Datasheet

TPA3112D1

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SLOS654C –SEPTEMBER 2009–REVISED JULY 2012

Optimum decoupling is achieved by using a network of capacitors of different types that target specific types of

noise on the power supply leads. For higher frequency transients due to parasitic circuit elements such as bond

wire and copper trace inductances as well as lead frame capacitance, a good quality low equivalent-series-

resistance (ESR) ceramic capacitor of value between 220 pF and 1000 pF works well. This capacitor should be

placed as close to the device PVCC pins and system ground (either PGND pins or PowerPad) as possible. For

mid-frequency noise due to filter resonances or PWM switching transients as well as digital hash on the line,

another good quality capacitor typically 0.1 mF to 1 μF placed as close as possible to the device PVCC leads

works best For filtering lower frequency noise signals, a larger aluminum electrolytic capacitor of 220 mF or

greater placed near the audio power amplifier is recommended. The 220 mF capacitor also serves as a 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. Also, a small decoupling resistor between

AVCC and PVCC can be used to keep high frequency class D noise from entering the linear input amplifiers.

BSN and BSP CAPACITORS

The full H-bridge output stage uses only NMOS transistors. Therefore, they require bootstrap capacitors for the

high side of each output to turn on correctly. A 470-nF ceramic capacitor, rated for at least 16 V, must be

connected from each output to its corresponding bootstrap input. Specifically, one 470-nF capacitor must be

connected from OUTP to BSP, and one 470-nF capacitor must be connected from OUTN to BSN. (See the

application circuit diagram in Figure 1.)

The bootstrap capacitors connected between the BSx pins and corresponding output 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.

DIFFERENTIAL INPUTS

The differential input stage of the amplifier cancels any noise that appears on both input lines of the channel. To

use the TPA3112D1 with a differential source, connect the positive lead of the audio source to the INP input and

the negative lead from the audio source to the INN input. To use the TPA3112D1 with a single-ended source, ac

ground the INP or INN input through a capacitor equal in value to the input capacitor on INN or INP and apply

the audio source to either input. In a single-ended input application, the unused input should be ac grounded at

the audio source instead of at the device input for best noise performance. For good transient performance, the

impedance seen at each of the two differential inputs should be the same.

The impedance seen at the inputs should be limited to an RC time constant of 1 ms or less if possible. This is to

allow the input dc blocking capacitors to become completely charged during the 14 msec power-up time. If the

input capacitors are not allowed to completely charge, there will be some additional sensitivity to component

matching which can result in pop if the input components are not well matched.

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.

Product Folder Link(s): TPA3112D1