This user's guide describes the characteristics, operation, and use of the TPA3251 evaluation module
(EVM). A complete printed-circuit board (PCB) description, schematic diagram, and bill of materials are
also included.
10TPA3251EVM Bill of Materials ........................................................................................... 19
Trademarks
PurePath is a trademark of Texas Instruments.
CoilCraft is a trademark of Coilcraft, Incorporated.
Molex is a trademark of Molex, LLC.
All other trademarks are the property of their respective owners.
This section describes the necessary hardware, connections, configuration, and steps to quick start the
EVM into bridge-tied load (BTL) mode with stereo audio playing out of two speakers.
1.1Required Hardware
The EVM requires the following hardware:
•TPA3251EVM (AMPS030-001) power supply 18-V to 36-V DC, 15 A
•Two 2-Ω to 8-Ω, 100-W speakers or resistor loads
•Four speaker or banana cables
•RCA input cables
•Analog output audio source
1.2Connections and Board Configuration
Figure 2 and Figure 3 show both sides of the EVM board.
b. Connect the positive RCA male jack to the female RCA jack input C/CD (J18-RED) and
connect the negative RCA male jack to the female RCA jack input D (J15-BLACK).
c. Analog-Input Board (AIB) input: Set J26, J27, J34, and J35 to AIB.
10. Power up the power supply after correctly making all the connections. The 3.3-V and 12-V LEDs
(GREEN) then illuminate.
11. Set S1 to the NORMAL position.
12. The CLIP_OTW (ORANGE) and FAULT (RED) LEDs must be off if the audio source is off.
Table 1 lists the jumper configurations in BTL mode.
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Table 1. Jumper Configurations (BTL Mode)
JumperSettingConfiguration for BTL
J29INPVDD to 15-V BUCK
J32IN12-V LDO to 12-V TERM
J33IN3.3-V LDO to 3.3-V TERM
J36IN12-V LDO to GVDD
J163 to 4MASTER MODE 600kHz
J22INOUTA CAP SHUNT
J23INOUTB CAP SHUNT
J24INOUTC CAP SHUNT
J25INOUTD CAP SHUNT
J52 to 3M1-L
J62 to 3M2-L
J7OUTPBTL SELECT INC
J8OUTPBTL SELECT IND
J41 to 2INA/B SE INPUT
J191 to 2INC/D SE INPUT
J261 to 2INC-SEL RCA
J271 to 2IND-SEL RCA
J341 to 2INA-SEL RCA
J351 to 2INB-SEL RCA
J21OUTC_START
The user can configure the TPA3251EVM for four different output operations. The 2.0 BTL configuration is
the default set up of the TPA3251EVM as described in Section 1.2. The remaining three configurations
are 2.1 BTL plus two SE outputs, 0.1 PBTL output, and 4.0 SE outputs.
Setup By Mode
Table 2. Mode Selection Pins
Mode Pins
M2M1
Input ModeOutput ConfigurationDescription
002N + 12 x BTLStereo BTL output configuration
012N-1N + 11 x BTL + 2 × SE2.1 BTL + SE mode
102N + 11 × PBTLParallel BTL configuration; connect INPUT_C
2.1BTL Mode (Two-Speaker Output)
This mode is the same as described in Section 1.
2.1.1Performance Data (BTL Mode)
All measurements are taken at an audio frequency = 1 kHz, PVDD_X = 36 V, RL = 4 Ω, fS = 600 kHz,
ROC = 22 kΩ, Output filter: L = 7 μH, C = 0.68 µF, with AES17 + AUX-0025 measurement filters.
Figure 4. AIB Input: THD+N vs FrequencyFigure 5. AIB Input: THD+N vs Power
Figure 6. Molex™ Input: THD+N vs FrequencyFigure 7. Molex Input: THD+N vs Power
Figure 8. RCA Input: THD+N vs FrequencyFigure 9. RCA Input: THD+N vs Power
2.2BTL MODE (Three-Speaker Output)
OUTC and OUTD are the SE output channels and OUTA and OUTB are the BTL channels for 2.1
operations. OUTC and OUTD can only be in DIFF input mode.
