8.2.2.6 BSN and BSP Capacitors

The full 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 0.22-μF ceramic capacitor, rated for at least 25 V, must be

connected from each output to its corresponding bootstrap input. Specifically, one 0.22-μF capacitor must be

connected from OUTPx to BSPx, and one 0.22-μF capacitor must be connected from OUTNx to BSNx. (See the

application circuit diagram in Figure 8-1.)

The bootstrap capacitors connected between the BSxx 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.

8.2.2.7 Differential Inputs

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

use the TPA3139D2 device 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 TPA3139D2 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 3 ms or less if possible. This is to

allow the input dc blocking capacitors to become completely charged during the 50-ms power-up time. If the

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

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

8.2.2.8 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.

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TPA3139D2

SLOS810A – OCTOBER 2019 – REVISED AUGUST 2020

Copyright © 2020 Texas Instruments Incorporated

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