Datasheet LM390N Datasheet (NSC)

LM390 1W Battery Operated Audio Power Amplifier

Y

General Description

The LM390 Power Audio Amplifier is optimized for 6V, 7.5V,
9V operation into low impedance loads. The gain is internal­ly set at 20 to keep the external part count low, but the
addition of an external resistor and capacitor between pins
2 and 6 wil increase the gain to any value up to 200. The
inputs are ground referenced while the output is automati­cally biased to one half the supply voltage.

Features

Y

Battery operation

Y

1W output power

Y

Minimum external parts

Y

Excellent supply rejection

Y

Ground referenced input

Equivalent Schematic and Connection Diagrams

Self-centering output quiescent voltage

Y

Variable voltage gain

Y

Low distortion

Y

Fourteen pin dual-in-line package

Applications

Y

AM-FM radio amplifiers

Y

Portable tape player amplifiers

Y

Intercoms

Y

TV sound systems

Y

Lamp drivers

Y

Line drivers

Y

Ultrasonic drivers

Y

Small servo drivers

Y

Power converters

Dual-In-Line Package

LM390 1W Battery Operated Audio Power Amplifier

April 1995

Order Number LM390N

TL/H/7848– 2

See NS Package Number N14A

TL/H/7848– 1

C

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

TL/H/7848

Absolute Maximum Ratings

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

Supply Voltage 10V

Package Dissipation 14-Pin DIP (Note 1) 8.3W

Input Voltage

Storage Temperature

b

65§Ctoa150§C

g

0.4V

Operating Temperature 0

Ctoa70§C

§

Junction Temperature 150§C

Lead Temperature (Soldering, 10 sec.) 260§C

Thermal Resistance

i

JC

i

JA

30§C/W
79§C/W

Electrical Characteristics T

e

25§C,

A

(Figure 1)

Symbol Parameter Conditions Min Typ Max Units

V

S

I

Q

P

OUT

A

V

BW Bandwidth V

THD Total Harmonic Distortion V

PSRR Power Supply Rejection Ratio V

Operating Supply Voltage 4 9 V

Quiescent Current V

Output Power V

Voltage Gain V

e

S

e

S

e

S

10 mF from Pin 2 to 6 46 dB

e

S

e

S

e

1 kHz, Pins 2 and 6 Open

f

e

S

Pins 2 and 6 Open, Referred to Output 50 dB

e

6V, V

6V, R

01020mA

IN

e

4X, THDe10% 0.8 1.0 W

L

6V, fe1 kHz 23 26 30 dB

6V, Pins 2 and 6 Open 300 kHz

e

6V, R

4X,P

L

6V, fe1 kHz, C

OUT

BYPASS

e

500 mW

e

0.2 1 %

10 mF,

(Note 2)

R

IN

I

BIAS

Note 1: Pins 3, 4, 5, 10, 11, 12 at 25§C. Above 25§C case, derate at 15§C/W junction to case, or 85§C/W junction to ambient.

Note 2: If load and bypass capacitor are returned to V

Input Resistance 10 50 kX

(Figure 2)

S

e

6V, Pins 7 and 8 Open 250 nA

S

, rather than ground

(Figure 1)

, PSRR is typically 30 dB.

Input Bias Current V

Typical Performance Characteristics

Maximum Device Dissipation
vs Ambient Temperature

Quiescent Supply Current vs
Supply Voltage

Power Supply Rejection Ratio
(Referred to the Output) vs
Frequency

Peak-to-Peak Output Voltage
Swing vs Supply Voltage

Voltage Gain vs Frequency Distortion vs Frequency

TL/H/7848– 5

2

Typical Performance Characteristics (Continued)

Distortion vs Output Power Output Power 4X Load

Device Dissipation vs

Application Hints

Gain Control

To make the LM390 a more versatile amplifier, two pins (2
and 6) are provided for gain control. With pins 2 and 6 open,
the 1.35 kX resistor sets the gain at 20 (26 dB). If a capaci­tor is put from pin 2 to 6, bypassing the 1.35 kX resistor, the
gain will go up to 200 (46 dB). If a resistor is placed in series
with the capacitor, the gain can be set to any value from 20
to 200. A low frequency pole in the gain response is caused
by the capacitor working against the external resistor in se­ries with the 150X internal resistor. If the capacitor is elimi­nated and a resistor connects pin 2 to 6 then the output dc
level may shift due to the additional dc gain. Gain control
can also be done by capacitively coupling a resistor (or
FET) from pin 6 to ground, as in

Additional external components can be placed in parallel
with the internal feedback resistors to tailor the gain and
frequency response for individual applications. For example,
we can compensate poor speaker bass response by fre­quency shaping the feedback path. This is done with a se­ries RC from pin 6 to 13 (paralleling the internal 15 k X resis­tor). For 6 dB effective bass boost: Rj15 kX, the lowest
value for good stable operation is R
open. If pins 2 and 6 are bypassed then R as low as 2 kX
can be used. This restriction is because the amplifier is only
compensated for closed-loop gains greater than 9 V/V.