1. Set J6 to L and J5 to H.
2. Remove jumpers J24 and J25.
3. Connect the positive side of the left channel load to OUTC (J2- RED) terminal and the negative side of
the left channel load to the GND (J20) terminal.
4. Connect the positive side of the right channel load to OUTD (J2-BLACK) terminal and the negative
side of the right channel load to the GND (J20) terminal.
5. Connect the positive terminal to OUTA (J9-RED) and the negative terminal to OUTB (J9-BLACK).
6. Set the J19 jumper position to DIFF.
7. Input configuration:
a. SE inputs: Connect the RCA male jack to the female RCA jack input A/AB (J3-RED) and set the J4
jumper positions to SE. Set J26, J27, J34, and J35 to RCA.
b. Differential inputs: Connect the positive RCA male jack to the female RCA jack input A/AB ( J3-
RED) and connect the negative RCA male jack to the female RCA jack input B (J14-BLACK) and
set the J4 jumper positions to DIFF. Set J26, J27, J34, and J35 to RCA.
c. AIB inputs: Set J26, J27, J34, and J35 to AIB.
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2.3PBTL Mode (One-Speaker Output)
This mode uses all four half bridges for a mono output, allowing for the maximum power output from the
device across one load.
6
TPA3251 Evaluation Module
Table 3. Jumper Configurations (2.1 BTL Mode)
JumperSettingComment
J29INPVDD to 15-V BUCK
J32IN12-V LDO to 12-V TERM
J33IN3.3-V LDO to 3.3-V TERM
J36IN12-V LDO to GVDD
J163 to 4MASTER MODE 600kHz
J22INOUTA CAP SHUNT
J23INOUTB CAP SHUNT
J24OUTOUTC CAP SHUNT
J25OUTOUTD CAP SHUNT
J51 to 2M1 – H
J62 to 3M2 – L
J7OUTPBTL SELECT INC
2. Connect the positive side of the load to OUTA (J9-RED) and OUTC (J2-RED) terminals (OUTA and
OUTC shorted).
3. Connect the negative side of the load to OUTB (J9-BLACK) and OUTD (J2-BLACK) terminals (OUTB
and OUTD shorted).
4. Install PBTL jumpers J7 and J8 (pulls input C and input D to GND).
5. Input configuration:
a. SE inputs: Connect the RCA male jack to the female RCA jack input A/AB (J3-RED) and set the J4
jumper positions to SE. Set J26, J27, J34, and J35 to RCA.
b. Differential inputs: Connect the positive RCA male jack to the female RCA jack input A/AB (J3-
RED) and connect the negative RCA male jack to the female RCA jack input B (J14-BLACK). Set
the J4 jumper position to DIFF, and set J26, J27, J34, and J35 to RCA.
c. AIB input: Set J26, J27, J34, and J35 to AIB.
Table 4. Jumper Configuration (PBTL Mode)
JumperSettingComment
J29INPVDD to 15-V BUCK
J32IN12-V LDO to 12-V TERM
J33IN3.3-V LDO to 3.3-V TERM
J36IN12-V LDO to GVDD
J163 to 4MASTER MODE 600kHz
J22INOUTA CAP SHUNT
J23INOUTB CAP SHUNT
J24INOUTC CAP SHUNT
J25INOUTD CAP SHUNT
J52 to 3M1 – L
J61 to 2M2 – H
J7INPBTL SELECT INC – GND
J8INPBTL SELECT IND – GND
J41 to 2INA/B SE INPUT
J191 to 2INC/D SE INPUT
J261 to 2INC-SEL RCA
J271 to 2IND-SEL RCA
J341 to 2INA-SEL RCA
J351 to 2INB-SEL RCA
J21OUTC_START
(1)
INA and INB are the inputs for PBTL, and INC and IND are grounded
for PBTL operation.
