Texas Instruments TPA721 User manual

2001 Mixed-Signal Products
TPA721 MSOP
Audio Power Amplifier
Evaluation Module
User’s Guide
SLOU033A

IMPORTANT NOTICE
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Customers are responsible for their applications using TI components.
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Mailing Address:
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Copyright 2001, Texas Instruments Incorporated

iii
Chapter Title—Attribute Reference
Preface
Related Documentation From Texas Instruments
J TI Plug-N-Play Audio Amplifier Evaluation Platform (literature
number SLOU011) provides detailed information on the evaluation
platform and its use with TI audio evaluation modules.
J TPA721 700-mW Low-Voltage Audio Power Amplifier (literature
number SLOS231) This is the data sheet for the TPA721 audio
amplifier integrated circuit.
FCC Warning
This equipment is intended for use in a laboratory test environment only. It
generates, uses, and can radiate radio frequency energy and has not been
testedfor compliance with thelimitsof computing devices pursuanttosubpart
Jofpart 15of FCCrules, whicharedesignedtoprovidereasonableprotection
against radio frequency interference. Operation of this equipment in other
environments may cause interference with radio communications, in which
case the user at his own expense will be required to take whatever measures
may be required to correct this interference.
Trademarks
TI is a trademark of Texas Instruments Incorporated.

iv

Running Title—Attribute Reference
v
Chapter Title—Attribute Reference
Contents
1 Introduction 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Feature Highlights 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Description 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 TPA721 EVM Specifications 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Quick Start 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Precautions 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Quick Start List for Platform 2-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Quick Start List for Stand-Alone 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Details 3-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Precautions 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 The TPA721 MSOP Audio Amplifier Evaluation Module 3-3. . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1 TPA721 Audio Amplifier IC 3-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.2 BTL Operation 3-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.3 Module Gain 3-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.4 Shutdown 3-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.5 Internal Depop Circuitry 3-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Using The TPA721 MSOP EVM With The Plug-N-Play Evaluation Platform 3-6. . . . . . . . .
3.3.1 Installing and Removing EVM Boards 3-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.2 Signal Routing 3-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3 Mute/Mode 3-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.4 Power Requirements 3-9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.5 Inputs and Outputs 3-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Using The TPA721 MSOP EVM Stand-ALone 3-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1 TPA721 MSOP EVM Connected for BTL Output 3-11. . . . . . . . . . . . . . . . . . . . . . . .
3.5 TPA721 MSOP Audio Amplifier Evaluation Module Parts List 3-12. . . . . . . . . . . . . . . . . . . .

Running Title—Attribute Reference
vi
Figures
1–1 The TI TPA721 MSOP Audio Amplifier Evaluation Module 1-3. . . . . . . . . . . . . . . . . . . . . . . . . .
2–1 Quick Start Platform Map 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–2 Quick Start Module Map 2-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–1 The TI Plug-N-Play Audio Amplifier Evaluation Platform 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–2 TPA721 MSOP EVM 3-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–3 TPA721 MSOP EVM Schematic Diagram 3-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–4 TPA721 Audio Amplifier IC 3-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–5 Platform Signal Routing and Outputs 3-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–6 Mute/Mode and Polarity Control 3-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–7 Typical Headphone Plug 3-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–8 TPA721 MSOP EVM Connected for Stereo BTL Output 3-11. . . . . . . . . . . . . . . . . . . . . . . . . . .
Tables
2–1 Typical TI Plug-N-Play Platform Jumper and Switch Settings for the
TPA721 MSOP EVM 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–2 Platform Jumper and Switch Settings for the TPA721 MSOP EVM 2-3. . . . . . . . . . . . . . . . . . .
3–1 TPA721 MSOP EVM Parts List 3-12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1
Introduction
Introduction
This chapter provides an overview of the Texas Instruments (TI) TPA721
MSOPaudio amplifierevaluationmodule(SLOP215). It includes alistofEVM
features, a brief description of the module illustrated with a pictorial diagram,
and a list of EVM specifications.
Topic Page
1.1 Feature Highlights 1–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Description 1–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.3 TPA721 MSOP EVM Specifications 1–3. . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1

