Texas Instruments TPA6120A2 User manual


 
May 2004 HPA Audio Power
User’s Guide
SLOU169

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Mailing Address: Texas Instruments
Post Office Box 655303 Dallas, Texas 75265
Copyright 2004, Texas Instruments Incorporated

EVM IMPORTANT NOTICE
Texas Instruments (TI) provides the enclosed product(s) under the following conditions:
This evaluation kit being sold by TI is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION
PURPOSES ONLY and is not considered by TI to be fit for commercial use. As such, the goods being provided
may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective
considerations, including product safety measures typically found in the end product incorporating the goods.
As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic
compatibility and therefore may not meet the technical requirements of the directive.
Should this evaluation kit not meet the specifications indicated in the EVM User’s Guide, the kit may be returned
within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE
WARRANTY MADE BY SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED,
IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY
PARTICULAR PURPOSE.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user
indemnifies TI from all claims arising from the handling or use of the goods. Please be aware that the products
received may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). Due to the open construction
of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic
discharge.
EXCEPT TO THE EXTENT OF THE INDEMNITY SET FORTH ABOVE, NEITHER PARTY SHALL BE LIABLE
TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
TI currently deals with a variety of customers for products, and therefore our arrangement with the user is not
exclusive.
TI assumes no liability for applications assistance, customer product design, software performance, or
infringement of patents or services described herein.
Please read the EVM User’s Guide and, specifically, the EVM Warnings and Restrictions notice in the EVM
User’s Guide prior to handling the product. This notice contains important safety information about temperatures
and voltages. For further safety concerns, please contact the TI application engineer.
Persons handling the product must have electronics training and observe good laboratory practice standards.
No license is granted under any patent right or other intellectual property right of TI covering or relating to any
machine, process, or combination in which such TI products or services might be or are used.
Mailing Address:
Texas Instruments
Post Office Box 655303
Dallas, Texas 75265
Copyright 2004, Texas Instruments Incorporated

EVM WARNINGS AND RESTRICTIONS
It is important to operate this EVM within the supply voltage range of ±5 V to ±15 V.
Exceeding the specified supply range may cause unexpected operation and/or irreversible
damage to the EVM. If there are questions concerning the supply range, please contact a TI
field representative prior to connecting the input power.
Applying loads outside of the specified output range may result in unintended operation and/or
possible permanent damage to the EVM. Please consult the EVM User’s Guide prior to
connecting any load to the EVM output. If there is uncertainty as to the load specification,
please contact a TI field representative.
During normal operation, some circuit components may have case temperatures greater than
125°C. The EVM is designed to operate properly with certain components above 125°C as
long as the input and output ranges are maintained. These components include but are not
limited to linear regulators, switching transistors, pass transistors, and current sense
resistors. These types of devices can be identified using the EVM schematic located in the
EVM User’s Guide. When placing measurement probes near these devices during operation,
please be aware that these devices may be very warm to the touch.
Mailing Address:
Texas Instruments
Post Office Box 655303
Dallas, Texas 75265
Copyright 2004, Texas Instruments Incorporated

How to Use This Manual
iii
Preface

About This Manual
This users guide describes the characteristics, operation, and use of the
TPA6120A2 evaluation module (EVM). This users guide includes EVM
description, performance specifications, board layout, bill of materials (BOM),
and schematic diagram.
How to Use This Manual
This document contains the following chapters:
-Chapter 1 – Introduction
-Chapter 2 – Getting Started
-Chapter 3 – Customizing the EVM
-Chapter 4 – EVM Circuit and Layout
Related Documentation From Texas Instruments
SLOS431 − TPA6120A2 data sheet
If you need Assistance
Contact your local TI sales representative.
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
tested for compliance with the limits of computing devices pursuant to subpart
J of part 15 of FCC rules, which are designed to provide reasonable protection
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.

iv

Contents
v

1 Introduction 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1 Description 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Performance Specification Summary 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Getting Started 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Power Supply 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Inputs and Outputs 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Power Up 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Customizing the EVM 3-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Inverting Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Differential Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Special Note on Gain and Input Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Single Power Supply Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 EVM Circuit and Layout 4-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1 TPA6120A2 EVM Top Layer 4-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 TPA6120A2 EVM Bottom Layer 4-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Component Selection 4-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Input Bias Voltage 4-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Schematic 4-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.6 Bill of Materials 4-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Contents
vi
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2−1 Top Layer With Numbered Callouts 2-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4−1 Top Layer of the TPA6120A2 EVM 4-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4−2 Bottom Layer of the TPA6120A2 EVM 4-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4−3 TPA6120A2 EVM Schematic 4-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1−1 TPA6120A2 EVM Performance Specifications 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4−1 TPA6120A2 EVM Bill of Materials 4-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1
Introduction

The TPA6120A2 is a high-fidelity audio amplifier. The amplifier can operate
from a split power supply, and is designed for low noise, high dynamic range
performance.
Topic Page
1.1 Description 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Performance Specifications 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1

