![](http://datasheet.mmic.net.cn/130000/TPA3123D2PWPG4_datasheet_5021764/TPA3123D2PWPG4_15.png)
LOUT /ROUT
L
filter
C
filter
LOUT
L
filter
C
filter
L
filter
C
filter
ROUT
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SLOS541C – JULY 2007 – REVISED AUGUST 2010
Output Filter and Frequency Response
For the best frequency response, a flat-passband output filter (second-order Butterworth) may be used. The
output filter components consist of the series inductor and capacitor to ground at the LOUT and ROUT pins.
There are several possible configurations depending on the speaker impedance, and whether the output
configuration is single ended (SE) or bridge-tied load (BTL).
Table 4 lists the recommended values for the filter
components. It is important to use a high-quality capacitor in this application. A rating of at least X7R is required.
Table 4. Recommended Filter Output Components
Output Configuration
Speaker Impedance (
)
Filter Inductor (mH)
Filter Capacitor (nF)
4
22
680
Single Ended (SE)
8
47
390
4
10
1500
Bridge Tied Load (BTL)
8
22
680
Figure 25. BTL Filter Configuration
Figure 26. SE Filter Configuration
Power-Supply Decoupling, CS
The TPA3123D2 is a high-performance CMOS audio amplifier that requires adequate power-supply decoupling
to ensure that the output total harmonic distortion (THD) is as low as possible. Power-supply decoupling also
prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is
achieved by using two capacitors of different types that target different types of noise on the power-supply leads.
For higher-frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR)
ceramic capacitor, typically 0.1 mF to 1 mF, placed as close as possible to the device VCC lead works best. For
filtering lower frequency noise signals, a larger aluminum electrolytic capacitor of 470 mF or greater placed near
the audio power amplifier is recommended. The 470-mF capacitor also serves as local storage capacitor for
supplying current during large signal transients on the amplifier outputs. The PVCC terminals provide the power
to the output transistors, so a 470-mF or larger capacitor should be placed on each PVCC terminal. A 10-mF
capacitor on the AVCC terminal is adequate. These capacitors must be properly derated for voltage and ripple
current rating to ensure reliability.
BSN and BSP Capacitors
The half H-bridge output stages use only NMOS transistors. Therefore, they require bootstrap capacitors for the
high side of each output to turn on correctly. A 220-nF ceramic capacitor, rated for at least 25 V, must be
connected from each output to its corresponding bootstrap input. Specifically, one 220-nF capacitor must be
connected from LOUT to BSL, and one 220-nF capacitor must be connected from ROUT to BSR.
The bootstrap capacitors connected between the BSx pins and their corresponding outputs function as a floating
power supply for the high-side N-channel power MOSFET gate-drive circuitry. During each high-side switching
cycle, the bootstrap capacitors hold the gate-to-source voltage high enough to keep the high-side MOSFETs
turned on.
Copyright 2007–2010, Texas Instruments Incorporated
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