3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
3718
Data Sheet
27117.25
LOW-VOLTAGE
AUDIO POWER AMPLIFIER
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, V
CC
. . . . . . . . . . . . . .
10 V
Package Power Dissipation,
Operating Temperature Range,
T
A
. . . . . . . . . . . . . . . .
T
C
U Y
D L
O N
R O
P E
D C
E N
U E
N ER
I
T F
N E
O R
C R
S O
I
D F
—
The amplifier will operate (at reduced volume) with supply voltages
as low as 1.8 V without a significant increase in distortion. This feature
allows operation with a 3 V battery supply and minimizes concern
about weak batteries. The class-AB audio amplifier has low quiescent
current drain for maximum battery life. This device is rated for opera-
tion with supply voltages up to 9 V.
The ULN3718M audio amplifier is supplied in an 8-pin mini-DIP
plastic package. A copper alloy lead frame gives the amplifier en-
hanced power dissipation ratings.
Providing a low-cost, compact alternative to discrete transistor
amplifiers, the ULN3718M integrated circuit is ideal for application
as a headphone driver in portable radios, tape players, and other
battery-operated equipment. The low-power audio amplifier’s wide
frequency response and low noise ensure premium performance.
FEATURES
s
s
s
s
s
s
s
Wide Operating Voltage Range 1.8 - 9.0 V
Low Quiescent Current
AC Short-Circuit Protection
Low External Parts Count
Low Distortion
40 dB Voltage Gain
Low Noise
P
D
. . . . . . . . . . . . . . . . . . . .
See Graph
-20
°
C to +85
°
C
-65
°
C to +150
°
C
Storage Temperature Range,
T
S
. . . . . . . . . . . . . . .
Always order by complete part number: ULN3718M .
3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
ELECTRICAL CHARACTERISTICS at T
A
= +25°C, V
CC
= 3 V, R
L
= 32Ω, f
in
= 400 Hz
(unless otherwise noted).
Characteristic
Supply Voltage Range
Quiescent Supply Current
Symbol
V
CC
I
CC
V
CC
= 3.0 V
V
CC
= 6.0 V
V
CC
= 9.0 V
Voltage Gain
Audio Power Output
A
V
P
OUT
R
L
= 8Ω, V
CC
= 3.0 V, THD = 10%
R
L
= 8Ω, V
CC
= 6.0 V, THD = 10%
R
L
= 32Ω, V
CC
= 3.0 V, THD = 10%
R
L
= 32Ω, V
CC
= 6.0 V, THD = 10%
Distortion
THD
P
OUT
= 10 mW
P
OUT
= 1.0 mW, V
CC
= 1.8 V
Output Noise
Input Resistance
Power Supply Rejection
V
out
R
IN
PSRR
Input Shorted, BW = 80 kHz
Pin 8
C
D
(Pin 1) = 500
µF,
f = 120 Hz
Test Conditions
Min.
1.8
—
—
—
36
—
250
15
—
—
—
—
—
—
Limits
Typ.
Max.
3.0
6.0
9.0
12
40
80
430
25
125
0.3
1.5
200
250
28
9.0
10
15
20
44
—
—
—
—
1.0
3.0
500
—
—
Units
V
mA
mA
mA
dB
mW
mW
mW
mW
%
%
µV
kΩ
dB
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
2.0
R
θJC
= 55°C/W
TEST CIRCUIT AND TYPICAL
APPLICATION
1.5
1.0
0.5
FREE AIR, R
θJA
= 80°C/W
0
25
50
75
100
TEMPERATURE IN
°C
125
150
Dwg. GP-009-1B
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
W
Copyright © 1985, 1995, Allegro MicroSystems, Inc.