Setup By Mode
(1)
2.3.2Performance Data (PBTL Mode)
All measurements are taken at an audio frequency = 1 kHz, PVDD_X = 36 V, RL = 4 Ω, fS = 600 kHz,
ROC = 22 kΩ, Output filter: L = 7μH, C = 0.68 µF, with AES17 + AUX-0025 measurement filters.
ii. Connect the male RCA jack to the female RCA jack input B (J14-BLACK) for the OUTB
speaker.
iii. Connect the male RCA jack to the female RCA jack input C/CD (J18-WHITE) for the OUTC
speaker.
iv. Connect the male RCA jack to the female RCA jack input D (J15-BLUE) for the OUTD
speaker.
b. AIB input: Set J26, J27, J34, and J35 to AIB.
Table 5. Jumper Configuration (SE Mode)
JumperSettingComment
J29INPVDD to 15-V BUCK
J32IN12-V LDO to 12-V TERM
J33IN3.3-V LDO to 3.3-V TERM
J36IN12-V LDO to GVDD
J163 to 4MASTER MODE 600kHz
J22OUTOUTA CAP SHUNT
J23OUTOUTB CAP SHUNT
J24OUTOUTC CAP SHUNT
J25OUTOUTD CAP SHUNT
J51 to 2M1 – H
J61 to 2M2 – H
J7OUTPBTL SELECT INC
J8OUTPBTL SELECT IND
J42 to 3INA/B DIFF INPUT
J192 to 3INC/D DIFF INPUT
J261 to 2INC-SEL RCA
J271 to 2IND-SEL RCA
J341 to 2INA-SEL RCA
J351 to 2INB-SEL RCA
J21INC_START
NOTE: The performance of the TPA3251EVM/TPA3251D2DDV is dependent on the power supply.
Design the power supply with margins that can deliver the required power. Some lowfrequency applications can require additional bulk capacitance. Replacing the bulk capacitors
on the TPA3251EVM with 3300 µF or more capacitance can be necessary depending on the
power supply used.
2.4.1Performance Data (SE Mode)
All measurements are taken at audio frequency = 1 kHz, PVDD_X = 36 V, RL = 4 Ω, fS = 600 kHz, ROC
= 22 kΩ, Output filter: L = 7 μH, C = 0.68 µF, with AES17 + AUX-0025 measurement filters.
Figure 16. AIB Input: THD+N vs FrequencyFigure 17. AIB Input: THD+N vs Power
Figure 18. Molex Input: THD+N vs FrequencyFigure 19. Molex Input: THD+N vs Power
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Figure 20. RCA Input: THD+N vs FrequencyFigure 21. RCA Input THD+N vs Power
3Hardware Configuration
3.1Indicator Overview (OTW_CLIP and FAULT)
The TPA3251EVM is equipped with LED indicators that illuminate when the FAULT or CLIP_OTW pin (or
both) goes low. See Table 6 and TPA3251 175-W Stereo, 350-W Mono PurePath™ Ultra-HD Analog-
Input Class-D Amplifier for more details on which events trigger the pins to go low.
FAULTOTW_CLIPDescription
00
00OLP or UVP; junction temperature higher than 125°C (overtemperature warning)
10
01OLP or UVP; junction temperature lower than 125°C
10Junction temperature higher than 125°C (overtemperature warning)
11Junction temperature lower than 125°C and no OLP or UVP faults (normal operation)
TPA3251 Evaluation Module
Table 6. Fault and Clip Overtemperature Status
Overtemperature (OTE), overload (OLP), or undervoltage (UVP) junction temperature higher than
125°C (overtemperature warning)
The TPA3251EVM offers a hardware-trimmed oscillator frequency by through the external control of the
FREQ_ADJ pin. Use the frequency adjust to reduce interference problems while using a radio receiver
tuned within the AM band and change the switching frequency from nominal values to lower values (see
Table 7). Choose these values such that the nominal- and the lower-value switching frequencies together
result in the fewest cases of interference throughout the AM band. Select the oscillator frequency based
on the value of the FREQ_ADJ resistor connected to GND in master mode.
