TAS5704 Datasheet, PDF (24/34 Pages) Texas Instruments – 20-W Stereo Digital Audio Power Amplifier With Feedback

TAS5704
SLOS563 – MARCH 2008
OUTA
L_filter
C_filter
OUTA
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L_filter
C_filter
OUTB
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C_filter
Figure 29. BTL Filter Configuration
Figure 30. SE Filter Configuration
POWER-SUPPLY DECOUPLING, C_S
The TAS5704 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 µF to 1 µF, placed as close as possible to the device V_CC lead works best. For
filtering lower frequency noise signals, a larger aluminum electrolytic capacitor of 220 µF or greater placed near
the audio power amplifier is recommended. The 220-µF 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 220-µF or larger capacitor should be placed on each PVCC terminal. A 10-µF
capacitor on the AVCC terminal is adequate. These capacitors must be properly derated for voltage and
ripple-current rating to ensure reliability.
BOOTSTRAP 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.
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.
VCLAMP CAPACITOR
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-µF capacitor must be connected from each VCLAMP (terminal)
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.
VBYP CAPACITOR SELECTION
The scaled supply reference (BYPASS) 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 in single-ended mode (SE/BTL = DVDD). Thus, the recommended
1-µF capacitor results in a start-up time of approximately 500 ms (SE/BTL = DVDD). 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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