Datasheet LM494IN, LM494CN, LM494CJ Datasheet (NSC)

TL/H/10056

LM494 Pulse Width Modulated Control Circuit

June 1989

LM494
Pulse Width Modulated Control Circuit

General Description

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

§

Cto70§C and

for the LM494V is

b

40§Ctoa85§C.

Features

Y

Uncommitted output transistors capable of 200 mA
source or sink

Y

On-chip error amplifiers

Y

On-chip 5.0V reference

Y

Internal protection from double pulsing of outputs with
narrow pulse widths or with supply voltages below
specified limits

Y

Dead time control comparator

Y

Output control selects single ended or push-pull opera­tion

Y

Easily synchronized (slaved) to other circuits

Block Diagram

TL/H/10056– 2

Connection Diagram

16-Lead DIP

TL/H/10056– 1

Top View

Ordering Information

Device Package Package

Code Code Description

LM494IN N16A Molded DIP
LM494CJ J16A Ceramic DIP
LM494CN N16A Molded DIP

C

1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.

Absolute Maximum Ratings

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.

Storage Temperature Range

Ceramic DIP

b

65§Ctoa175§C

Molded DIP

b

65§Ctoa150§C

Operating Temperature Range

Industrial (LM494I)

b

40§Ctoa85§C

Commercial (LM494C) 0

§

Ctoa70§C

Lead Temperature

Ceramic DIP (Soldering, 60 sec.) 300

§

C

Molded DIP (Soldering, 10 sec.) 265

§

C

Internal Power Dissipation (Notes 1, 2)

16L-Ceramic DIP 1.50W
16L-Molded DIP 1.04W

Supply Voltage 42V

Voltage from Any Lead to Ground

(except Lead 8 and Lead 11) V

CC

a

0.3V

Output Collector Voltage 42V

Peak Collector Current

(I

C1

and IC2) 250 mA

ESD Susceptibility (to be determined)

Recommended Operating
Conditions

Power Supply Voltage (VCC) 7.0V to 40V

Voltage on Any Lead

except Leads 8 and 11
(Referenced to Ground) (V

I

)

b

0.3V to V

CC

a

0.3V

Output Voltage Collector (V

C1,VC2

)

b

0.3V to 40V

Output Collector Current (IC1,IC2) 200 mA

Timing Capacitor (CT) 470 pF to 10 mF

Timing Resistor (RT) 1.8 kX to 500 kX

Oscillator Frequency (f

OSC

) 1.0 kHz to 300 kHz

LM494
Electrical Characteristics

T

A

e

0§Ctoa70§C for the LM494C, T

A

eb

40§Ctoa85§C for the LM494I, V

CC

e

15V, f

OSC

e

10 kHz, unless otherwise specified

Symbol Parameter Conditions Min Typ Max Units

REFERENCE SECTION

V

REF

Reference Voltage (Note 3) I

REF

e

1.0 mA 4.75 5.0 5.25 V

Reg

LINE

Line Regulation of 7.0VsV

CC

s

40V

2.0 25 mV

Reference Voltage

TCV

REF

Temperature Coefficient of 0§CsT

A

s

70§C

0.01 0.03 %/

§

C

Reference Voltage

Reg

LOAD

Load Regulation of 1.0 mAsI

REF

s

10 mA

1.0 15 mV

Reference Voltage

I

OS

Output Short Circuit Current V

REF

e

0V 0§CsT

A

s

a

70§C103550

mA

b

40§CsT

A

s

a

85§C35

OSCILLATOR SECTION

f

OSC

Oscillator Frequency C

T

e

0.01 mF,
10 kHz

(Figure 10)

R

T

e

12 kX

Df

OSC

Oscillator Frequency Change C

T

e

0.01 mF, 0§CsT

A

s

a

70§C 2.0

%

R

T

e

12 kX

b

40§CsT

A

s

a

85§C 2.0

DEAD TIME CONTROL SECTION

I

IB (DT)

Input Bias Current V

CC

e

15V, 0VsV

4

s

5.25V

b

2.0b10 mA

DC

(Max)

Maximum Duty Cycle, V

CC

e

15V, Lead 4e0V,

45 %

Each Output Output Control

e

V

REF

V

TH(in)

Input Threshold Voltage Zero Duty Cycle 3.0 3.3

V

Maximum Duty Cycle 0

ERROR AMPLIFIER SECTIONS

V

IO

Input Offset Voltage V

3

e

2.5VV

3

e

2.5V 2.0 10 mV

I

IO

Input Offset Current V

3

e

2.5V 25 250 nA

I

IB

Input Bias Current V

3

e

2.5V 0.2 1.0 mA

V

ICR

Input Common Mode 7.0VsV

CC

s

40V

b

0.3 V

CC

V

Voltage Range

A

VS

Large Signal Voltage Gain 0.5VsV

3

s

3.5V 60 74 dB

BW Bandwidth 650 kHz

2

LM494
Electrical Characteristics

T

A

e

0§Ctoa70§C for the LM494C, T

A

eb

40§Ctoa85§C for the LM494I,

V

CC

e

15V, f

OSC

e

10 kHz, unless otherwise specified (Continued)

Symbol Parameter Conditions Min Typ Max Units

PWM COMPARATOR SECTION

(Figure 9)

V

THI

Inhibit Threshold Voltage Zero Duty Cycle 4.0 4.5 V

I

O

b

Output Sink Current 0.5VsV

3

s

3.5V

b

0.2b0.6 mA

(Note 4)

I

O

a

Output Source Current 0.5VsV

3

s

3.5V

2.0 mA

(Note 4)

OUTPUT SECTION

V

CE(sat)

Output Saturation V

E

e

0V, 0§CsT

A

s

a

70§C

Voltage Common Emitter I

C

e

200 mA

b

40§CsT

A

s

a

85§C 1.1 1.3

Configuration

(Figure 3)

V

Emitter Follower V

C

e

15V, I

E

e

200 mA

1.5 2.5

Configuration

(Figure 4)

I

C(off)

Collector Off-State Current V

CC

e

40V, V

CE

e

40V 2.0 100 mA

I

E(off)

Emitter Off-State Current V

CC

e

V

C

e

40V, 0§CsT

A

s

a

70§C,

b

100 mA

V

E

e

0

b

40§CsT

A

s

a

85§C

OUTPUT CONTROL

(Figure 6)

V

OCL

Output Control Voltage
Required for Single Ended or 0.4 V
Parallel Output Operation

V

OCH

Output Control Voltage
Required for Push-Pull 2.4 V
Operation

TOTAL DEVICE

I

CC

Standby Power Supply Current 6.0 10 mA

OUTPUT AC CHARACTERISTICS Use Recommended Operating Conditions with T

A

e

25§C

t

r

Rise Time of Output Voltage
Common Emitter Configuration 100 200

(Figure 3)

ns

Emitter Follower Configuration

100 200

(Figure 4)

t

f

Fall Time of Output Voltage
Common Emitter Configuration 25 100

(Figure 3)

ns

Emitter Follower Configuration

40 100

(Figure 4)

Note 1: T

J 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 (R

T

) and capacitor (CT). The relationship

between the values of R

T,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, C

T

, 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. R

T

is required only for the master circuit.

Test Circuits

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– 5

TL/H/10056– 6

FIGURE 3. Common Emitter Configuration

Test Circuit and Waveform

TL/H/10056– 7

TL/H/10056– 8

FIGURE 4. Emitter Follower Configuration

Test Circuit and Waveform

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

FIGURE 10. Oscillator Frequency

vs Timing Resistance

TL/H/10056– 17

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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with instructions for use provided in the labeling, can effectiveness.
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