Feature Highlights
1-2 Introduction
1.1 Feature Highlights
The TI TPA721 MSOP audio amplifier evaluation module and the TI
plug-n-play audio amplifier evaluation platform include the following features:
- TPA721 Low-Voltage Audio Power Amplifier Evaluation Module
J Single channel, bridge-tied load (BTL)
J 3.3-V and 5-V operation
J 700-mW output power into 8 Ωat 5 V, BTL
J Internal depop circuitry
J Internal thermal and short-circuit protection
J Module gain is set at –4 V/V in BTL mode, –2 V/V in SE mode
- Quick and Easy Configuration With the TI Plug-N-Play Audio Amplifier
Evaluation Platform
J Evaluation module is designed to simply plug into the platform,
automatically making all signal, control, and power connections
J Platform provides flexible power options
J Jumpers on the platform select power and module control options
J Switches on the platform route signals
J Platformprovides quick and easy audio inputand output connections
- Platform Power Options
J Onboard 9-V battery
J External 5-V –15-V (VCC) supply inputs
J External regulated VDD supply input
J Socket for onboard 5-V/3.3-V VDD voltage regulator EVM
J Onboard overvoltage and reverse polarity power protection
- Platform Audio Input and Output Connections
J Left and right RCA phono jack inputs
J Miniature stereo phone jack input
J Left and right RCA phono jack outputs
J Left and right compression speaker terminal outputs
J Miniature stereo headphone jack output

Description
1-3
Introduction
1.2 Description
The TPA721 MSOP audio power amplifier evaluation module is a complete,
low-power single-channel audio power amplifier. It consists of the TI TPA721
700-mWlow-voltage audiopower amplifierICin averysmall MSOPpackage,
along with a small number of other parts mounted on a circuit board that is
approximately one and a quarter inches square (Figure 1–1).
Figure 1–1.The TI TPA721 Audio Amplifier Evaluation Module
OUT+
IN–
GND
Vdd GND
U1 †
Shutdown
R5
OUT–
GND
C4
TEXAS
INSTRUMENTS
SLOP215
TPA721 MSOP EVM
C6
C5
S1 R1
+
R2
C2
C1
R3
R4
C3
†Due to the very small size of the MSOP IC package, the standard part number TPA721 is replaced with the code TIABC.
Single in-line header pins are mounted to the underside of the module circuit
board to allow the EVM to be plugged into the TI plug-n-play audio amplifier
evaluation platform or to be wired directly into existing circuits and equipment
when used stand-alone.
The platform, with room for a pair of TPA721 MSOP evaluation modules, is a
convenient vehicle for demonstrating TI’s audio power amplifier and related
evaluation modules. The EVMs simply plug into the platform, which
automatically provides power to the modules, interconnects them correctly,
andconnectsthemtoaversatilearrayofstandardaudioinputandoutputjacks
and connectors. Easy-to-use configuration controls allow the platform and
EVMs to quickly model many possible end-equipment configurations.
There is nothing to build, nothing to solder, and nothing but the speakers
included with the platform to hook up.
1.3 TPA721 EVM Specifications
Supply voltage range, VDD 2.5 V to 5.5 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Supply current, IDD 450 mA, max. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Continuous output power, PO:8-ΩBTL, VDD = 5 V 700 mW. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Audio input voltage, VI2 Vpp, max. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum load impedance, RL8 Ω. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-4 Introduction

