TPA3121D2

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SLOS537B – MAY 2008 – REVISED JANUARY 2014

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 VCLAMP (pin 11) to

ground and must be rated for at least 16 V. The voltages at the VCLAMP terminal may vary with VCC and may

not be used for powering any other circuitry.

VBYP Capacitor Selection

The scaled supply reference (VBYP) nominally provides an AVCC/8 internal bias for the preamplifier stages. The

external capacitor for this reference (CBYP) is a critical component and serves several important functions. During

start-up or recovery from shutdown mode, CBYP determines the rate at which the amplifier starts. The start up

time is proportional to 0.5 s per microfarad. Thus, the recommended 1-

μF 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.

The circuit is designed for a CBYP value of 1 μF for best pop performance. The input capacitors should have the

same value. A ceramic or tantalum low-ESR capacitor is recommended.

SHUTDOWN OPERATION

The TPA3121D2 employs a shutdown mode of operation designed to reduce supply current (ICC) to the absolute

minimum level during periods of nonuse for power conservation. The SHUTDOWN input terminal should be held

high (see specification table for trip point) during normal operation when the amplifier is in use. Pulling

SHUTDOWN low causes the outputs to mute and the amplifier to enter a low-current state. Never leave

SHUTDOWN unconnected, because amplifier operation would be unpredictable.

For the best power-up pop performance, place the amplifier in the shutdown or mute mode prior to applying the

power-supply voltage.

MUTE Operation

The MUTE pin is an input for controlling the output state of the TPA3121D2. A logic high on this terminal causes

the outputs to run at a constant 50% duty cycle. A logic low on this pin enables the outputs. This terminal may be

used as a quick disable/enable of outputs when changing channels on a television or transitioning between

different audio sources.

The MUTE terminal should never be left floating. For power conservation, the SHUTDOWN terminal should be

used to reduce the quiescent current to the absolute minimum level.

USING LOW-ESR CAPACITORS

Low-ESR capacitors are recommended throughout this application section. A real (as opposed to ideal) capacitor

can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor

minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance,

the more the real capacitor behaves like an ideal capacitor.

SHORT-CIRCUIT PROTECTION

The TPA3121D2 has short-circuit protection circuitry on the outputs that prevents damage to the device during

output-to-output shorts and output-to-GND shorts after the filter and output capacitor (at the speaker terminal.)

Directly at the device terminals, the protection circuitry prevents damage to device during output-to-output,

output-to-ground, and output-to-supply. When a short circuit is detected on the outputs, the part immediately

disables the output drive. This is an unlatched fault. Normal operation is restored when the fault is removed.

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