NSC LM494CN Pulse width modulated control circuit Datasheet

LM494
Pulse Width Modulated Control Circuit
General Description
Features
The LM494 is a monolithic integrated circuit which includes
all the necessary building blocks for the design of pulse
width modulated (PWM) switching power supplies, including
push-pull, bridge and series configurations. The device can
operate at switching frequencies between 1.0 kHz and
300 kHz and output voltages up to 40V. The operating temperature range specified for the LM494C is 0§ C to 70§ C and
for the LM494V is b40§ C to a 85§ C.
Y
Y
Y
Y
Y
Y
Y
Uncommitted output transistors capable of 200 mA
source or sink
On-chip error amplifiers
On-chip 5.0V reference
Internal protection from double pulsing of outputs with
narrow pulse widths or with supply voltages below
specified limits
Dead time control comparator
Output control selects single ended or push-pull operation
Easily synchronized (slaved) to other circuits
Block Diagram
TL/H/10056 – 2
Connection Diagram
Ordering Information
16-Lead DIP
Device
Code
Package
Code
Package
Description
LM494IN
LM494CJ
LM494CN
N16A
J16A
N16A
Molded DIP
Ceramic DIP
Molded DIP
TL/H/10056 – 1
Top View
C1995 National Semiconductor Corporation
TL/H/10056
RRD-B30M115/Printed in U. S. A.
LM494 Pulse Width Modulated Control Circuit
June 1989
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Output Collector Voltage
Storage Temperature Range
Ceramic DIP
Molded DIP
ESD Susceptibility
Operating Temperature Range
Industrial (LM494I)
Commercial (LM494C)
b 65§ C to a 175§ C
b 65§ C to a 150§ C
Internal Power Dissipation (Notes 1, 2)
16L-Ceramic DIP
16L-Molded DIP
Supply Voltage
Voltage from Any Lead to Ground
(except Lead 8 and Lead 11)
250 mA
(to be determined)
Recommended Operating
Conditions
b 40§ C to a 85§ C
0§ C to a 70§ C
Lead Temperature
Ceramic DIP (Soldering, 60 sec.)
Molded DIP (Soldering, 10 sec.)
42V
Peak Collector Current
(IC1 and IC2)
Power Supply Voltage (VCC)
Voltage on Any Lead
except Leads 8 and 11
(Referenced to Ground) (VI)
300§ C
265§ C
7.0V to 40V
Output Voltage Collector (VC1, VC2)
Output Collector Current (IC1, IC2)
Timing Capacitor (CT)
Timing Resistor (RT)
Oscillator Frequency (fOSC)
1.50W
1.04W
42V
VCC a 0.3V
b 0.3V to VCC a 0.3V
b 0.3V to 40V
200 mA
470 pF to 10 mF
1.8 kX to 500 kX
1.0 kHz to 300 kHz
LM494
Electrical Characteristics TA e 0§ C to a 70§ C for the LM494C, TA e b40§ C to a 85§ C for the LM494I, VCC e
15V, fOSC e 10 kHz, unless otherwise specified
Symbol
Parameter
Conditions
Min
Typ
Max
Units
4.75
REFERENCE SECTION
VREF
Reference Voltage (Note 3)
IREF e 1.0 mA
5.0
5.25
V
RegLINE
Line Regulation of
Reference Voltage
7.0V s VCC s 40V
2.0
25
mV
TCVREF
Temperature Coefficient of
Reference Voltage
0§ C s TA s 70§ C
0.01
0.03
%/§ C
RegLOAD
Load Regulation of
Reference Voltage
1.0 mA s IREF s 10 mA
1.0
15
mV
IOS
Output Short Circuit Current
VREF e 0V
35
50
0§ C s TA s a 70§ C
10
b 40§ C s TA s a 85§ C
mA
35
OSCILLATOR SECTION
fOSC
Oscillator Frequency
(Figure 10)
CT e 0.01 mF,
RT e 12 kX
DfOSC
Oscillator Frequency Change
CT e 0.01 mF,
RT e 12 kX
10
kHz
0§ C s TA s a 70§ C
2.0
b 40§ C s TA s a 85§ C
2.0
%
DEAD TIME CONTROL SECTION
IIB (DT)
Input Bias Current
VCC e 15V, 0V s V4 s 5.25V
DC(Max)
Maximum Duty Cycle,
Each Output
VCC e 15V, Lead 4 e 0V,
Output Control e VREF
VTH(in)
Input Threshold Voltage
b 2.0
45
Zero Duty Cycle
mA
%
3.0
Maximum Duty Cycle
b 10
3.3
V
0
ERROR AMPLIFIER SECTIONS
VIO
Input Offset Voltage
V3 e 2.5V
2.0
10
IIO
Input Offset Current
V3 e 2.5V
25
250
nA
IIB
Input Bias Current
V3 e 2.5V
0.2
1.0
mA
VICR
Input Common Mode
Voltage Range
7.0V s VCC s 40V
b 0.3
VCC
V
AVS
Large Signal Voltage Gain
0.5V s V3 s 3.5V
60
BW
Bandwidth
2
mV
74
dB
650
kHz
LM494
Electrical Characteristics TA e 0§ C to a 70§ C for the LM494C, TA e b40§ C to a 85§ C for the LM494I,
VCC e 15V, fOSC e 10 kHz, unless otherwise specified (Continued)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
4.0
4.5
V
PWM COMPARATOR SECTION (Figure 9)
VTHI
Inhibit Threshold Voltage
Zero Duty Cycle
IO b
Output Sink Current
(Note 4)
0.5V s V3 s 3.5V
IO a
Output Source Current
(Note 4)
0.5V s V3 s 3.5V
b 0.2
b 0.6
mA
2.0
mA
OUTPUT SECTION
VCE(sat)
Output Saturation
Voltage Common Emitter
Configuration (Figure 3)
VE e 0V,
IC e 200 mA
0§ C s TA s a 70§ C
