Thermal protection

TDA7564B

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6

Thermal protection

Thermal protection is implemented through thermal foldback (Figure 29).

Thermal foldback begins limiting the audio input to the amplifier stage as the junction

temperatures rise above the normal operating range. This effectively limits the output power

capability of the device thus reducing the temperature to acceptable levels without totally

interrupting the operation of the device.

The output power will decrease to the point at which thermal equilibrium is reached.

Thermal equilibrium will be reached when the reduction in output power reduces the

dissipated power such that the die temperature falls below the thermal foldback threshold.

Should the device cool, the audio level will increase until a new thermal equilibrium is

reached or the amplifier reaches full power. Thermal foldback will reduce the audio output

level in a linear manner.

Figure 29. Thermal foldback diagram

6.1

A correct turn on/off sequence respectful of the diagnostic timings and producing no audible

noises could be as follows (after battery connection):

Turn-on: (stand-by out + diag enable) --- 500 ms (min.) --- muting out

Turn-off: muting in --- 20 ms --- (diag disable + stand-by in)

disappear).

Tj ( °C)

TH. SH.

START

TH. SH.

END

Vout

TH. WARN.

ON

Tj ( °C)

Vout

Tj ( °C)

SD

(with same input

signal)

CD out

TH. WARN.

ON

TH. WARN.

ON

125°

140°

155°

> T