2-1
Quick Start
Quick Start
Follow the steps in this chapter to quickly prepare the TPA721 MSOP audio
amplifier EVM for use. Using the TPA721 MSOP EVM with the TI plug-n-play
audio amplifier evaluation platform is a quick and easy way to connect power,
signal and control inputs, and signal outputs to the EVM, using standard
connectors. However, the audio amplifier evaluation module can be used
stand-alone by making connections directly to the module pins, and can be
wired directly into existing circuits or equipment.
Theplatform switch and jumper settings shown in Table2–1 are typical for the
TPA721 MSOP EVM. They will cause the TPA721 amplifier IC on the EVM to
shut down when a plug is inserted into platform headphone jack J10.
Table 2–1. Typical TI Plug-N-Play Platform Jumper and Switch Settings for the TPA721
MSOP EVM
EVM JP6 JP7 JP8 S2 S3
TPA721 Mute X Hi Note 2 X
Notes: 1) X = Don’t care
2) SetS2 to ON when signalconditioning boardis installedin U1; set S2
to OFF when no signal conditioning board is installed.
Topic Page
2.1 Precautions 2–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Quick Start List for Platform 2–3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Quick Start List for Stand-Alone 2–4. . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 2

Precautions
2-2 Quick Start
2.1 Precautions
Power Supply Input Polarity and Maximum Voltage
Always ensure that the polarity and voltage of the external power
connected to VCC power input connector J1, J2, and/or VDD power
input connector J6 are correct. Overvoltage or reverse-polarity
power applied to these terminals can open onboard soldered-in
fuses and cause other damage to the platform, installed evaluation
modules, and/or the power source.
Inserting or Removing EVM Boards
Do not insert or remove EVM boards with power applied –damage
to the EVM board, the platform, or both may result.
Figure 2–1.Quick Start Platform Map
Signal Conditioning
****CAUTION****
Do not insert or remove
EVM boards with power
applied
ICC
JP4
F1
VR1
R1
JP3
JP2 JP1 AC/DC
(J2)
VCC(J1)
D1 D2 D3
D4 J2
J3 J4 J5
AC/DC
In
VCC
In
+
J1
DC
SOURCE
LED1 VCC
LED2 VDD
R2
JP5 IDD
B1
U6
POWER
SUPPLY
U3 U4
U5
U1
U2
Audio
Power
Amps
OnOff ConditioningS2
J7 J8 Right
Out Left
Out
+–+–
JP6
Mode
Mute
Spk(U2-U4)
JP8
J9 Left
Out
JP7
S3 HP Source
U2-U4
U5
Polarity
Lo
Hi
HP(U5)
C3 C2
++
R3
R5
J10
Stereo
HP Out
TP1
GND
Plug-N-PlayAudio Amplifier
Evaluation Platform
SLOP097 Rev. C.1
Stereo
In
Right
In Left
In
J6 In/Out VDD
F2
VR2 +
DC
Power
In/Out
Speaker
Output
Headphone
Output
Audio
Input
Power
Input
Batt
C1+
Right
Out
On Off Pwr
S1
TEXAS INSTRUMENTS 1997
R4
6a
1
3
6b
6b
6b 6b
89
10
9
2
4
5

