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
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
DS008711-1
April 1998
LM1578A/LM2578A/LM3578A
Switching
Regulator
1998 National Semiconductor Corporation
DS008711
www.national.com
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Total Supply Voltage
50V
Collector Output to Ground
-0.3V to +50V
Emitter Output to Ground (Note 2)
-1V to +50V
Power Dissipation (Note 3)
Internally limited
Output Current
750 mA
Storage Temperature
-65C to +150C
Lead Temperature
(soldering, 10 seconds)
260C
Maximum Junction Temperature
150C
ESD Tolerance (Note 4)
2 kV
Operating Ratings
Ambient Temperature Range
LM1578A
-55C
T
A
+125C
LM2578A
-40C
T
A
+85C
LM3578A
0C
T
A
+70C
Junction Temperature Range
LM1578A
-55C
T
J
+150C
LM2578A
-40C
T
J
+125C
LM3578A
0C
T
J
+125C
Electrical Characteristics
These specifications apply for 2V
V
IN
40V (2.2V
V
IN
40V for T
J
-25C), timing capacitor C
T
= 3900 pF, and 25%
duty cycle
75%, unless otherwise specified. Values in standard typeface are for T
J
= 25C; values in boldface type apply for
operation over the specified operating junction temperature range.
LM1578A
LM2578A/
Symbol
Parameter
Conditions
Typical
Limit
LM3578A
Units
(Note 5)
(Note 6)
(Note 11)
Limit
(Note 7)
OSCILLATOR
f
OSC
Frequency
20
kHz
22.4
24
kHz (max)
17.6
16
kHz (min)
f
OSC
/
T
Frequency Drift with
-0.13
%/C
Temperature
Amplitude
550
mV
p-p
REFERENCE/COMPARATOR (Note 8)
V
R
Input Reference
I
1
= I
2
= 0 mA and
1.0
V
Voltage
I
1
= I
2
= 1 mA
1% (Note 9)
1.035/1.050
1.050/1.070 V (max)
0.965/0.950
0.950/0.930
V (min)
V
R
/
V
IN
Input Reference Volt-
I
1
= I
2
= 0 mA and
0.003
%/V
age Line Regulation
I
1
= I
2
= 1 mA
1% (Note 9)
0.01/0.02
0.01/0.02
%/V (max)
I
INV
Inverting Input
I
1
= I
2
= 0 mA, duty cycle = 25%
0.5
A
Current
Level Shift Accuracy
Level Shift Current = 1 mA
1.0
%
5/8
10/13
% (max)
V
R
/
t
Input Reference
100
ppm/1000h
Voltage Long Term
Stability
OUTPUT
V
C
(sat)
Collector Saturation
I
C
= 750 mA pulsed, Emitter
0.7
V
Voltage
grounded
0.85/1.2
0.90/1.2
V (max)
V
E
(sat)
Emitter Saturation
I
O
= 80 mA pulsed,
1.4
V
Voltage
V
IN
= V
C
= 40V
1.6/2.1
1.7/2.0
V (max)
I
CES
Collector Leakage
V
IN
= V
CE
= 40V, Emitter
0.1
A
Current
grounded, Output OFF
50/100
200/250
A (max)
BV
CEO(SUS)
Collector-Emitter
I
SUST
= 0.2A (pulsed), V
IN
= 0
60
V
Sustaining Voltage
50
50
V (min)
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2
Electrical Characteristics
(Continued)
These specifications apply for 2V
V
IN
40V (2.2V
V
IN
40V for T
J
-25C), timing capacitor C
T
= 3900 pF, and 25%
duty cycle
75%, unless otherwise specified. Values in standard typeface are for T
J
= 25C; values in boldface type apply for
operation over the specified operating junction temperature range.
LM1578A
LM2578A/
Symbol
Parameter
Conditions
Typical
Limit
LM3578A
Units
(Note 5)
(Note 6)
(Note 11)
Limit
(Note 7)
CURRENT LIMIT
V
CL
Sense Voltage
Referred to V
IN
or Ground
110
mV
Shutdown Level
(Note 10)
95
80
mV (min)
140
160
mV (max)
V
CL
/
T
Sense Voltage
0.3
%/C
Temperature Drift
I
CL
Sense Bias Current
Referred to V
IN
4.0
A
Referred to ground
0.4
A
DEVICE POWER CONSUMPTION
I
S
Supply Current
Output OFF, V
E
= 0V
2.0
mA
3.0/3.3
3.5/4.0
mA (max)
Output ON, I
C
= 750 mA pulsed,
14
mA
V
E
= 0V
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating
the device beyond its rated operating conditions.
