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National Semiconductor
National Semiconductor

LM3578 Datasheet

Switching Regulator


LM3578 Datasheet Preview


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
Page 1

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
Collector Output to Ground
Emitter Output to Ground (Note 2)
Power Dissipation (Note 3)
Output Current
Storage Temperature
Lead Temperature
(soldering, 10 seconds)
Maximum Junction Temperature
50V
−0.3V to +50V
−1V to +50V
Internally limited
750 mA
−65˚C to +150˚C
260˚C
150˚C
ESD Tolerance (Note 4)
Operating Ratings
Ambient Temperature Range
LM1578A
LM2578A
LM3578A
Junction Temperature Range
LM1578A
LM2578A
LM3578A
2 kV
−55˚C TA +125˚C
−40˚C TA +85˚C
0˚C TA +70˚C
−55˚C TJ +150˚C
−40˚C TJ +125˚C
0˚C TJ +125˚C
Electrical Characteristics
These specifications apply for 2V VIN 40V (2.2V VIN 40V for TJ −25˚C), timing capacitor CT = 3900 pF, and 25%
duty cycle 75%, unless otherwise specified. Values in standard typeface are for TJ = 25˚C; 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
fOSC
Frequency
20
22.4
kHz
24 kHz (max)
17.6
16 kHz (min)
fOSC/T
Frequency Drift with
Temperature
−0.13
%/˚C
Amplitude
REFERENCE/COMPARATOR (Note 8)
550 mVp-p
VR
Input Reference
I1 = I2 = 0 mA and
1.0
V
Voltage
I1 = I2 = 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)
VR/VIN
IINV
Input Reference Volt-
age Line Regulation
Inverting Input
Current
I1 = I2 = 0 mA and
I1 = I2 = 1 mA ±1% (Note 9)
I1 = I2 = 0 mA, duty cycle = 25%
0.003
0.5
0.01/0.02
0.01/0.02
%/V
%/V (max)
µA
Level Shift Accuracy Level Shift Current = 1 mA
1.0
%
5/8 10/13 % (max)
VR/t
Input Reference
Voltage Long Term
100 ppm/1000h
Stability
OUTPUT
VC (sat)
Collector Saturation
Voltage
IC = 750 mA pulsed, Emitter
grounded
0.7 V
0.85/1.2
0.90/1.2 V (max)
VE (sat)
ICES
Emitter Saturation
Voltage
Collector Leakage
Current
IO = 80 mA pulsed,
VIN = VC = 40V
VIN = VCE = 40V, Emitter
grounded, Output OFF
1.4 V
1.6/2.1
1.7/2.0 V (max)
0.1 µA
50/100
200/250 µA (max)
BVCEO(SUS) Collector-Emitter
Sustaining Voltage
ISUST = 0.2A (pulsed), VIN = 0
60
50
V
50 V (min)
www.national.com
2
Page 2

Electrical Characteristics (Continued)
These specifications apply for 2V
duty cycle 75%, unless otherwise
VIN 40V
specified.
(2.2V VIN 40V
Values in standard
for TJ −25˚C),
typeface are for
tTimJ i=ng2c5a˚Cpa; cviatolureCsTin=
3900 pF,
boldface
and
type
25%
apply for
operation over the specified operating junction temperature range.
LM1578A LM2578A/
Symbol
Parameter
Conditions
Typical
(Note 5)
Limit
(Note 6)
(Note 11)
LM3578A
Limit
(Note 7)
Units
CURRENT LIMIT
VCL Sense Voltage
Shutdown Level
Referred to VIN or Ground
(Note 10)
110
95
mV
80 mV (min)
140 160 mV (max)
VCL/T
Sense Voltage
Temperature Drift
0.3 %/˚C
ICL
Sense Bias Current
Referred to VIN
Referred to ground
4.0
0.4
µA
µA
DEVICE POWER CONSUMPTION
IS Supply Current
Output OFF, VE = 0V
Output ON, IC = 750 mA pulsed,
VE = 0V
2.0
14
3.0/3.3
3.5/4.0
mA
mA (max)
mA
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 TJ 100˚C, 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 150˚C/W,
junction to ambient, or 45˚C/W, junction to case. The device in the 8-pin DIP must be derated at 95˚C/W, junction to ambient. The device in the surface-mount package
must be derated at 150˚C/W, junction-to-ambient.
Note 4: Human body model, 1.5 kin series with 100 pF.
Note 5: Typical values are for TJ = 25˚C 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: I1 and I2 are the external sink currents at the inputs (refer to Test Circuit).
Note 10: Connection of a 10 kresistor 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 www.national.com
Page 3
Part Number LM3578
Manufactur National Semiconductor
Description Switching Regulator
Total Page 18 Pages
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