LM2578A/LM3578A
Switching Regulator
General Description
The LM2578A 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 LM2578A 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 LM2578A has an on board oscillator, which sets the
switching frequency with a single external capacitor from
<
1
Hz to 100 kHz (typical).
The LM2578A is an improved version of the LM2578, 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
Connection Diagram and Ordering Information
Dual-In-Line Package
00871129
Order Number LM3578AM, LM2578AN or LM3578AN
See NS Package Number M08A or N08E
February 2005
LM2578A/LM3578A
Switching
Regulator
2005 National Semiconductor Corporation
DS008711
www.national.com
Functional Diagram
00871101
LM2578A/LM3578A
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2
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
LM2578A
-40C
T
A
+85C
LM3578A
0C
T
A
+70C
Junction Temperature Range
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.
LM2578A/
Symbol
Parameter
Conditions
Typical
LM3578A
Units
(Note 5)
Limit (Note 6)
OSCILLATOR
f
OSC
Frequency
20
kHz
24
kHz (max)
16
kHz (min)
f
OSC
/
T
Frequency Drift with Temperature
-0.13
%/C
Amplitude
550
mV
p-p
REFERENCE/COMPARATOR (Note 7)
V
R
Input Reference
I
1
= I
2
= 0 mA and
1.0
V
Voltage
I
1
= I
2
= 1 mA
1% (Note 8)
1.050/1.070
V (max)
0.950/0.930
V (min)
V
R
/
V
IN
Input Reference Voltage Line
Regulation
I
1
= I
2
= 0 mA and
0.003
%/V
I
1
= I
2
= 1 mA
1% (Note 8)
0.01/0.02
%/V (max)
I
INV
Inverting Input Current
I
1
= I
2
= 0 mA, duty cycle = 25%
0.5
A
Level Shift Accuracy
Level Shift Current = 1 mA
1.0
%
10/13
% (max)
V
R
/
t
Input Reference Voltage Long Term
Stability
100
ppm/1000h
OUTPUT
V
C
(sat)
Collector Saturation Voltage
I
C
= 750 mA pulsed, Emitter
grounded
0.7
V
0.90/1.2
V (max)
V
E
(sat)
Emitter Saturation Voltage
I
O
= 80 mA pulsed,
1.4
V
V
IN
= V
C
= 40V
1.7/2.0
V (max)
I
CES
Collector Leakage Current
V
IN
= V
CE
= 40V, Emitter grounded,
Output OFF
0.1
A
200/250
A (max)
BV
CEO(SUS)
Collector-Emitter Sustaining Voltage I
SUST
= 0.2A (pulsed), V
IN
= 0
60
V
50
V (min)
CURRENT LIMIT
V
CL
Sense Voltage Shutdown Level
Referred to V
IN
or Ground
110
mV
(Note 9)
80
mV (min)
160
mV (max)
LM2578A/LM3578A
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3
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.
LM2578A/
Symbol
Parameter
Conditions
Typical
LM3578A
Units
(Note 5)
Limit (Note 6)
CURRENT LIMIT
V
CL
/
T
Sense Voltage Temperature Drift
0.3
%/C
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
3.5/4.0
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 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 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 7: 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 8: I
1
and I
2
are the external sink currents at the inputs (refer to Test Circuit).
Note 9: 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).
Typical Performance Characteristics
Oscillator Frequency Change
with Temperature
Oscillator Voltage Swing
00871132
00871133
LM2578A/LM3578A
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4
Typical Performance Characteristics
(Continued)
Input Reference Voltage
Drift with Temperature
Collector Saturation Voltage
(Sinking Current,
Emitter Grounded)
00871134
00871135
Emitter Saturation Voltage
(Sourcing Current,
Collector at V
in
)
Ground Referred
Current Limit Sense Voltage
00871136
00871137
Current Limit Sense Voltage
Drift with Temperature
Current Limit Response Time
for Various Over Drives
00871138
00871139
LM2578A/LM3578A
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