ALLEGRO ULN3718

3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
Data Sheet
27117.25
3718
LOW-VOLTAGE
AUDIO POWER AMPLIFIER
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.
T
C
U Y
D L
O
N
R
O
P E
D
C
E
N
U
E
N ER
I
T
N EF
O
R
C R
S
I
O
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 operation 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 enhanced power dissipation ratings.
FEATURES
■
■
■
■
■
■
■
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
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC . . . . . . . . . . . . . . 10 V
Package Power Dissipation,
PD . . . . . . . . . . . . . . . . . . . . See Graph
Operating Temperature Range,
TA . . . . . . . . . . . . . . . .
-20°C to +85°C
Storage Temperature Range,
TS . . . . . . . . . . . . . . .
-65°C to +150°C
Always order by complete part number: ULN3718M .
3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = 3 V, RL = 32Ω, fin = 400 Hz
(unless otherwise noted).
Characteristic
Symbol
Supply Voltage Range
VCC
Quiescent Supply Current
ICC
Voltage Gain
Test Conditions
Min.
POUT
Distortion
THD
Units
1.8
3.0
9.0
V
VCC = 3.0 V
—
6.0
10
mA
VCC = 6.0 V
—
9.0
15
mA
VCC = 9.0 V
—
12
20
mA
36
40
44
dB
RL = 8Ω, VCC = 3.0 V, THD = 10%
—
80
—
mW
RL = 8Ω, VCC = 6.0 V, THD = 10%
250
430
—
mW
RL = 32Ω, VCC = 3.0 V, THD = 10%
15
25
—
mW
RL = 32Ω, VCC = 6.0 V, THD = 10%
—
125
—
mW
POUT = 10 mW
—
0.3
1.0
%
POUT = 1.0 mW, VCC = 1.8 V
—
1.5
3.0
%
AV
Audio Power Output
Limits
Typ.
Max.
Output Noise
Vout
Input Shorted, BW = 80 kHz
—
200
500
µV
Input Resistance
RIN
Pin 8
—
250
—
kΩ
CD (Pin 1) = 500 µF, f = 120 Hz
—
28
—
dB
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
Power Supply Rejection
PSRR
TEST CIRCUIT AND TYPICAL
APPLICATION
2.0
RθJC = 55°C/W
1.5
1.0
0.5
0
25
FREE AIR, R θJA = 80°C/W
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
OUTPUT POWER AS A
FUNCTION OF SUPPLY VOLTAGE
1000
5
8Ω
L =
L =
16
Ω
600
R
10
THD = 10%
f in = 400 Hz
800
R
OUTPUT POWER, POUT IN mW
15
400
2Ω
=3
RL
200
0
0
0
2
4
6
8
SUPPLY VOLTAGE, VCC IN VOLTS
0
10
2
4
6
8
SUPPLY VOLTAGE, VCC IN VOLTS
Dwg. GS-011
10
Dwg. GS-010
POWER SUPPLY REJECTION RATIO
AS A FUNCTION OF FREQUENCY
0
POWER SUPPLY REJECTION RATIO IN dB
QUIESCENT SUPPLY CURRENT, I CC IN mA
20
10
C
D =
20
10
0
µF
C
D =
50
0
µF
30
40
10
30
100
300
FREQUENCY IN HERTZ
1k
Dwg. GS-012
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 typically 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
MAX
0.280
0.240
0.300
BSC
1
0.070
0.045
4
0.005
MIN
0.400
0.355
0.210
MAX
0.015
0.150
0.115
MIN
0.022
0.014
0.100
Dwg. MA-001-8A in
BSC
Dimensions in Millimeters
(Based on 1” = 25.4 mm)
0.355
0.204
5
8
10.92
MAX
7.11
6.10
7.62
BSC
4
1
1.77
1.15
0.13
MIN
10.16
9.02
5.33
MAX
0.39
3.81
2.93
MIN
0.558
0.356
2.54
BSC
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.
Dwg. MA-001-8A mm
3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from
the detail specifications as may be required to permit improvements in the design of its products.
Components made under military approvals will be in accordance with the approval requirements.
The information included herein is believed to be accurate and reliable. However, Allegro
MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or
other rights of third parties which may result from its use.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000