Note 2: For T
J
100C, the Emitter pin voltage should not be driven more than 0.6V below ground (see Application Information).
Note 3: At elevated temperatures, devices must be derated based on package thermal resistance. The device in the TO-99 package must be derated at 150C/W,
junction to ambient, or 45C/W, junction to case. The device in the 8-pin DIP must be derated at 95C/W, junction to ambient. The device in the surface-mount package
must be derated at 150C/W, junction-to-ambient.
Note 4: Human body model, 1.5 k
in series with 100 pF.
Note 5: Typical values are for T
J
= 25C and represent the most likely parametric norm.
Note 6: All limits guaranteed and 100% production tested at room temperature (standard type face) and at temperature extremes (bold type face). All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Note 7: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). Room temperature limits are 100% production
tested. Limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate AOQL.
Note 8: Input terminals are protected from accidental shorts to ground but if external voltages higher than the reference voltage are applied, excessive current will
flow and should be limited to less than 5 mA.
Note 9: I
1
and I
2
are the external sink currents at the inputs (refer to Test Circuit).
Note 10: Connection of a 10 k
resistor from pin 1 to pin 4 will drive the duty cycle to its maximum, typically 90%. Applying the minimum Current Limit Sense Voltage
to pin 7 will not reduce the duty cycle to less than 50%. Applying the maximum Current Limit Sense Voltage to pin 7 is certain to reduce the duty cycle below 50%.
Increasing this voltage by 15 mV may be required to reduce the duty cycle to 0%, when the Collector output swing is 40V or greater (see Ground-Referred Current
Limit Sense Voltage typical curve).
Note 11: A military RETS specification is available on request. At the time of printing, the LM1578A RETS spec complied with the boldface limits in this column. The
LM1578AH may also be procured as a Standard Military Drawing.
3
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Connection Diagram and Ordering Information
Typical Performance Characteristics
Metal Can
DS008711-28
Top View
Order Number LM1578AH/883 or SMD #5962-8958602
See NS Package Number H08C
Dual-In-Line Package
DS008711-29
Order Number LM3578AM, LM2578AN or LM3578AN
See NS Package Number M08A or N08E
Oscillator Frequency Change
with Temperature
DS008711-32
Oscillator Voltage Swing
DS008711-33
Input Reference Voltage
Drift with Temperature
DS008711-34
Collector Saturation Voltage
(Sinking Current,
Emitter Grounded)
DS008711-35
Emitter Saturation Voltage
(Sourcing Current,
Collector at V
in
)
DS008711-36
Ground Referred
Current Limit Sense Voltage
DS008711-37
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4
Typical Performance Characteristics
(Continued)
Test Circuit
*
Parameter tests can be made using the test circuit shown.
Select the desired V
in
, collector voltage and duty cycle with
adjustable power supplies. A digital volt meter with an input
resistance greater than 100 M
should be used to measure
the following:
Input Reference Voltage to Ground; S1 in either position.
Level Shift Accuracy (%) = (T
P3
(V)/1V) x 100%; S1 at I
1
= I
2
= 1 mA
Input Current (mA) = (1V - T
p3
(V))/1 M
: S1 at I
1
= I
2
=
0 mA.
Oscillator parameters can be measured at T
p4
using a fre-
quency counter or an oscilloscope.
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 V
in
terminal. Set the duty cycle to 90% and monitor test
point T
P5
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 I
1
= I
2
= 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.
Current Limit Sense Voltage
Drift with Temperature
DS008711-38
Current Limit Response Time
for Various Over Drives
DS008711-39
Current Limit Sense Voltage
vs Supply Voltage
DS008711-40
Supply Current
DS008711-41
Supply Current
DS008711-42
Collector Current with
Emitter Output Below Ground
DS008711-43
5
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