b 40§ C s TA s a 85§ C
Emitter Follower
Configuration (Figure 4)
VC e 15V, IE e 200 mA
1.5
2.5
IC(off)
Collector Off-State Current
VCC e 40V, VCE e 40V
2.0
100
mA
IE(off)
Emitter Off-State Current
VCC e VC e 40V,
VE e 0
b 100
mA
0.4
V
1.1
1.3
V
0§ C s TA s a 70§ C,
b 40§ C s TA s a 85§ C
OUTPUT CONTROL (Figure 6)
VOCL
VOCH
Output Control Voltage
Required for Single Ended or
Parallel Output Operation
Output Control Voltage
Required for Push-Pull
Operation
2.4
V
TOTAL DEVICE
ICC
Standby Power Supply Current
6.0
10
Rise Time of Output Voltage
Common Emitter Configuration
(Figure 3)
100
200
Emitter Follower Configuration
(Figure 4)
100
200
Fall Time of Output Voltage
Common Emitter Configuration
(Figure 3)
25
100
Emitter Follower Configuration
(Figure 4)
40
mA
OUTPUT AC CHARACTERISTICS Use Recommended Operating Conditions with TA e 25§ C
tr
tf
ns
ns
100
Note 1: TJ Max e 150§ C for the Molded DIP, and 175§ C for the Ceramic DIP.
Note 2: Ratings apply to ambient temperature at 25§ C. Above this temperature, derate the 16L-Ceramic DIP at 10 mW/§ C, and the 16L-Molded DIP at 8.3 mW/§ C.
Note 3: Selected devices with tightened tolerance reference voltage available.
Note 4: These limits apply when the voltage measured at Lead 3 is within the range specified.
3
Functional Description
The basic oscillator (switching) frequency is controlled by an
external resistor (RT) and capacitor (CT). The relationship
between the values of RT, CT and frequency is shown in
Figure 10 .
The level of the sawtooth wave form is compared with an
error voltage by the pulse width modulated comparator. The
output of the PWM Comparator directs the pulse steering
flip-flop and the output control logic.
The error voltage is generated by the error amplifier. The
error amplifier boosts the voltage difference between the
output and the 5.0V internal reference. See Figure 7 for
error amp sensing techniques. The second error amp is typically used to implement current-limiting.
The output control logic selects either push-pull or singleended operation of the output transistors (see Figure 6 ).
The dead time control prevents on-state overlap of the output transistors as can be seen in Figure 5 . The dead time is
approximately 3.0% or 5.0% of the total period if the dead
time control is grounded. This dead time can be increased
by connecting the dead time control to a voltage up to 5.0V.
The frequency response of the error amps (Figure 11) can
be modified by using external resistors and capacitors.
These components are typically connected between the
compensation terminal and the inverting input of the error
amps.
The switching frequency of two or more LM494 circuits can
be synchronized. The timing capacitor, CT, is connected as
shown in Figure 8 . Charging current is provided by the master circuit. Discharging is through all the circuits slaved to
the master. RT is required only for the master circuit.
TL/H/10056 – 5
TL/H/10056 – 6
FIGURE 3. Common Emitter Configuration
Test Circuit and Waveform
TL/H/10056 – 7
Test Circuits
TL/H/10056 – 8
FIGURE 4. Emitter Follower Configuration
Test Circuit and Waveform
TL/H/10056–3
FIGURE 1. Error Amplifier Test Circuit
TL/H/10056–4
FIGURE 2. Current Limit Sense
Amplifier Test Circuit
TL/H/10056 – 9
FIGURE 5. Dead Time and Feedback
Control Test Circuit
4
Typical Applications
TL/H/10056 – 10
TL/H/10056 – 11
FIGURE 6. Output Connections for Single Ended
and Push-Pull Configurations
TL/H/10056 – 12
TL/H/10056 – 13
FIGURE 7. Error Amplifier Sensing Techniques
TL/H/10056 – 14
FIGURE 8. Slaving Two or More Control Circuits
5
Typical Applications (Continued)
TL/H/10056 – 15
FIGURE 9. Error Amplifier and Current Limit
Sense Amplifier Output Circuits
Typical Performance Characteristics
TL/H/10056–16
TL/H/10056 – 17
FIGURE 10. Oscillator Frequency
vs Timing Resistance
FIGURE 11. Amplifier Voltage Gain vs Frequency
6
Voltage Waveforms
TL/H/10056 – 18
Physical Dimensions inches (millimeters)
16-Lead Ceramic Dual-In-Line Package (J)
Order Number LM494CJ
NS Package Number J16A
7
LM494 Pulse Width Modulated Control Circuit
Physical Dimensions inches (millimeters) (Continued)
16-Lead Molded Dual-In-Line Package (N)
Order Number LM494CN or LM494IN
NS Package Number N16A
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