9.1 Overview

TPA3221 is designed as a feature-enhanced cost efficient high power Class-D audio amplifier. It has built-in advanced protection circuitry to ensure maximum product robustness as well as a flexible feature set including built in LDO for easy supply of low voltage circuitry, selectable gain, switching frequency, master/slave synchronization of multiple devices, selectable PWM modulation scheme, mute function, temperature and clipping status signals. TPA3221 has a bandwidth up to 100 kHz and low output noise designed for high resolution audio applications and accepts both differential and single ended analog audio inputs at levels from 1 V_RMS to 2 V_RMS. With its closed loop operation TPA3221 is designed for high audio performance with a system power supply between 7 V and 30 V.

To facilitate system design, the TPA3221 needs only a (typical) 30 V power stage supply. The TPA3221 has an internal voltage regulator supplied from the VDD pin for the analog and digital system blocks and the output stage gate drive respectively. The VDD pin can be connected directly to PVDD in case of only this power supply rail being available.

To reduce device power losses an external 5 V supply can be used for the AVDD and VDD supply pins. The internal voltage regulator connected to the VDD pin is automatically turned off if an external 5 V supply is used for this pin. Although supplied from the same 5 V source, separating AVDD and VDD on the printed-circuit board (PCB) by RC filters (see application diagram for details) is recommended. These RC filters provide the recommended high-frequency isolation. Special attention should be paid to placing all decoupling capacitors as close to their associated pins as possible. In general, the physical loop with the power supply pins, decoupling capacitors and GND return path to the device pins must be kept as short as possible and with as little area as possible to minimize induction (see Layout Examples for additional information).

The floating supplies for the output stage high side gate drives are supplied by built-in bootstrap circuitry requiring only an external capacitor for each half-bridge.

For a properly functioning bootstrap circuit, a small ceramic capacitor must be connected from each bootstrap pin (BST_X) to the power-stage output pin (OUT_X). When the power-stage output is low, the bootstrap capacitor is charged through an internal diode connected between the gate-drive power-supply pin (GVDD) and the bootstrap pins. When the power-stage output is high, the bootstrap capacitor potential is shifted above the output potential and thus provides a suitable voltage supply for the high-side gate driver. It is recommended to use 33 nF ceramic capacitors, size 0603 or 0805, for the bootstrap supply. These 33 nF capacitors ensure sufficient energy storage, even during minimal PWM duty cycles, to keep the high-side power stage FET (LDMOS) fully turned on during the remaining part of the PWM cycle.

Special attention should be paid to the power stage power supply; this includes component selection, PCB placement, and routing.

For optimal electrical performance, EMI compliance, and system reliability, it is important that each PVDD_X node is decoupled with 1 μF ceramic capacitors placed as close as possible to the PVDD supply pins. It is recommended to follow the PCB layout of the TPA3221 reference design. For additional information on recommended power supply and required components, see the application diagrams in this data sheet.

If using external power supply for the AVDD and VDD internal regulators, this supply should be from a low-noise, low-output-impedance voltage regulator. Likewise, the 30 V power stage supply is assumed to have low output impedance throughout the entire audio band, and low noise. The power supply sequence is not critical as facilitated by the internal power-on-reset circuit, but it is recommended to release RESET after the power supply is settled for minimum turn on audible artefacts. Moreover, the TPA3221 is fully protected against erroneous power-stage turn on due to parasitic gate charging. Thus, voltage-supply ramp rates (dV/dt) are noncritical within the specified range (see the Recommended Operating Conditions table of this data sheet).