.C.

Vref

Vstart

OSCILLATOR

18 OSCILLATOR

20 OUTPUT

L4974A

F unctio n

A Cboot capacitor connected between this terminal and the output allows to drive

properly the internal D-MOS transistor.

A Cd capacitor connected between this terminal and ground determines the reset

signal delay time.

Open Collector Reset/power Fail Signal Output. This output is high when the supply

and the output voltages are safe.

Input of Power Fail Circuit. The threshold is 5.1V. It may be connected via a divider

to the input for power fail function. It mustbe connected to the pin 14 an external 30KΩ

resistor when power fail signal not required.

Common Ground Terminal

A series RC network connected between this terminal and ground determines the

regulation loop gain characteristics.

Soft Start Time Constant. A capacitor is connected between thi sterminal and ground

to define the soft start time constant.

The Feedback Terminal of the Regulation Loop. The output is connected directly to

this terminal for 5.1V operation; It is connected via a divider for higher voltages.

Multiple L4974A’s are synchronized by connecting pin 10 inputs together or via an

external syncr. pulse.

Unregulated Input Voltage.

Not Connected.

5.1V Vref Device Reference Voltage.

Internal Start-up Circuit to Drive the Power Stage.

Rosc. External resistor connected to ground determines the constant charging current

of Cosc.

Cosc. External capacitor connected to ground determines (with Rosc) the switching

frequency.

Regulator Output.

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