Tpa721 Audio Amplifier Ic; Btl Operation; Module Gain; Shutdown - Texas Instruments TPA721 User Manual

The TPA721 MSOP Audio Power Amplifier Evaluation Module
3.2.1

TPA721 Audio Amplifier IC

The TPA721 audio amplifier IC is a CMOS device intended for bridge-tied load
(BTL) operation in battery-powered applications. Supplied in a very small
surface-mount package, the TPA721 has been designed to operate from low
supply voltages (between approximately 2.5 V and 5.5 V) and to deliver up to
approximately 700 mW into an 8-Ω, BTL (Figure 3 – 4). Typical applications
include portable phones, toys, games, and similar hand-held audio
applications.
Figure 3–4. TPA721 Amplifier IC
The IC includes two separate internal amplifiers, depop circuitry, and a
shutdown control. The two amplifiers operate as mirror images of each other
in the bridge-tied load (BTL) configuration for increased power. BTL operation
provides many benefits, including quadruple the output power of single-ended
operation and no need for bulky output coupling capacitors. For more
information, see the TPA721 amplifier IC data sheet, TI literature number
SLOS231.
3.2.2

BTL Operation

The TPA721 amplifier IC operates in the BTL mode, which means that the
output signal from OUT+ must go through the speaker load and be returned
directly to OUT–, and not to system ground. This requires that the OUT– line
be isolated not only from system ground, but also from the OUT– lines of any
other amplifiers in the system. The platform provides such isolated output lines
from the amplifier EVM sockets directly to separate left and right speaker
connectors.
3.2.3

Module Gain

The TPA721 MSOP evaluation module has a set gain of 2. However, the gain
can be adjusted to a maximum of 22 by changing the value of resistor R5
(Figure 3–3). Use the following equation to determine value of R4:
3-4
4
IN –
3
IN+
6
V DD
V DD /2
2
BYPASS
7
GND
1
Bias Control

SHUTDOWN

+
–R5
Gain 2 for BTL
R4
_
5
OUT+
+
_
8
OUT–
+
Details