CS4525 datasheet(40/98 Pages) CIRRUS

40 / 98 page

DS726PP1

CS4525

6.1.4.12 Thermal Foldback

The CS4525 implements comprehensive thermal foldback features to guard against damaging thermal

overload conditions. Thermal foldback is similar to the thermal limiting described on page 39 in that both

features attenuate the output signal in response to thermal warnings conditions; however, thermal fold-

back will attenuate as a function of how long thermal warning has been active whereas thermal limiter

always limits by a constant amount. Also, the thermal foldback feature will deactivate once the thermal

warning condition ceases while the thermal limiter will remain active once triggered until the RST pin is

driven low.

The thermal foldback algorithm 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 warn-

ing 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

Threshold

tdelay

Foldback Attack Delay

AttackDly[1:0]

tdelay

The junction temperature is checked once again after the next foldback attack timer timeout. If it 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. Setting the LockAdj bit will prevent the device from removing the applied attenuation when the thermal

overload condition has cleared.

If the junction temperature crosses the thermal warning threshold again, the foldback algorithm will once again enter

step 1.

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 the junction

temperature 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.

Figure 18. Foldback Process

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