CS4525 datasheet(57/98 Pages) CIRRUS

57 / 98 page

DS726PP1

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 page 20.

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. Figure 18

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 Table 16 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

tdelay

Foldback Attack Delay

Approximately 2 sec.

tdelay

When the junction temperature crosses the thermal warning threshold, the foldback attack delay timer is started.

When the foldback attack delay timer reaches tdelay 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.

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

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