NSC LM78S40CN Datasheet

LM78S40
Universal Switching Regulator Subsystem

General Description

The LM78S40 is a monolithic regulator subsystem consisting
of all the active building blocks necessary for switching regu­lator systems. The device consists of a temperature com­pensated voltage reference, a duty-cycle controllable oscilla­tor with an active current limit circuit, an error amplifier, high
current, high voltage output switch, a power diode and an
uncommitted operational amplifier. The device can drive ex­ternal NPN or PNP transistors when currents in excess of

1.5A or voltages in excess of 40V are required. The device
can be used for step-down, step-up or inverting switching
regulators as well as for series pass regulators. It features
wide supply voltage range, low standby power dissipation,
high efficiency and low drift. It is useful for any stand-alone,
low part count switching system and works extremely well in
battery operated systems.

Features

n Step-up, step-down or inverting switching regulators
n Output adjustable from 1.25V to 40V
n Peak currents to 1.5A without external transistors
n Operation from 2.5V to 40V input
n Low standby current drain
n 80 dB line and load regulation
n High gain, high current, independent op amp
n Pulse width modulation with no double pulsing

Block and Connection Diagrams

DS010057-2

16-Lead DIP

DS010057-1

Top View

April 1998

LM78S40 Universal Switching Regulator Subsystem

© 1998 National Semiconductor Corporation DS010057 www.national.com

Ordering Information

Part Number NS Package Temperature Range

LM78S40J/883 J16A Ceramic DIP −55˚C to +125˚C
LM78S40N N16E Molded DIP −40˚C to +125˚C
LM78S40CN N16E Molded DIP 0˚C to +70˚C

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Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Storage Temperature Range

Ceramic DIP −65˚C to +175˚C
Molded DIP −65˚C to +150˚C

Operating Temperature Range

Extended (LM78S40J) −55˚C to +125˚C
Industrial (LM78S40N) −40˚C to +125˚C
Commercial (LM78S40CN) 0˚C to +70˚C

Lead Temperature

Ceramic DIP (Soldering, 60 sec.) 300˚C
Molded DIP (Soldering, 10 sec.) 265˚C

Internal Power Dissipation (Note 2) (Note 3)

16L-Ceramic DIP 1.50W
16L-Molded DIP 1.04W

Input Voltage from V

IN

to GND 40V

Input Voltage from V

+

(Op Amp)

to GND 40V

Common Mode Input Range

(Comparator and Op Amp) −0.3 to V+

Differential Input Voltage

(Note 4)

±

30V

Output Short Circuit

Duration (Op Amp) Continuous

Current from V

REF

10 mA

Voltage from Switch

Collectors to GND 40V

Voltage from Switch

Emitters to GND 40V

Voltage from Switch

Collectors to Emitter 40V
Voltage from Power Diode to GND 40V
Reverse Power Diode Voltage 40V
Current through Power Switch 1.5A
Current through Power Diode 1.5A
ESD Susceptibility (to be determined)

LM78S40
Electrical Characteristics

(Note 5)

T

A

=

Operating temperature range, V

IN

=

5.0V, V

+

(Op Amp)=5.0V, unless otherwise specified.

Symbol Parameter Conditions Min Typ Max Units

GENERAL CHARACTERISTICS

I

CC

Supply Current V

IN

=

5.0V 1.8 3.5 mA

(Op Amp Disconnected) V

IN

=

40V 2.3 5.0 mA

I

CC

Supply Current V

IN

=

5.0V 4.0 mA

(Op Amp Connected) V

IN

=

40V 5.5 mA

REFERENCE SECTION

V

REF

Reference Voltage I

REF

=

1.0 mA Extend −55˚C

<

T

A

<

+125˚C,
Comm 0

<

T

A

<

+70˚C, 1.180 1.245 1.310 V

Indus −40˚C

<

T

A

<

+85˚C

V

R LINE

Reference Voltage V

IN

=

3.0V to V

IN

=

40V, 0.04 0.2 mV/V

Line Regulation I

REF

=

1.0 mA, T

A

=

25˚C

V

R LOAD

Reference Voltage I

REF

=

1.0 mA to I

REF

=

10 mA, 0.2 0.5 mV/mA

Load Regulation T

A

=

25˚C

OSCILLATOR SECTION

I

CHG

Charging Current V

IN

=

5.0V, T

A

=

25˚C 20 50 µA

I

CHG

Charging Current V

IN

=

40V, T

A

=

25˚C 20 70 µA

I

DISCHG

Discharge Current V

IN

=

5.0V, T

A

=

25˚C 150 250 µA

I

DISCHG

Discharge Current V

IN

=

40V, T

A

=

25˚C 150 350 µA

V

OSC

Oscillator Voltage Swing V

IN

=

5.0V, T

A

=

25˚C 0.5 V

t

on/toff

Ratio of Charge/ 6.0 µs/µs
Discharge Time

CURRENT LIMIT SECTION

V

CLS

Current Limit Sense
Voltage

T

A

=

25˚C 250 350 mV

OUTPUT SWITCH SECTION

V

SAT 1

Output Saturation Voltage 1 I

SW

=

1.0A (

Figure 1

) 1.1 1.3 V

V

SAT 2

Output Saturation Voltage 2 I

SW

=

1.0A (

Figure 2

) 0.45 0.7 V

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