Quick Start List for Platform
2-3
Quick Start
2.2 Quick Start List for Platform
FollowthesestepswhenusingtheTPA721MSOPEVMwiththeTIplug-n-play
audio amplifier evaluation platform (see the platform user’s guide, SLOU011,
for additional details). Numbered callouts for selected steps are shown in
Figure 2–1 and details appear in Chapter 3.
- Platform preparations
1) EnsurethatallexternalpowersourcesaresettoOFFandthattheplatform
power switch S1 is set to OFF.
2) Install a TPA721 MSOP module in platform sockets U3 and U4 for stereo
operation (or a module in either U3 or U4 for single channel operation),
taking care to align the module pins correctly.
3) Use switch S2 to select or bypass the signal conditioning EVM (U1).
4) Set control signal Polarity jumper JP8 to Hi.
5) Set jumper JP6 to select the Mute control input (causes the TPA721 to
shut down if a plug is inserted into platform headphone jack J10).
Table 2–2. Platform Jumper and Switch Settings for the TPA721 MSOP EVM
EVM JP6 JP7 JP8 S2 S3
TPA721 Mute X Hi Note 2 X
Notes: 1) X = Don’t care
2) SetS2 to ON whensignal conditioning boardis installed inU1; set S2
to OFF when no signal conditioning board is installed.
- Power supply
6) Select and connect the power supply:
a) Connectan external regulated powersupplyset to a voltagebetween
2.5Vand5.5VtoplatformVDD powerinputconnectorJ6, takingcare
to observe marked polarity,
or
b) InstallavoltageregulatorEVM(SLVP097orequiv.)inplatformsocket
U6. Install a 9-V battery in B1 or connect a 7 V –12 V power source
to a platform VCC power input J1 or J2 and jumper the appropriate
power input (see platform user’s guide).
- Inputs and outputs
7) Ensure that signal source level is set to minimum.
8) Connect the audio source to left and right RCA phono jacks J3 and J5 or
stereo miniature phone jack J4.
9) Connect 8-Ω–32-Ωspeakers to left and right RCA jacks J7 and J9 or to
stripped wire connectors J8.
- Power Up
10) Verifycorrect voltage and input polarity andset the external powersupply
to ON. If VCC and an on-board regulator EVM are used to provide VDD,
set platform power switch S1 to ON.
PlatformLED2shouldlightindicatingthepresenceofVDD,andtheevaluation
modules installed on the platform should begin operation.
11) Adjust the signal source level as needed.

Quick Start List for Stand-Alone
2-4 Quick Start
2.3 Quick Start List for Stand-Alone
Follow these steps to use the TPA721 MSOP EVM stand-alone or when
connecting it into existing circuits or equipment. Connections to the TPA721
MSOP module header pins can be made via individual sockets,
wire-wrapping, or soldering to the pins, either on the top or the bottom of the
module circuit board. Numbered callouts for selected steps are shown in
Figure 2–2 and details appear in Chapter 3.
Figure 2–2.Quick Start Module Map
5
2
6
4
OUT+
IN–
IN+
Vdd GND
U1 †
Shutdown
R5
OUT–
GND
C4
TEXAS
INSTRUMENTS
SLOP215
TPA721 MSOP EVM
C6
C5
S1 R1
+
R2
C2
C1
R3
R4
C3
†Due to the very small size of the MSOP IC package, the standard part number TPA721 is replaced with the code TIABC
- Power supply
1) Ensure that all external power sources are set to OFF.
2) Connectan external regulated power supplyset to5 V tothe module Vdd
and GND pins, taking care to observe marked polarity.
- Inputs and outputs
3) Ensure that the signal source level is set to minimum.
4) ConnectthepositiveleadfromtheaudiosourcetothemoduleIN–pinand
the negative lead to the In+ pin.
5) Connect the S1 pin to VDD through a normally open switch.
6) Connect an 8-Ω–32-Ωspeaker to the module OUT+ and OUT–pins.
- Power Up
7) Verifycorrect voltage and input polarity andset the external powersupply
to ON.
The EVM should begin operation.
8) Adjust the signal source level as needed.

3-1
Details
Details
This chapter provides details on the TPA721 IC, the evaluation module, the
stepsin theQuick-Start List,additionalapplication information,anda partslist
for the TPA721 MSOP evaluation module.
Topic Page
3.1 Precautions 3–2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 The TPA721 MSOP Audio Power Amplifier Evaluation Module 3–3. .
3.3 Using The TPA721 MSOP EVM With The Plug-N-Play
Evaluation Platform 3–6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Using The TPA721 MSOP EVM Stand-Alone 3–11. . . . . . . . . . . . . . . . . . . .
3.5 TPA721 MSOP Audio Power Amplifier Evaluation
Module Parts List 3–12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 3

