Datasheet

LOUT /ROUT
L
filter
C
filter
LOUT
L
filter
C
filter
L
filter
C
filter
ROUT
Power-Supply Decoupling, C
S
BSN and BSP Capacitors
VCLAMP Capacitor
BYPASS Capacitor Selection
TPA3125D2
SLOS611 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
Figure 27. BTL Filter Configuration Figure 28. SE Filter Configuration
The TPA3125D2 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 µ F to 1 µ F, placed as close as possible to the device PV
CC
pin works best. For
filtering lower frequency noise signals, a larger aluminum electrolytic capacitor of 470 µ F or greater placed near
the audio power amplifier is recommended. The 470- µ F 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- µ F or larger capacitor should be connect to each PVCC terminal. A 10- µ F
capacitor on the AVCC terminal is adequate. These capacitors must be properly derated for voltage and
ripple-current rating to ensure reliability.
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.
To ensure that the maximum gate-to-source voltage for the NMOS output transistors is not exceeded, one
internal regulator clamps the gate voltage. One 1- µ F capacitor must be connected from VCLAMP (pin 11) to
ground and must be rated for at least 16 V. The voltages at the VCLAMP terminal may vary with V
CC
and may
not be used for powering any other circuitry.
The scaled supply reference (VBYP) nominally provides an AVCC/8 internal bias for the preamplifier stages. The
external capacitor for this reference, C
BYP
, is a critical component and serves several important functions. During
start-up or recovery from shutdown mode, C
BYP
determines the rate at which the amplifier starts. The start up
time is proportional to 0.5 s per microfarad. Thus, the recommended 1- µ F capacitor results in a start-up time of
approximately 500 ms. The second function is to reduce noise produced by the power supply caused by coupling
with the output drive signal. This noise could result in degraded power-supply rejection and THD+N.
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