TDF8599B datasheet(14/54 Pages) NXP

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NXP Semiconductors

TDF8599B

I2C-bus controlled dual channel 43 W/2 Ohm, single channel 85 W/1 Ohm class-D power amplifier with

load diagnostics

TDF8599B

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 2 — 23 August 2016

14 / 54

8.5 Protection

The TDF8599B includes a range of built-in protection functions. How the TDF8599B

manages the various possible fault conditions for each protection is described in the

following sections:

Table 9. Overview of protection types

Protection type

Reference

Thermal foldback

Section 8.5.1

Overtemperature

Section 8.5.2

Overcurrent

Section 8.5.3

Window

Section 8.5.4

DC Offset

Section 8.5.5

Undervoltage

Section 8.5.6

Overvoltage

Section 8.5.6

8.5.1 Thermal foldback

Thermal Foldback Protection (TFP) is activated when the average junction temperature

exceeds the threshold level (145 °C). TFP decreases amplifier gain such that the

combination of power dissipation and Rth(j-a) create a junction temperature around the

threshold level. The device will not completely switch off but remains operational at the

lower output power levels. If the average junction temperature continues to increase,

a second built-in temperature protection threshold level shuts down the amplifier

completely.

8.5.2 Overtemperature protection

If the average junction temperature Tj > 160 °C, OverTemperature Protection (OTP) is

activated and the power stage shuts down immediately.

8.5.3 Overcurrent protection

OverCurrent Protection (OCP) is activated when the output current exceeds the

maximum output current of 8 A. OCP regulates the output voltage such that the

maximum output current is limited to 8 A. The amplifier outputs keep switching and the

amplifier is NOT shutdown completely. This is called current limiting.

OCP also detects when the loudspeaker terminals are short circuited or one of the

amplifier’s demodulated outputs is short circuited to one of the supply lines. In either

case, the shorted channel(s) are switched off.

The amplifier can distinguish between loudspeaker impedance drops and a low-ohmic

short across the load or one of the supply lines. This impedance threshold depends on

the supply voltage used. When a short is made across the load causing the impedance to

drop below the threshold level, the shorted channel(s) are switched off. They try to restart

every 50 ms. If the short circuit condition is still present after 50 ms, the cycle repeats.

The average power dissipation will be low because of this reduced duty cycle.

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