LM1578A/LM2578A/LM3578A Switching Regulator
April 1998
LM1578A/LM2578A/LM3578A
Switching Regulator
General Description
The LM1578A is a switching regulator which can easily be
set up for such DC-to-DC voltage conversion circuits as the
buck, boost, and inverting configurations. The LM1578A fea-
tures a unique comparator input stage which not only has
separate pins for both the inverting and non-inverting inputs,
but also provides an internal 1.0V reference to each input,
thereby simplifying circuit design and p.c. board layout. The
output can switch up to 750 mA and has output pins for its
collector and emitter to promote design flexibility. An external
current limit terminal may be referenced to either the ground
or the V
in
terminal, depending upon the application. In addi-
tion, the LM1578A has an on board oscillator, which sets the
switching frequency with a single external capacitor from
<
1
Hz to 100 kHz (typical).
The LM1578A is an improved version of the LM1578, offer-
ing higher maximum ratings for the total supply voltage and
output transistor emitter and collector voltages.
Features
n
n
n
n
n
n
Inverting and non-inverting feedback inputs
1.0V reference at inputs
Operates from supply voltages of 2V to 40V
Output current up to 750 mA, saturation less than 0.9V
Current limit and thermal shut down
Duty cycle up to 90%
Applications
n
Switching regulators in buck, boost, inverting, and
single-ended transformer configurations
n
Motor speed control
n
Lamp flasher
Functional Diagram
DS008711-1
© 1998 National Semiconductor Corporation
DS008711
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