Table 7. Frequency Adjust Master Mode Selection
ModeSwitching FrequencyResistor to GNDPin Configuration
MASTER MODE 600 kHz600 kHz10 kΩ3 to 4
MASTER MODE 500 kHz500 kHz20 kΩ5 to 6
MASTER MODE 450 kHz450 kHz30 kΩ7 to 8
For slave-mode operation, turn off the oscillator by pulling the FREQ_ADJ pin to 3.3 V. This action
configures the OSC_I/O pins as inputs, which are to be slaved from an external differential clock. In a
master and slave system, interchannel delay is automatically set up between the switching phases of the
audio channels, which can be illustrated by no idle channels switching at the same time. This setup does
not influence the audio output; rather, only the switch timing to minimize noise coupling between audio
channels through the power supply. In turn, this process optimizes audio performance and results in better
operating conditions for the power supply. The interchannel delay is setup for a slave device depending on
the polarity of the OSC_I/O connection, such that slave mode 1 is selected by connecting OSC_I/O of the
master device in phase with OSC_I/O of the slave device (+ to + and – to –), while slave mode 2 is
selected by connecting the OSC_I/Os out of phase (+ to – and – to +).
Hardware Configuration
3.3TPA3251EVM Overcurrent Adjust
The TPA3251EVM offers the ability for the user to change the current limit by changing R13 as well as
having two different protection modes, Cycle by Cycle Current Control (CB3C) and Latching Shutdown
(Latched OC). For CB3C operations, the resistance must be a value of 22 kΩ to 30 kΩ. For Latched OC
operations, the resistance must be a value of 47 kΩ to 64 kΩ. By default, the resistor R13 is 22 kΩ.
Table 8 shows a few resistance values and their corresponding OC threshold and OC protection mode.
Table 8. Overcurrent Protection Selection
OC_ADJ Resistor
Value
22 kΩCB3C16.3 A
24 kΩCB3C15.1 A
27 kΩCB3C13.5 A
30 kΩCB3C12.3 A
47 kΩLatched OC16.3 A
51 kΩLatched OC15.1 A
56 kΩLatched OC13.5 A
64 kΩLatched OC12.3 A
Protection ModeOC Threshold
3.4TPA3251EVM Single-Ended and Differential Inputs
The TPA3251EVM supports both differential and SE inputs. For SE inputs, set either the J4 or J19 jumper
(or both) to the SE position so that the TPA3251EVM uses the NE5532 operational amplifier (op amp) to
convert the SE input signal to differential to properly drive the differential inputs of the TPA3251 device.
Use input RCA jack J3 to provide INA and INB inputs. Use RCA jack J18 to provide INC and IND inputs
with SE inputs. For differential input operation, set either the J4 or J19 jumpers (or both) to the DIFF
position. The TPA3251EVM uses the NE5532 to buffer the differential input signal to the differential inputs
of the TPA3251 device. Use input RCA jack J3 to provide INA, RCA jack J14 to provide INB, RCA jack
J18 to provide INC, and RCA jack J15 to provide IND with differential inputs.
NOTE: The SE input settings on the TPA3251EVM must only be used for channels with output
configuration BTL or PBTL, not SE. For SE output configuration, the user must set either
jumper J4 or J19 (or both) for that channel to the DIFF position so that the input signal INx is
mapped directly to OUTx.
3.5Input Connectors
The TPA3251EVM supports three different input connectors. J3, J14, J15, and J18 are RCA connectors;
J10 and J12 are Molex connectors; and J28 is the AIB connector with J30 being the AIB alignment
connection. Table 9 shows the AIB pinout in detail.