Description
1-2
1.1 Description
The TPA6120A2 EVM is designed to operate specifically with a split power
supply, and is configured such that both left and right channels have a
noninverting gain of 2 V/V. The output signal is routed into RCA jacks J1 and
J2, as well as the 1/4 inch headphone jack, J10. The EVM is approximately
3 inches x 3 inches square, and comes complete with standoffs.
1.2 Performance Specifications
Table 1−1.TPA6120A2 EVM Specifications
TPA6120A2
Supply voltage range, VCC ±5 V to ±15
Power supply current rating required 1 A
Continuous output power, Po: 32-Ωstereo, VCC = ±12 V 2 W
Audio input voltage, VI−VCC to VCC
Minimum load impedance, Z(L) 8 Ω
CAUTION
1) Accidental swapping of supply polarities causes damage to the
device and can cause damage to the other components on the
board.
2) Do not short the outputs of the TPA6120A2 to either the positive or
negative supply when operating with a split power supply. When
operating with a single power supply, do not short the outputs to the
positive supply. This damages the device.

2-1
Getting Started
 
Follow these steps to use the TPA6120A2 EVM in its original configuration.
No soldering is necessary. Connection to the TPA6120A2 EVM can be made
with banana plugs, RCA jacks, and a 1/4 inch headphone jack. See Figure 2−1
for an illustration of the top layer.
Topic Page
2.1 Power Supply 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Inputs and Outputs 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Power Up 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 2

Power Supply
2-2
2.1 Power Supply
1) Make sure all external power supplies are turned off.
2) Connect an external power supply with the positive voltage set between
5 V and 15 V to the terminal marked +12 V (J8) on the EVM.
3) Connect the negative voltage to the terminal marked −12 V (J9), making
sure the negative voltage is set to the same magnitude as that of the
positive (i.e., ±5 V, ±12 V, ±15 V).
4) Connect the ground of the external supply to the terminal marked GND
(J7) on the EVM.
2.2 Inputs and Outputs
5) Ensure the signal source is turned off or set to a minimum.
6) Connect the left signal source to the RCA jack labeled LIN+ (J5), and the
right signal source to the RCA jack labeled RIN+ (J6).
7) Insert headphones into 1/4 inch headphone jack, J10.
8) If desired, RCA Jacks J1 and J2 may be used instead of the headphone
jack for load driving purposes. The RCA jacks and the headphone jack
should not be used together when both are driving a load. One may be
used to drive a load while the other is used for measurement purposes.
2.3 Power Up
9) Verify correct voltage polarity on the supplies.
10) Make sure the signal source is going into the positive inputs only. Do NOT
connect anything to the negative inputs—this shorts the output of the
signal source directly to ground (see schematic in EVM Circuit and Layout
section)
11) Turn on the power supply.
12) Turn on the signal source.
13) Adjust signal source level as needed.

Power Up
2-3
Getting Started
Figure 2−1.Top Layer With Numbered Callouts (From paragraphs 2.1 through 2.3)
878
2
9
6
3
9
6
4

Power Up
2-4
(This page has been left blank intentionally.)

3-1
Customizing The EVM
  
The TPA6120A2 EVM comes in a noninverting configuration with a gain of
2 V/V. However, the EVM is designed to be flexible, and can be converted to
operate in inverting and differential configurations. The TPA6120A2 EVM can
also be operated in a single power supply configuration.
Topic Page
3.1 Inverting Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Differential Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Special Note on Gain and Input Configurations 3-2. . . . . . . . . . . . . . . . . .
3.4 Single Power Supply Configuration 3-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 3

Inverting Configuration
3-2
3.1 Inverting Configuration
The TPA6120A2 EVM can be converted to operate in an inverting gain
configuration. To do this, it is necessary to remove resistors R11 and R12, then
connect the audio source to RCA jacks LIN− (J3) and RIN− (J4) instead of LIN+
(J5) and RIN+ (J6). With the feedback and input resistors already in place on
the EVM, the gain is set to −1 V/V (RF/RI).
3.2 Differential Configuration
The TPA6120A2 EVM can also be converted to operate in a differential input
configuration. Remove resistors R11 and R12. Resistors R9 and R10 must be
removed and replaced with resistors whose values match those of resistors
R3 and R4, respectively. The 49.9-Ωinput series resistors, R7 and R8 must
likewise be removed and replaced with resistors whose values match those
of input resistors R1 and R2, respectively. Both positive and negative input
jacks should be used. Assuming the feedback resistors R9 and R3 are equal,
and R10 and R4 are equal, and the input resistors R7 and R1 are equal, and
R8 and R2 are equal, the gain is set by the following formula:
Gain +2 RF
RI
3.3 Special Note on Gain and Input Configurations
The TPA6120A2 high-fidelity audio power amplifier has two separate
channels, left and right. It is not necessary to operate each channel in the same
configuration. For test purposes, it may be desirable to operate the left channel
with a noninverting configuration, and the right channel with an inverting
configuration. One channel may be configured to operate with differential
inputs while the other channel with single-ended inputs. The TPA6120A2 EVM
allows for this flexibility. From a listening standpoint, the best audio
performance is achieved when both channels are operated with the same
configuration. In this case, there is no sound difference between the left and
right channels for the human ear to detect.
3.4 Single Power Supply Configuration
The TPA6120A2 EVM was not optimized for single power supply operation.
To operate in this mode, the −12-V terminal must be connected to GND.
DC-blocking capacitors must be used at the outputs to prevent large amounts
of dc current from flowing through the headphones due to the high midrail bias.
Likewise, dc-blocking capacitors must be used at the input. Resistors R11 and
R12, and resistors R9 and R10 must be removed. The positive input nodes
must be biased to midrail. Resistors R9 and R10 tie the positive node to
ground.