Precautions
3-2 Details
3.1 Precautions
Power Supply Input Polarity and Maximum Voltage
Always ensure that the polarity and voltage of the external power
connected to VCC power input connector J1, J2, and/or VDD power
input connector J6 are correct. Overvoltage or reverse-polarity
power applied to these terminals can open onboard soldered-in
fuses and cause other damage to the platform, installed evaluation
modules, and/or the power source.
Inserting or Removing EVM Boards
Do not insert or remove EVM boards with power applied –damage
to the EVM board, the platform, or both may result.
Figure 3–1.The TI Plug-N-Play Audio Amplifier Evaluation Platform
Signal Conditioning
****CAUTION****
Do not insert or remove
EVM boards with power
applied
ICC
JP4
F1
VR1
R1
JP3
JP2 JP1 AC/DC
(J2)
VCC(J1)
D1 D2 D3
D4 J2
J3 J4 J5
AC/DC
In
VCC
In
+
J1
DC
SOURCE
LED1 VCC
LED2 VDD
R2
JP5 IDD
B1
U6
POWER
SUPPLY
U3 U4
U5
U1
U2
Audio
Power
Amps
OnOff ConditioningS2
J7 J8 Right
Out Left
Out
+–+–
JP6
Mode
Mute
Spk(U2-U4)
JP8
J9 Left
Out
JP7
S3 HP Source
U2-U4
U5
Polarity
Lo
Hi
HP(U5)
C3 C2
++
R3
R5
J10
Stereo
HP Out
TP1
GND
Plug-N-PlayAudio Amplifier
Evaluation Platform
SLOP097 Rev. C.1
Stereo
In
Right
In Left
In
J6 In/Out VDD
F2
VR2 +
DC
Power
In/Out
Speaker
Output
Headphone
Output
Audio
Input
Power
Input
Batt
C1+
Right
Out
On Off Pwr
S1
TEXAS INSTRUMENTS 1997
R4

The TPA721 MSOP Audio Power Amplifier Evaluation Module
3-3
Details
3.2 The TPA721 MSOP Audio Power Amplifier Evaluation Module
The TPA721 MSOP audio power amplifier evaluation module is powered by
a TPA721 700-mW low-power audio amplifier IC. The EVM includes a
shutdown control signal input with an onboard switch for manual shutdown.
The module can be used with the TI plug-n-play audio amplifier evaluation
platform (Figure 3–1) or wired directly into circuits or equipment. The module
has single in-line header connector pins mounted to the under side of the
board. These pins allow the module to be plugged into the TI platform, which
automatically makes all the signal input and output, power, and control
connections to the module.
The module connection pins are on 0.1-inch centers to allow easy use with
standard perf board and plug board-based prototyping systems. Or, the EVM
can be wired directly into existing circuits and equipment when used
stand-alone.
The module appears in Figure 3–2 and its schematic is shown in Figure 3–3.
Figure 3–2.TPA721 MSOP EVM
OUT+
IN–
GND
Vdd GND
U1 †
Shutdown
R5
OUT–
GND
C4
TEXAS
INSTRUMENTS
SLOP215
TPA721 MSOP EVM
C6
C5
S1 R1
+
R2
C2
C1
R3
R4
C3
†Due to the very small size of the MSOP IC package, the standard part number TPA721 is replaced with the code TIABC
Figure 3–3.TPA721 MSOP EVM Schematic Diagram
C1
1 µF
C3
1 µF
R1
20 kΩ
Audio Input–
Shutdown S1
C6
5 pF
OUT–
GND
OUT+
R5
39 kΩ
R4
20 kΩ
No
C4
10 µF
C5
1 µF
Shutdown
Bypass
In+
In–
VO–
GND
VDD
VO+
8
7
6
5
1
2
3
4
GND
VDD
2.5 V to 5.5 V
+
C2
NA
GND R3
NA
R2
0 Ω
Note: NA is not assembled on PCB.