3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
TYPICAL CHARACTERISTICS
QUIESCENT SUPPLY CURRENT AS A
FUNCTION OF SUPPLY VOLTAGE
20
1000
OUTPUT POWER AS A
FUNCTION OF SUPPLY VOLTAGE
QUIESCENT SUPPLY CURRENT, I
CC
IN mA
600
L
=
R
L
=
8
Ω
15
OUTPUT POWER, P
OUT
IN mW
800
THD = 10%
f
in
= 400 Hz
10
400
2
Ω
=3
5
200
0
0
2
4
6
8
SUPPLY VOLTAGE, V
CC
IN VOLTS
10
Dwg. GS-011
0
0
2
4
6
8
SUPPLY VOLTAGE, V
CC
IN VOLTS
10
Dwg. GS-010
POWER SUPPLY REJECTION RATIO
AS A FUNCTION OF FREQUENCY
0
POWER SUPPLY REJECTION RATIO IN dB
10
C
D
=
10
0
µ
F
20
C
D
=
50
0
µ
F
30
40
10
30
100
300
FREQUENCY IN HERTZ
1k
Dwg. GS-012
R
R
L
16
Ω
3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
APPLICATIONS INFORMATION
Selection of power-supply voltage and speaker impedance allows
a designer to choose audio power levels within the allowable package
power dissipation rating for any maximum operating temperature. No
unique precautions are necessary when designing with this device. It
is stable and ac short-circuit immune.
External component selection for this low-power amplifier involves
only two capacitors — one for output coupling and one for feedback
and ripple decoupling. The coupling capacitor value should be selected
to provide the desired low-frequency cutoff with the chosen load
impedance. The decoupling capacitor should be chosen for both
low-frequency audio rolloff and supply-ripple rejection.
Ripple rejection is not practical to calculate due to the large
number of mechanisms involved. A 500
µF
capacitor achieves typi-
cally 25 dB rejection at 120 Hz.
The high gain and the high input impedance of the power amplifier
recommend use of this device in many diverse applications. However,
the input stage does have other characteristics that should be taken
into account for best results. The input is referenced to ground for
internal biasing and must be provided with a dc path to ground. A
current of typically 1
µA
flows from the input through the volume
control. This produces an IR drop that is multiplied by the closed loop
dc gain of the amplifier and appears as an error in output centering.
This recommends a value of 200 kΩ or less for the volume control;
values of less than 100 kΩ are preferred.
The selection of amplifier load impedance involves more than just
consideration of the desired power output. A low load impedance will
produce the highest power output for any given supply voltage. Higher
impedances will furnish significant reduction in harmonic distortion and
improvement in overall repeatability in power output capacity.
Special steps toward minimizing tendencies towards instabilities
of all types were taken in the design of this device. However, as with
all high-gain circuits, care should be given to printed wiring board
layout to avoid undesirable effects. Inputs and outputs should be well
separated and should avoid common-mode impedances wherever
possible. For best performance, connect low-level input-signal ground
terminals and the decoupling capacitor ground terminal together at pin
3 (signal ground); connect the high-level speaker ground terminal and
the power supply ground terminal together at pin 2 (power ground).
The signal ground and the power ground should be interconnected
at only one point.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
Dimensions in Inches
0.014
0.008
8
5
0.430
0.280
0.240
MAX
0.300
BSC
1
0.070
0.045
4
0.005
0.400
0.355
MIN
0.210
MAX
0.015
MIN
0.150
0.115
0.022
0.014
0.100
BSC
Dwg. MA-001-8A in
Dimensions in Millimeters
(Based on 1” = 25.4 mm)
0.355
0.204
8
5
10.92
7.11
6.10
MAX
7.62
BSC
1
1.77
1.15
4
0.13
10.16
9.02
MIN
5.33
MAX
0.39
MIN
3.81
2.93
0.558
0.356
2.54
BSC
Dwg. MA-001-8A mm
NOTES: 1. Lead thickness is measured at seating plane or below.
2. Lead spacing tolerance is non-cumulative.
3. Exact body and lead configuration at vendor’s option within limits shown.
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