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PDF LM1578 Data sheet ( Hoja de datos )
| Número de pieza | LM1578 | |
| Descripción | Switching Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM1578 (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
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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 Vin 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 Inverting and non-inverting feedback inputs
n 1.0V reference at inputs
n Operates from supply voltages of 2V to 40V
n Output current up to 750 mA, saturation less than 0.9V
n Current limit and thermal shut down
n 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
© 1998 National Semiconductor Corporation DS008711
DS008711-1
www.national.com
1 page  
Typical Performance Characteristics (Continued)
Current Limit Sense Voltage
Drift with Temperature
Current Limit Response Time
for Various Over Drives
Current Limit Sense Voltage
vs Supply Voltage
Supply Current
DS008711-38
Supply Current
DS008711-39
DS008711-40
Collector Current with
Emitter Output Below Ground
DS008711-41
Test Circuit*
Parameter tests can be made using the test circuit shown.
Select the desired Vin, collector voltage and duty cycle with
adjustable power supplies. A digital volt meter with an input
resistance greater than 100 MΩ should be used to measure
the following:
Input Reference Voltage to Ground; S1 in either position.
Level Shift Accuracy (%) = (TP3(V)/1V) x 100%; S1 at I1 = I2
= 1 mA
Input Current (mA) = (1V − Tp3 (V))/1 MΩ: S1 at I1 = I2 =
0 mA.
Oscillator parameters can be measured at Tp4 using a fre-
quency counter or an oscilloscope.
DS008711-42
DS008711-43
The Current Limit Sense Voltage is measured by connecting
an adjustable 0-to-1V floating power supply in series with the
current limit terminal and referring it to either the ground or
the Vin terminal. Set the duty cycle to 90% and monitor test
point TP5 while adjusting the floating power supply voltage
until the LM1578A’s duty cycle just reaches 0%. This voltage
is the Current Limit Sense Voltage.
The Supply Current should be measured with the duty cycle
at 0% and S1 in the I1 = I2 = 0 mA position.
*LM1578A specifications are measured using automated
test equipment. This circuit is provided for the customer’s
convenience when checking parameters. Due to possible
variations in testing conditions, the measured values from
these testing procedures may not match those of the factory.
5 www.national.com
5 Page 
Typical Applications (Continued)
11 www.national.com
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LM1578.PDF ] | |
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