TDA8932B Datasheet, PDF(9/48 Page) NXP Semiconductors

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TDA8932B Datasheet, PDF (9/48 Pages) NXP Semiconductors – Class-D audio amplifier

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NXP Semiconductors

TDA8932B

Class-D audio ampliï¬er

8.4.1 Thermal Foldback (TF)

If the junction temperature of the TDA8932B exceeds the threshold level (Tj > 140 Â°C) the

gain of the ampliï¬er is decreased gradually to a level where the combination of dissipation

(P) and the thermal resistance from junction to ambient [Rth(j-a)] results in a junction

temperature around the threshold level.

This means that the device will not completely switch off, but remains operational at lower

output power levels. Especially with music output signals this feature enables high peak

output power while still operating without any external heat sink other than the

printed-circuit board area.

If the junction temperature still increases due to external causes, the OTP shuts down the

ampliï¬er completely.

8.4.2 OverTemperature Protection (OTP)

If the junction temperature Tj > 155 Â°C, then the power stage will shut down immediately.

8.4.3 OverCurrent Protection (OCP)

When the loudspeaker terminals are short-circuited or if one of the demodulated outputs

of the ampliï¬er is short-circuited to one of the supply lines, this will be detected by the

OCP.

If the output current exceeds the maximum output current (IO(ocp) > 4 A), this current will

be limited by the ampliï¬er to 4 A while the ampliï¬er outputs remain switching (the ampliï¬er

is NOT shutdown completely). This is called current limiting.

The ampliï¬er can distinguish between an impedance drop of the loudspeaker and a

low-ohmic short-circuit across the load or to one of the supply lines. This impedance

threshold depends on the supply voltage used:

â¢ In case of a short-circuit across the load, the audio ampliï¬er is switched off completely

and after approximately 100 ms it will try to restart again. If the short-circuit condition

is still present after this time, this cycle will be repeated. The average dissipation will

be low because of this low duty cycle.

â¢ In case of a short to one of the supply lines, this will trigger the OCP and the ampliï¬er

will be shut down. During restart the window protection will be activated. As a result

the ampliï¬er will not start until 100 ms after the short to the supply lines is removed.

â¢ In case of impedance drop (e.g. due to dynamic behavior of the loudspeaker) the

same protection will be activated. The maximum output current is again limited to 4 A,

but the ampliï¬er will NOT switch off completely (thus preventing audio holes from

occurring). The result will be a clipping output signal without any artifacts.

8.4.4 Window Protection (WP)

The WP checks the PWM output voltage before switching from Sleep mode to Mute mode

(outputs switching) and is activated:

â¢ During the start-up sequence, when pin POWERUP is switched from Sleep mode to

Mute mode. In the event of a short-circuit at one of the output terminals to VDDP1,

VSSP1, VDDP2 or VSSP2 the start-up procedure is interrupted and the TDA8932B waits

for open-circuit outputs. Because the check is done before enabling the power stages,

no large currents will ï¬ow in the event of a short-circuit.

TDA8932B_4

Product data sheet

Rev. 04 â 18 December 2008

9 of 48

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