National Semiconductor LM1578A, LM2578A, LM3578A Technical data

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LM1578A/LM2578A/LM3578A Switching Regulator
LM1578A/LM2578A/LM3578A Switching Regulator
April 1998
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 fea­tures 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 tion, the LM1578A has an on board oscillator,which sets the switching frequency with a single external capacitor from Hz to 100 kHz (typical).
The LM1578A is an improved version of the LM1578, offer­ing higher maximum ratings for the total supply voltage and output transistor emitter and collector voltages.
terminal, depending upon the application. In addi-
in
<
Functional Diagram
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
1
n Lamp flasher
DS008711-1
© 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 −65˚C to +150˚C Lead Temperature
(soldering, 10 seconds) 260˚C
Maximum Junction Temperature 150˚C
ESD Tolerance (Note 4) 2 kV
Operating Ratings
Ambient Temperature Range
LM1578A −55˚C T LM2578A −40˚C T LM3578A 0˚C T
Junction Temperature Range
LM1578A −55˚C T LM2578A −40˚C T LM3578A 0˚C T
+125˚C
A
+85˚C
A
+70˚C
A
+150˚C
J
+125˚C
J
+125˚C
J
Electrical Characteristics
These specifications apply for 2V VIN≤ 40V (2.2V ≤ VIN≤ 40V for TJ≤ −25˚C), timing capacitor C duty cycle 75%, unless otherwise specified. Values in standard typeface are for T operation over the specified operating junction temperature range.
=
25˚C; values in boldface type apply for
J
LM1578A LM2578A/
Symbol Parameter Conditions Typical Limit LM3578A Units
(Note 5) (Note 6)
(Note 11)
OSCILLATOR
f
OSC
f
OSC
Frequency 20 kHz
/T Frequency Drift with −0.13
Temperature Amplitude 550 mV
REFERENCE/COMPARATOR (Note 8)
=
V
R
Input Reference I Voltage I
=
I
0 mA and 1.0 V
1
2
=
=
±
I
1
2
1%(Note 9) 1.035/1.050 1.050/1.070 V (max)
1mA
0.965/0.950 0.950/0.930 V (min)
=
V
I
/V
R
Input Reference Volt- I
IN
age Line Regulation I
INV
Inverting Input I
=
I
0 mA and 0.003
1
2
=
=
±
I
1
2
=
=
I
1
2
1%(Note 9) 0.01/0.02 0.01/0.02%/V (max)
1mA 0 mA, duty cycle=25
%
0.5 µA Current Level Shift Accuracy Level Shift Current=1 mA 1.0
V
/t Input Reference 100 ppm/1000h
R
Voltage Long Term Stability
OUTPUT
V
(sat) Collector Saturation I
C
=
750 mA pulsed, Emitter 0.7 V
C
Voltage grounded 0.85/1.2 0.90/1.2 V (max)
V
(sat) Emitter Saturation I
E
Voltage V
I
CES
Collector Leakage V
=
80 mA pulsed, 1.4 V
O
=
=
V
IN IN
40V 1.6/2.1 1.7/2.0 V (max)
C
=
=
V
40V, Emitter 0.1 µA
CE
Current grounded, Output OFF 50/100 200/250 µA (max)
BV
CEO(SUS)
Collector-Emitter I
SUST
=
0.2A (pulsed), V
=
060 V
IN
Sustaining Voltage 50 50 V (min)
=
3900 pF, and 25%≤
T
Limit
(Note 7)
22.4 24 kHz (max)
17.6 16 kHz (min) %
/˚C
%
/V
%
5/8 10/13
%
(max)
p-p
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Electrical Characteristics (Continued)
These specifications apply for 2V VIN≤ 40V (2.2V ≤ VIN≤ 40V for TJ≤ −25˚C), timing capacitor C duty cycle 75%, unless otherwise specified. Values in standard typeface are for T operation over the specified operating junction temperature range.
=
25˚C; values in boldface type apply for
J
LM1578A LM2578A/
Symbol Parameter Conditions Typical Limit LM3578A Units
(Note 5) (Note 6)
(Note 11)
CURRENT LIMIT
V
Sense Voltage Referred to VINor Ground 110 mV
CL
Shutdown Level (Note 10) 95 80 mV (min)
V
/T Sense Voltage 0.3
CL
Temperature Drift
I
CL
Sense Bias Current Referred to V
IN
4.0 µA
Referred to ground 0.4 µA
DEVICE POWER CONSUMPTION
I
S
Supply Current Output OFF, V
=
0V 2.0 mA
E
3.0/3.3 3.5/4.0 mA (max)
0V
=
750 mA pulsed, 14 mA
C
Output ON, I
=
V
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC andAC electrical specifications do not apply when operating the device beyond its rated operating conditions.
Note 2: For T 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 tocase. Thedevice inthe 8-pinDIP must be deratedat 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 T Note 6: All limits guaranteed and 100%production tested at room temperature (standard type face) and at temperatureextremes (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 temperatureextremes are guaranteed via correlationusing standard Statistical Quality Control (SQC) methods.All limitsare used to calculateAOQL. 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 Note 10: Connection ofa 10 kresistor frompin 1 to pin 4will drive the duty cycleto 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: Amilitary RETS specification is available on request.At the time of printing, the LM1578ARETS spec complied with the boldface limits in this column. The LM1578AH may also be procured as a Standard Military Drawing.
