TDF8599BTH datasheet(15/54 Pages) NXP

15 / 54 page

TDF8599B_1

Product data sheet

Rev. 01 — 29 July 2009

15 of 54

NXP Semiconductors

TDF8599B

I2C-bus controlled dual channel class-D power ampliﬁer

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.

When a channel is switched off due to a short circuit on one of the supply lines, Window

Protection (WP) is activated. WP ensures the ampliﬁer does not start-up after 50 ms until

the supply line short circuit is removed.

8.5.4 Window protection

Window Protection (WP) checks the PWM output voltage before switching from Standby

mode to Mute mode (with both outputs switching) and is activated as follows:

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

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