4-1
EVM Circuit and Layout
   
The TPA6120A2 EVM layout was carefully planned to minimize the
capacitance and inductance detected by the output and input pins of the
amplifier. Test points are available, but intentionally left unpopulated to keep
signal interference as low as possible.
This chapter includes the EVM layout, the TPA6120A2 EVM component
selection, schematic, and bill of materials.
Topic Page
4.1 TPA6120A2 EVM Top Layer 4-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 TPA6120A2 EVM Bottom Layer 4-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Component Selection 4-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Input Bias Voltage 4-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Schematic 4-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.6 Bill of Materials 4-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 4

TPA6120A2 EVM Top Layer
4-2
4.1 TPA6120A2 EVM Top Layer
Figure 4−1 shows the top layer of the TPA6120A2 EVM. The RCA jacks at the
inputs are configured to short to ground when no plug is inserted. The
noninverting configuration of the EVM requires that RIN− and LIN− be at
ground. Rather than have the signal go through the long signal trace to get to
the input jacks, 0-Ωresistors R11 and R12 are used to provide a connection
to ground much closer to the device.
A star point for ground should be chosen. For the TPA6120A2 EVM, the
ground terminal of the board is (J7). Current paths to the star ground should
be as direct as possible.
Figure 4−1.Top Layer of the TPA6120A2 EVM

TPA6120A2 EVM Bottom Layer
4-3
EVM Circuit and Layout
4.2 TPA6120A2 EVM Bottom Layer
Figure 4−2 shows the bottom layer of the TPA6120A2 EVM. Note that the
copper has been removed from around the capacitive sensitive nodes. It is
important to remember that the thermal pad on the underside of the IC must
be properly soldered to the board at all times.
Figure 4−2.Bottom Layer of the TPA6120A2 EVM

Component Selection
4-4
4.3 Component Selection
The TPA6120A2 is a high-fidelity audio amplifier. The composition of
components is important when dealing with high fidelity. The best practice is
to operate the device with a split power supply. This eliminates the need for
capacitors in the signal path, which can introduce distortion. Capacitors can
also fail after a certain period of time. The failure mode of many capacitors is
to essentially turn into a short. If capacitors must be used in the signal path
because the device is being used in a single power supply configuration,
polystyrene and PPS film capacitors are good choices.
Thin film resistors have excellent noise and distortion performance.
4.4 Input Bias Voltage
The TPA6120A2 EVM is designed to keep a constant dc voltage on the
positive input pins of the amplifier. This is done with resistors R9 and R10
which effectively tie the positive input pins to ground. This is necessary in most
applications to protect the system and its components from unexpectedly high
dc currents, and to prevent damage to headphones from both large continuous
dc currents and a large POP.
When a source is not connected to the positive node, and the positive node
is not tied to ground, it floats, typically up to the rail. A 12-V offset with a 32-Ω
load can draw up to 375 mA of current, depending on the size of the output
series resistor. When a source is then connected, or turned on and thus taken
out of a high impedance state, the offset voltage quickly drops to near 0 V. This
large, fast change can cause a loud, potentially headphone damaging POP.
The solution is to keep the positive input pin of the amplifier at a constant
voltage, regardless of the state of the audio source.
With headphones, permanent damage to the voice coil can begin to occur
when the dc voltage across them exceeds 100 mV. The maximum input bias
current of the TPA6120A2 is 12 µA. Therefore, the maximum output offset with
the audio source off is:
ǒ(12 mA R9) *ǒ12 mA RFøRIǓǓ Gain
Once the audio source is turned on, the output offset voltage drops to just a
few millivolts.
The value for R9 must be chosen carefully. The value has a direct impact on
the output offset voltage and the loading of the audio source. In the
configuration of the TPA6120A2EVM, where the input and feedback resistors
(R1 and R3) are each 1-kΩ, a 500-Ωresistor would be the best choice for offset
performance. However, a load of this size can degrade the performance of the
audio source. The audio source should have no problems driving a large load
such as a 100-kΩresistor. However, a load of this size can cause as much as
2.4 V of output offset voltage (when the source is left floating).