THERMAL DATA

Symbol

Parameter

DIP 20

SO 20

Unit

Thermal Resistance Junction-ambient

80

120

°C/W

PIN FUNCTIONS

N.

Name

Description

1

P-GND

Power ground.

2

IPK

L4981A peak current limiting. A current limitation is obtained using a single resistor connected

between Pin 2 and the sense resistor. To have a better precision another resistor between Pin

2 and a reference voltage (Pin 11) must be added.

L4981B peak current limiting. A precise current limitation is obtained using two external

resistor only. These resistors must be connected between the sense resistor, Pin 2 and the

reference voltage.

3

OVP

Overvoltage protection. At this input are compared an internal precise 5.1V (typ) voltage

reference with a sample of the boost output voltage obtained via a resistive voltage divider in

order to limit the maximum output peak voltage.

4

IAC

Input for the AC current. An input current proportional to the rectified mains voltage generates,

via a multiplier, the current reference for the current amplifier.

5

CA-OUT

Current amplifier output. An external RC network determinates the loop gain.

6

LFF

Load feedforward; this voltage input pin allows to modify the multiplier output current

proportionally to the load, in order to give a faster response versus load transient. The best

control is obtained working between 1.5V and 5.3V. If this function is not used, connect this pin

to the voltage reference (pin = 11).

7

VRMS

Input for proportional RMS line voltage. the VRMS input compesates the line voltage changes.

Connecting a low pass filter between the rectified line and the pin 7, a DC voltage proportional

to the input line RMS voltage is obtained. The best control is reached using input voltage

between 1.5V and 5.5V. If this function is not used connect this pin to the voltage reference

(pin = 11).

8

MULT-OUT

Multiplier output. This pin common to the multiplier output and the current amplifier N.I. input is

Current amplifier inverting input. Care must be taken to avoid this pin goes down -0.5V.

10

S-GND

Signal ground.

11

Output reference voltage (typ = 5.1V).Voltage refence at

± 2% of accuracy externally available,

it’s internally current limited and can deliver an output current up to 10mA.

12

SS

A capacitor connected to ground defines the soft start time. An internal current generator

delivering 100

µA (typ) charges the external capacitor defining the soft start time constant. An

internal MOS discharge, the external soft start capacitor both in overvoltage and UVLO

conditions.

13

VA-OUT

Error amplifier output, an RC network fixes the voltage loop gain characteristics.

14

VFEED

Voltage error amplifier inverting input. This feedback input is connected via a voltage divider to

the boost output voltage.

15

P-UVLO

Programmable under voltage lock out threshold input. A voltage divider between supply

voltage and GND can be connected in order to program the turn on threshold.

16

SYNC

(L4981A)

This synchronization input/output pin is CMOS logic compatible. Operating as SYNC in, a

rectangular wave must be applied at this pin. Opearting as SYNC out, a rectangular clock

pulse train is available to synchronize other devices.

FREQ-MOD

(L4981B)

Frequency modulation current input. An external resistor must be connected between pin 16

and the rectified line voltage in order to modulate the oscillator frequency. Connecting pin 16 to

17

18

An external capacitor connected to GND fixes the switching frequency.

19

Supply input voltage.

20

GDRV

Output gate driver. Bipolar and DMOS transistors totem pole output stage can deliver peak

current in excess 1A useful to drive MOSFET or IGBT power stages.

L4981A - L4981B

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