Input Biasing

The schematic shows that both inputs are biased to ground
witha50kXresistor. The base current of the input transis-
tors is about 250 nA, so the inputs are at about 12.5 mV
when left open. If the dc source resistance driving the
LM390 is higher than 250 kX it will contribute very little
additional offset (about 2.5 mV at the input, 50 mV at the
output). If the dc source resistance is less than 10 kX, then
shorting the unused input to ground will keep the offset low
(about 2.5 mV at the input 50 mV at the output). For dc
source resistances between these values we can eliminate
excess offset by putting a resistor from the unused input to
ground, equal in value to the dc source resistance. Of
course all offset problems are eliminated if the input is ca­pacitively coupled.

When using the LM390 with higher gains (bypassing the

1.35 kX resistor between pins 2 and 6) it is necessary to

Figure 7

.

e

10 kX if pin 2 is

Device Dissipation vs
Output Power 8X Load

TL/H/7848– 6

bypass the unused input, preventing degradation of gain
and possible instabilities. This is done with a 0.1 mF capaci­tor or a short to ground depending on the dc source resist­ance on the driven input.

Bootstrapping

The base of the output transistor of the LM390 is brought
out to pin 9 for Bootstrapping. The output stage of the am­plifier during positive swing is shown in
external circuitry.

a

R1

R2 set the amount of base current available to the
output transistor. The maximum output current divided by
beta is the value required for the current in R1 and R2:

e

0

j

B

(VS/2)bV

O

e

BE

2P

O

R

L

(6/2)b0.7

0.632

#

4C

c

b

O

L

a

(R1

R2)eb

Good design values are V

Example 0.8 watt into 4X load with V

I

O MAX

a

R2)e100

(R1

To keep the current in R2 constant during positive swing
capacitor C
R1 and R2 above the supply, maintaining a constant voltage
across R2. To minimize the value of C
due to C
due to the output coupling capacitor and the load. This
gives:

Example: for 100 Hz pole and R
C

B

the same current, C
4, as in

For reduced component count the load can replace R1. The
value of (R1
is both the coupling and the bootstrapping capacitor (see

Figure 2

is added. As the output swings positive CBlifts

B

and R1 and R2 is usually set equal to the pole

B

C

e

16 mF, if R1 is made a diode and R2 increased to give

Figure 4

).

can be decreased by about a factor of

B

.

a

R2) is the same, so R2 is increased. Now C

Figure 3

BE

I

O MAX

0.7V and b

e

j

e

O

e

6V.

S

632 mA

e

J

,R1eR2. The pole

B

C

c

25

4X;C

c

e

100.

364X

e

400 mF and

with its

B

3

Typical Applications

FIGURE 1. Load Returned to Ground

(Amplifier with Gain

e

20)

FIGURE 3

TL/H/7848– 3

TL/H/7848– 7

FIGURE 2. Load Returned to Supply

(Amplifier with Gain

e

TL/H/7848– 4

20)

TL/H/7848– 8

FIGURE 4. Amplifier with Gaine200 and Minimum C

B

FIGURE 5. 2.5W Bridge Amplifier

4

TL/H/7848– 9

Typical Applications (Continued)

FIGURE 6(a). Amplifier with Bass Boost

FIGURE 7. Intercom

TL/H/7848– 10

FIGURE 6(b). Frequency Response

TL/H/7848– 11

with Bass Boost

TL/H/7848– 12

FIGURE 8. AM Radio Power Amplifier

Note 1: Twist supply lead and supply ground very tightly.

Note 2: Twist speaker lead and ground very tightly.

Note 3: Ferrite bead is Ferroxcube K5-001-001/3B with 3 turns of wire.

TL/H/7848– 13

Note 4: R1C1 band limits input signals.

Note 5: All components must be spaced very close to IC.

5

Physical Dimensions inches (millimeters)

Molded Dual-In-Line Package (N)

Order Number LM390N

See NS Package Number N14A

LM390 1W Battery Operated Audio Power Amplifier

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