TAS5142 datasheet(21/30 Pages) TI2

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Use

TAS5142

High-Modulation-Index

ERROR REPORTING

Overcurrent

(OC)

Protection

With

Current

DEVICE PROTECTION SYSTEM

TAS5142

SLES126B – DECEMBER 2004 – REVISED MAY 2005

Characteristics section of this data sheet). Although

temperature has dropped or the supply voltage has

not specifically required, it is a good practice to hold

increased. For highest possible reliability, recovering

RESET_AB and RESET_CD low during power down,

from an overload fault requires external reset of the

thus preventing audible artifacts including pops or

device (see the Device Reset section of this data

clicks.

sheet) no sooner than 1 second after the shutdown.

When the TAS5142 is being used with TI PWM

modulators

such

the

TAS5508,

special

Capable Systems

attention to the state of RESET_AB and RESET_CD

This device requires at least 50 ns of low time on the

is required, provided that the chipset is configured as

output per 384-kHz PWM frame rate in order to keep

recommended.

the bootstrap capacitors charged. As an example, if

the modulation index is set to 99.2% in the TAS5508,

this setting allows PWM pulse durations down to 20

The

and

OTW

pins

are

both

active-low,

ns. This signal, which does not meet the 50-ns

open-drain

outputs.

Their

function

for

requirement, is sent to the PWM_X pin and this

protection-mode signaling to a PWM controller or

low-state pulse time does not allow the bootstrap

other system-control device.

capacitor to stay charged. In this situation, the low

voltage across the bootstrap capacitor can cause a

Any fault resulting in device shutdown is signaled by

failure of the high-side MOSFET transistor, especially

the SD pin going low. Likewise, OTW goes low when

when driving a low-impedance load. The TAS5142

the device junction temperature exceeds 125

°C (see

device requires limiting the TAS5508 modulation

the following table).

index to 96.1% to keep the bootstrap capacitor

OTW

DESCRIPTION

charged under all signals and loads.

Overtemperature (OTE) or overload (OLP) or

Therefore, TI strongly recommends using a TI PWM

undervoltage (UVP)

processor, such as TAS5508 or TAS5086, with the

Overload (OLP) or undervoltage (UVP)

modulation index set at 96.1% to interface with

Junction temperature higher than 125°C

TAS5142.

(overtemperature warning)

Junction temperature lower than 125°C and no

OLP or UVP faults (normal operation)

Limiting and Overload Detection

Note that asserting either RESET_AB or RESET_CD

The device has independent, fast-reacting current

low forces the SD signal high, independent of faults

detectors with programmable trip threshold (OC

being present. TI recommends monitoring the OTW

threshold) on all high-side and low-side power-stage

signal

using

the

system

microcontroller

and

FETs. See the following table for OC-adjust resistor

responding to an overtemperature warning signal by,

values. The detector outputs are closely monitored by

e.g., turning down the volume to prevent further

two protection systems. The first protection system

heating of the device resulting in device shutdown

controls the power stage in order to prevent the

(OTE).

output current from further increasing, i.e., it performs

a current-limiting function rather than prematurely

To reduce external component count, an internal

shutting down during combinations of high-level

pullup resistor to 3.3 V is provided on both SD and

music

transients

and

extreme

speaker

load

OTW outputs. Level compliance for 5-V logic can be

impedance

drops.

the

high-current

situation

obtained by adding external pullup resistors to 5 V

persists, i.e., the power stage is being overloaded, a

(see the Electrical Characteristics section of this data

second

protection

system

triggers

latching

sheet for further specifications).

shutdown, resulting in the power stage being set in

the high-impedance (Hi-Z) state. Current limiting and

overload protection are independent for half-bridges

The TAS5142 contains advanced protection circuitry

A and B and, respectively, C and D. That is, if the

carefully designed to facilitate system integration and

bridge-tied load between half-bridges A and B causes

ease of use, as well as to safeguard the device from

an overload fault, only half-bridges A and B are shut

permanent failure due to a wide range of fault

down.

conditions

such

short

circuits,

overload,

•

For the lowest-cost bill of materials in terms of

overtemperature, and undervoltage. The TAS5142

component selection, the OC threshold measure

responds to a fault by immediately setting the power

should be limited, considering the power output

stage in a high-impedance (Hi-Z) state and asserting

requirement

and

minimum

load

impedance.

the SD pin low. In situations other than overload, the

Higher-impedance loads require a lower OC

device

automatically

recovers

when

the

fault

threshold.

condition has been removed, i.e.,

the

junction

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