Datasheet

Common Mode Resonance
Power-Supply Decoupling, C
S
BSN and BSP Capacitors
VCLAMP Capacitor
VBYP Capacitor Selection
TAS5602
www.ti.com ................................................................................................................................................... SLAS593B – JUNE 2008 – REVISED NOVEMBER 2008
The BTL filter shown above is an excellent, low-cost way to attenuate the high frequency energy from the Class
D output stage while passing the audio signal cleanly to the speakers. However, at the resonant frequency of the
LC combination, ringing can occur as a common mode output from the amplifier. This ringing can result in
resonant frequency energy appearing on the speaker leads and can also cause the power dissipation in the filter
L and C to increase.
To keep the common mode ringing to a reasonable level, some series resistance should be designed into the
circuit. Testing and simulations have shown that 75 m Ω of series resistance in the path which includes the filter L
and C is enough to control the common mode ringing. The series resistance of the filter coil and the ESR of the
cap can be used to form the resistance. The copper traces in series with the filter capacitor are another good
place to add some series resistance to the circuit.
Another way to improve the common mode ringing is to add an RC network to ground on each output. Testing
has shown that a series network consisting of 100 Ω and 47 nF is enough to damp the ringing for most speaker
systems.
The TAS5602 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 V
CC
lead works best. For
filtering lower frequency noise signals, a larger aluminum electrolytic capacitor of 220 µ F or greater placed near
the audio power amplifier is recommended. The 220- 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 220- µ F or larger capacitor should be placed on 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.
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 each VCLAMP (terminal)
to ground and must be rated for at least 16 V. The voltages at the VCLAMP terminal vary with V
CC
and may not
be used for powering any other circuitry.
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- µ F 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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