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Table 9. AIB Connector (J28) Pinout
Pin
No.
1Amp Out ASpeaker-level output from audio class-D EVM (SE or one side of BTL)O
2Amp Out BSpeaker-level output from audio class-D EVM (SE or one side of BTL)O
3PVDD
4GNDGround reference between audio plug-in module and audio class-D EVM
5NC
6NC
73.3 V3.3-V supply from EVM; used for powering audio plug-in moduleO
83.3 V3.3-V supply from EVM; used for powering audio plug-in moduleO
912 V12-V supply from EVM; used for powering audio plug-in moduleO
10EN and ResetAssert enable and reset control for audio class-D EVM (active low)I
11Analog IN_AAnalog audio input A (analog in EVM), Master I2S bus (digital in EVM)I
12NC
13Analog IN_BAnalog audio input B (analog in EVM), bit clock I2S bus (digital in EVM)I
14CLIP_OTW
15Analog IN_CAnalog audio input C (analog in EVM), frame clock I2S bus (digital in EVM)I
16FAULTFault detection from audio Class-D EVM (active low)O
17Analog IN_DAnalog audio Input D (analog in EVM), data in I2S bus (digital in EVM)I
18NC
19NC
20NC
21GNDGround reference between audio plug-in module and audio class-D EVM
22GNDGround reference between audio plug-in module and audio class-D EVM
23NC
24NC
25NC
26NC
27Amp Out CSpeaker-level output from audio class-D EVM (SE or one side of BTL)O
28Amp Out DSpeaker-level output from audio class-D EVM (SE or one side of BTL)O
FunctionDescription
PVDD voltage supply from audio Class-D EVM (variable voltage depending
on Class-D EVM use)
Clipping detection, overtemperature warning, or both from audio class-D EVM
(active low)
The EVM power section is self-contained with all the necessary onboard voltages generated from the
main PVDD (J1) power input. The PVDD is reduced to 15 V and then used to generate the remaining
required board voltages of 12 V, 5 V, and 3.3 V. Low-dropout linear regulators (LDOs) generate supplies
going to the TPA3221 device itself to reduce the chance of extra added noise. LEDs are provided on the
5-V and 3.3-V supplies so that the user can verify that the EVM is powered (see Figure 22).
3.7LC Filter Overview
Included near the output of the TPA3251 device are four output LC filters. These output filters filter the
pulse-width modulation (PWM) output, leaving only the audio content at high power, which is fed to the
speakers. The board uses a CoilCraft™ 7-µH inductor and a 0.68-µF film capacitor to form this LC filter.
Using the equations listed in LC Filter Design Application Report , the low-pass filter cutoff is calculated as
follows in Equation 1:
Hardware Configuration
Figure 22. EVM Power Tree
Figure 23. BTL LC Frequency ResponseFigure 24. SE LC Frequency Response
3.8Post-Filter Feedback (PFFB)
The TPA3251EVM has the footprints available to implement post filter feedback to improve the audio
performance of the TPA3251 amplifier. For more details on benefits and implementation, see TPA324x
The TPA3251EVM includes RESET supervision so that the TPA3251 device remains in reset until all the
power rails are up and stable. The RESET supervisor also ensures that the device is put into reset if one
of the power rails experiences a brownout. This circuit combined with the RESET switch (S1) help ensure
that the TPA3251 can be placed in reset easily as needed or automatically if there is a power supply
issue.
3.10Op Amp versus Direct Drive
The op amps are used to change a single-ended input into a differential input. By default, the gain of the
op amps are set for unity gain; however, this can be modified to increase or decrease the gain through the
op amps. One way to bypass the op amps for a more direct connection is using the AIB.
4EVM Design Documents
This section contains the TPA3251EVM board layout, schematics, and bill of materials (BOM).
4.1TPA3251EVM Board Layouts
Figure 25 and Figure 26 illustrate the EVM board layouts.
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