The TPA721 MSOP Audio Power Amplifier Evaluation Module
3-4 Details
3.2.1 TPA721 Audio Amplifier IC
TheTPA721audioamplifierICisaCMOSdeviceintendedforbridge-tiedload
(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
5
OUT+
4
IN –
OUT–
8
3
IN+
_
_
+
+
7
2VDD/2
VDD
GND
6
SHUTDOWN
BYPASS
1Bias Control
The IC includes two separate internal amplifiers, depop circuitry, and a
shutdown control. The two amplifiers operate as mirror images of each other
inthe bridge-tied load (BTL) configuration for increased power. BTL operation
providesmanybenefits,includingquadrupletheoutputpowerofsingle-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
otheramplifiersinthesystem.Theplatformprovidessuchisolatedoutputlines
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:
Gain +
–R5
R4
2forBTL

The TPA721 MSOP Audio Power Amplifier Evaluation Module
3-5
Details
The TPA721 amplifier IC, like most other amplifiers, exhibits its best distortion
andnoiseperformanceatlowergainlevels(seetheTPA721datasheet).Even
so, the TPA721 at its highest gain setting has significantly less distortion than
most low-cost speakers.
Gain versus total harmonic distortion (THD) should be considered in each
application.BoththemoduleinputsignallevelandtheTPA721MSOPmodule
gain should be adjusted to obtain the lowest overall distortion level for a
particularoverallgain.Aquickruleofthumb(everythingelse beingequal): the
module input signal level should be as high as possible without clipping or
overloading the TPA721 input, and the TPA721 gain should be kept as low as
possible.
3.2.4 Shutdown
When the shutdown terminal of the TPA721 amplifier IC is taken high, the IC
ceases operation and enters a low-power state. This is accomplished by
applying a control signal to the module shutdown pin (S1) or by pressing the
shutdown switch on the module. When the control signal goes low or is
removed (or the switch is released), amplifier operation resumes.
The plug-n-play platform can generate the shutdown (mute) signal for the
moduleeither when a plug is insertedintotheplatformheadphone output jack
or when the plug is removed, as selected by a platform jumper (JP8).
3.2.5 Internal Depop Circuitry
Internal depop circuitry reduces or eliminates the various turn-on transients
thatmightappearattheoutputduringthetransitionfrompowerofforshutdown
mode to normal operation. These output transients are often heard as a pop
from the speaker and occur when the two amplifiers in the IC turn on or off at
differentrates,causingavoltagespiketoappearacrosstheoutput.Thedepop
circuitryaddsadelaywith anRC networkat theamplifier ICbypass pintohelp
ensurethat theamplifiersturn onandoffatthe same rate,thuseliminating the
pop. For best results, bypass capacitor C1 should have a value between
0.1 µF and 2.2 µF. A 1 µF unit was selected for the EVM.

Using The TPA721 MSOP EVM With the Plug-N-Play Evaluation Platform
3-6 Details
3.3 Using The TPA721 MSOP EVM With the Plug-N-Play Evaluation Platform
The TPA721 MSOP audio amplifier evaluation module was designed to be
usedwiththeTIplug-n-playaudioamplifierevaluationplatform.Itsimplyplugs
into socket U3 or U4.
The following paragraphs provide additional details for using the TPA721
MSOP EVM with the platform.
3.3.1 Installing and Removing EVM Boards
TI plug-n-play evaluation modules use single-in-line header pins installed on
the underside of the module circuit board to plug into sockets on the platform.
The EVM pins and the platform sockets are keyed such that only the correct
type of EVM can be installed in a particular socket, and then only with the
proper orientation.
Evaluation modules are easily removed from the platform by simply prying
them up and lifting them out of their sockets. Care must be taken, however, to
prevent bending the pins.
3.3.1.1 EVM Insertion
1) Remove all power from the evaluation platform.
2) Locate socket U3 or U4 on the platform.
3) Orient the module correctly.
4) Carefully align the pins of the module with the socket pin receptacles.
5) Gently press the module into place.
6) Check to be sure that all pins are seated properly and that none are bent
over.
3.3.1.2 EVM Removal
1) Remove all power from the evaluation platform.
2) Using an appropriate tool as a lever, gently pry up one side of the module
a small amount.
3) Changetothe oppositesideofthemoduleanduse thetooltoprythatside
up a small amount.
4) Alternate between sides, prying the module up a little more each time to
avoid bending the pins, until it comes loose from the socket.
5) Lift the EVM off the platform.