TAS5611A

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SLAS709 – JUNE 2010

THEORY OF OPERATION

POWER SUPPLIES

To facilitate system design, the TAS5611A needs only a 12V supply in addition to the (typical) 32.5V

power-stage supply. An internal voltage regulator provides suitable voltage levels for the digital and low-voltage

analog circuitry. Additionally, all circuitry requiring a floating voltage supply, e.g., the high-side gate drive, is

accommodated by built-in bootstrap circuitry requiring only an external capacitor for each half-bridge.

To provide outstanding electrical and acoustical characteristics, the PWM signal path including gate drive and

output stage is designed as identical, independent half-bridges. For this reason, each half-bridge has separate

gate drive supply (GVDD_X), bootstrap pins (BST_X), and power-stage supply pins (PVDD_X). Furthermore, an

additional pin (VDD) is provided as supply for all common circuits. Although supplied from the same 12V source,

it is highly recommended to separate GVDD_A, GVDD_B, GVDD_C, GVDD_D, and VDD on the printed-circuit

board (PCB) by RC filters (see application diagram for details). 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, inductance between the power supply pins and decoupling capacitors

must be avoided. (See reference board documentation for additional information.)

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_X) and the

bootstrap pin. When the powerstage 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. In an application with PWM

switching frequencies in the range from 300kHz to 400kHz, it is recommended to use 33nF ceramic capacitors,

size 0603 or 0805, for the bootstrap supply. These 33nF 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. As indicated, each half-bridge has independent power-stage supply pins (PVDD_X). For

optimal electrical performance, EMI compliance, and system reliability, it is important that each PVDD_X pin is

decoupled with a 2mF ceramic capacitor placed as close as possible to each supply pin. It is recommended to

follow the PCB layout of the TAS5611A reference design. For additional information on recommended power

supply and required components, see the application diagrams in this data sheet.

The 12V supply should be from a low-noise, low-output impedance voltage regulator. Likewise, the 32.5V

power-stage supply is assumed to have low output impedance and low noise. The power-supply sequence is not

critical as facilitated by the internal power-on-reset circuit. Moreover, the TAS5611A is fully protected against

erroneous power-stage turn on due to parasitic gate charging. Thus, voltage-supply ramp rates (dV/dt) are

non-critical within the specified range (see the Recommended Operating Conditions table of this data sheet).

SYSTEM POWER-UP/POWER-DOWN SEQUENCE

Powering Up

The TAS5611A does not require a power-up sequence. The outputs of the H-bridges remain in a

high-impedance state until the gate-drive supply voltage (GVDD_X) and VDD voltage are above the undervoltage

protection (UVP) voltage threshold (see the Electrical Characteristics table of this data sheet). Although not

specifically required, it is recommended to hold RESET in a low state while powering up the device. This allows

an internal circuit to charge the external bootstrap capacitors by enabling a weak pulldown of the half-bridge

output.

Powering Down

The TAS5611A does not require a power-down sequence. The device remains fully operational as long as the

gate-drive supply (GVDD_X) voltage and VDD voltage are above the undervoltage protection (UVP) voltage

threshold (see the Electrical Characteristics table of this data sheet). Although not specifically required, it is a

good practice to hold RESET low during power down, thus preventing audible artifacts including pops or clicks.

Copyright © 2010, Texas Instruments Incorporated

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