ULN3718 Allegro MicroSystems, Inc., ULN3718 Datasheet - Page 4

• Manufacturer Part Number: ULN3718
• Description: Low-voltage Audio Power Amplifier
• Manufacturer: Allegro MicroSystems, Inc.

3718
LOW-VOLTAGE AUDIO POWER AMPLIFIER
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.
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.
number of mechanisms involved. A 500 F capacitor achieves typi-
cally 25 dB rejection at 120 Hz.
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 A 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 k
values of less than 100 k
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.
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 [phone]
Selection of power-supply voltage and speaker impedance allows
External component selection for this low-power amplifier involves
Ripple rejection is not practical to calculate due to the large
The high gain and the high input impedance of the power amplifier
The selection of amplifier load impedance involves more than just
Special steps toward minimizing tendencies towards instabilities
APPLICATIONS INFORMATION
are preferred.
or less for the volume control;