100˚C, the Emitter pin voltage should not be driven more than 0.6V below ground (see Application Information).
J
=
25˚C and represent the most likely parametric norm.
J
and I2are the external sink currents at the inputs (refer to Test Circuit).
1
E
=
3900 pF, and 25%≤
T
Limit
(Note 7)
140 160 mV (max)
%
/˚C
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Connection Diagram and Ordering Information
Metal Can
DS008711-28
Top View
Order Number LM1578AH/883 or SMD
#
5962-8958602
See NS Package Number H08C
Typical Performance Characteristics
Oscillator Frequency Change with Temperature
Oscillator Voltage Swing
Dual-In-Line Package
DS008711-29
Order Number LM3578AM, LM2578AN or LM3578AN
See NS Package Number M08A or N08E
Input Reference Voltage Drift with Temperature
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Collector Saturation Voltage (Sinking Current, Emitter Grounded)
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Emitter Saturation Voltage (Sourcing Current, Collector at V
)
in
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DS008711-36
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Ground Referred Current Limit Sense Voltage
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Typical Performance Characteristics (Continued)
Current Limit Sense Voltage Drift with Temperature
Supply Current
Test Circuit
*
DS008711-38
DS008711-41
Current Limit Response Time for Various Over Drives
Supply Current
Parameter tests can be made using the test circuit shown. Select the desired V adjustable power supplies. A digital volt meter with an input
, collector voltage and duty cycle with
in
resistance greater than 100 Mshould be used to measure the following:
Input Reference Voltage to Ground; S1 in either position. Level Shift Accuracy (%)=(T
=
1mA
Input Current (mA)=(1V − T 0 mA.
(V)/1V) x 100%;S1atI
P3
(V))/1 M:S1atI
p3
Oscillator parameters can be measured at T quency counter or an oscilloscope.
p4
=
1
=
I
1
2
using a fre-
Current Limit Sense Voltage vs Supply Voltage
DS008711-39
Collector Current with Emitter Output Below Ground
DS008711-42
terminal. Set the duty cycle to 90%and monitor test
in
point T until the LM1578A’s duty cycle just reaches 0%. This voltage
while adjusting the floating power supply voltage
P5
is the Current Limit Sense Voltage. The Supply Current should be measured with the duty cycle
I
at 0%and S1 in the I
2
*
=
LM1578A specifications are measured using automated
test equipment. This circuit is provided for the customer’s
=
1
=
I
0 mA position.
2
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.
DS008711-40
DS008711-43
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Test Circuit
*
(Continued)
Op amp supplies are±15V DVM input resistance
*
LM1578 max duty cycle is 90
>
100 M
%
Definition of Terms
Input Reference Voltage: The voltage (referred to ground)
that must be applied to either the inverting or non-inverting input to cause the regulator switch to change state (ON or OFF).
Input Level Shift Accuracy: This specification determines the output voltagetoleranceof a regulator whose output con­trol depends on drawing equal currents from the inverting and non-inverting inputs (see the Inverting Regulator of
ure 21
, and the RS-232 Line Driver Power Supply of
23
).
Level Shift Accuracy is tested by using two equal-value re­sistors to draw current from the inverting and non-inverting input terminals, then measuring the percentage difference in the voltages across the resistors that produces a controlled duty cycle at the switch output.
Collector Saturation Voltage: With the inverting input ter­minal grounded thru a 10 kresistor and the output transis­tor’s emitter connected to ground, the Collector Saturation­Voltage is the collector-to-emitter voltage for a given collector current.
Emitter Saturation Voltage: With the inverting input termi­nal grounded thru a 10kresistor and the output transistor’s collector connected to V the collector-to-emitter voltage for a given emitter current.
, the Emitter Saturation Voltage is
in
Collector Emitter Sustaining Voltage: The collector-emitter breakdown voltage of the output transistor, measured at a specified current.
Fig-
Figure
DS008711-3
Current Limit Sense Voltage: The voltage at the Current Limit pin, referred to either the supply or the ground terminal, which (via logic circuitry) will cause the output transistor to turn OFF and resets cycle-by-cycle at the oscillator fre­quency.
Current Limit Sense Current: The bias current for the Cur­rent Limit terminal with the applied voltage equal to the Cur­rent Limit Sense Voltage.
Supply Current: The IC power supply current, excluding the current drawn through the output transistor, with the oscilla­tor operating.
Functional Description
Acontrol signal, usually representing output voltage, fed into the LM1578A’s comparator is compared with an internally-generated reference. The resulting error signal and the oscillator’s output are fed to a logic network which determines when the output transistor will be turned ON or OFF. The following isa brief description of the subsections of the LM1578A.
COMPARATOR INPUT STAGE
The LM1578A’s comparator input stage is unique in that both the inverting and non-inverting inputs are available to the user, and both contain a 1.0V reference. This is accom­plished as follows: A 1.0V reference is fed into a modified voltage follower circuit (see FUNCTIONAL DIAGRAM). When both input pins are open, no current flows through R1
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