DS726PP2
57
CS4525
6.2.6
Thermal Foldback
In hardware mode, the CS4525 implements a thermal foldback feature to guard against damaging thermal
overload conditions. The thermal foldback feature begins limiting the volume of the digital audio input to
the amplifier stage as the junction temperatures rise above the maximum safe operating range specified
by the thermal warning trigger point listed in the
PWM Power Output Characteristics
table on
This effectively limits the output power capability of the device, thereby allowing the temperature to reduce
to acceptable levels without fully interrupting operation. As the device cools, the applied attenuation is
gradually released until a new thermal equilibrium is reached or all applied attenuation has been released
thereby allowing the device to again achieve its full output power capability.
Attenuation applied due to thermal foldback reduces the audio output level in a linear manner.
below demonstrates the foldback process.
Thermal warning conditions will only affect the foldback algorithm and cause attenuation to be applied if
enabled by the EN_TFB pin as shown in
below.
EN_TFB
Selected Thermal Foldback Enable State
Low
Thermal foldback disabled.
High
Thermal foldback enabled.
Table 16. Thermal Foldback Enable Selection
Thermal Warning
Threshold
t
delay
1
2
2
2
2
3
1
Foldback Attack Delay
Approximately 2 sec.
t
delay
t
delay
t
delay
t
delay
1
When the junction temperature crosses the thermal warning threshold, the foldback attack delay timer is started.
2
When the foldback attack delay timer reaches t
delay
seconds, the junction temperature is checked. If it is above the
thermal warning threshold, the output volume level is lowered by 0.5 dB and the foldback attack timer is restarted.
The junction temperature is checked after each foldback attack timer timeout, and if necessary, the output volume
level is lowered accordingly.
If the junction temperature is found to be below the thermal warning threshold, the foldback attack timer is
restarted once again, but the output volume level is not altered. The foldback algorithm then proceeds to step 3.
3
The junction temperature is checked once again after the next foldback attack timer timeout. If is has remained
below the thermal warning threshold since the last check, the device will begin to release any attenuation applied
as a result of the foldback event.
If the junction temperature crosses the thermal warning threshold again, the foldback algorithm will once again
enter step 1.
Figure 25. Foldback Process
