TAS5715 datasheet(22/74 Pages) TI

22 / 74 page

TAS5715

SLOS645 – AUGUST 2010

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DETAILED DESCRIPTION

POWER SUPPLY

To facilitate system design, the TAS5715 needs only a 3.3-V supply in addition to the (typical) 18-V power-stage

supply. An internal voltage regulator provides suitable voltage levels for the gate drive 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 a few external capacitors.

In order to provide good electrical and acoustical characteristics, the PWM signal path for the output stage is

designed as identical, independent half-bridges. For this reason, each half-bridge has separate bootstrap pins

(BST_x) and power-stage supply pins (PVDD_x). The gate drive voltages (GVDD_AB and GVDD_CD) are

derived from the PVDD voltage. 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.

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 regulator output pin (GVDD_x) and the

bootstrap pin. 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. In an application with PWM

switching frequencies in the range from 352 kHz to 384 kHz, 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. 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 100-nF ceramic capacitor placed as close as possible to each supply pin.

The TAS5715 is fully protected against erroneous power-stage turnon due to parasitic gate charging.

2C CHIP SELECT/HP_SHUTDOWN

A_SEL/HP_SD is an input pin during power up. It can be pulled high or low. HIGH indicates an I2C subaddress

of 0x56, and LOW a subaddress of 0x54.

When used in headphone mode, this pin can be re-assigned as an output after reset during the initialization

sequence. Then this pin functions as headphone shutdown (active-high shutdown). A device with a headphone

should use an external pulldown, so the address is 0x54.

SINGLE-FILTER PBTL MODE

The TAS5715 supports parallel BTL (PBTL) mode with OUT_A/OUT_B (and OUT_C/OUT_D) connected before

the LC filter. In order to put the part in PBTL configuration, drive PBTL (pin 8) HIGH. This synchronizes the

turnoff of half-bridges A and B (and similarly C/D) if an overcurrent condition is detected in either half-bridge.

There is a pulldown resistor on the PBTL pin that configures the part in BTL mode if the pin is left floating.

PWM output multiplexers should be updated to set the device in PBTL mode. Output Mux Register (0x25) should

be written with a value of 0x01 10 32 45. Also, the PWM shutdown register (0x19) should be written with a value

of 0x3A.

DEVICE PROTECTION SYSTEM

Overcurrent (OC) Protection With Current Limiting

The device has independent, fast-reacting current detectors on all high-side and low-side power-stage FETs. The

detector outputs are closely monitored by two protection systems. The first protection system controls the power

stage in order to prevent the output current further increasing, i.e., it performs a cycle-by-cycle current-limiting

function, rather than prematurely shutting down during combinations of high-level music transients and extreme

speaker load impedance drops. If the high-current condition situation persists, i.e., the power stage is being

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