TDA7564B Datasheet, PDF (20/34 Pages) STMicroelectronics – 4 x 50W multifunction quad power amplifier with built-in diagnostics features

Thermal protection
6
Thermal protection
TDA7564B
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.
Three Thermal warning are available through the I²C bus data.
Figure 29. Thermal foldback diagram
Vout
TH. WARN. TH. WARN. TH. WARN.
ON
ON
ON
Vout
125°
140°
155°
TH. SH.
START
TH. SH. _{Tj ( °C)}
END
CD out
< TSD
> TSD (with same input
signal)
Tj ( °C)
6.1
20/34
Tj ( °C)
I²C programming/reading sequences
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)
Car Radio Installation: diag enable (write) --- 200 ms --- I²C read (repeat until All faults
disappear).
AC test: feed h.f. tone -- AC diag enable (write) --- wait > 3 cycles --- I²C read
(repeat I²C reading until tweeter-off message disappears).
Offset test: Device in play (no signal) -- offset enable - 30ms - I²C reading
(repeat I²C reading until high-offset message disappears).