TDA8950 datasheet(9/39 Pages) NXP

9 / 39 page

TDA8950_1

Preliminary data sheet

Rev. 01 — 9 September 2008

9 of 39

NXP Semiconductors

TDA8950

× 150 W class-D power ampliﬁer

TFB is speciﬁed at the temperature value Tact(th_fold) where the closed loop voltage gain is

reduced with 6 dB. The range of the TFB is:

Tact(th_fold) − 5 °C < Tact(th_fold) < Tact(th_prot).

For the TDA8950 the value of Tact(th_fold) is about +153 °C. For more details see: Table 7.

8.3.1.2

OverTemperature Protection (OTP)

If, despite the TFB function, the junction temperature Tj of the TDA8950 continues rising

and exceeds the threshold Tact(th_prot) the ampliﬁer will shutdown immediately. The

ampliﬁer resumes switching approximately 100 ms after the temperature drops below

Tact(th_prot).

In Figure 6 the thermal behavior is visualized.

8.3.2 OverCurrent Protection (OCP)

If a short-circuit is applied to one of the demodulated outputs of the ampliﬁer, the OCP will

detect this. If the output current exceeds the maximum of 9.2 A, it is automatically limited

to its maximum value by the OCP protection circuit. The ampliﬁer outputs remain

switching (the ampliﬁer is NOT shut-down completely). If the active current limiting

continues longer than time

τ, the TDA8950 shuts down. Activation of current limiting and

the triggering of the OCP are observed at pin PROT.

The ampliﬁer can distinguish between an impedance drop of the loudspeaker and a

low-ohmic short-circuit across the load. In the TDA8950 the impedance threshold (Zth)

depends on the supply voltage used.

When a short-circuit is made across the load, causing the impedance to drop below the

threshold level (<Zth), the ampliﬁer is switched off completely and, after a time of 100 ms,

it will try to restart. If the short-circuit condition is still present after this time, the cycle will

be repeated. The average dissipation will be low because of this low duty cycle.

(1) Duty cycle of PWM output modulated according audio input signal.

(2) Duty cycle of PWM output reduced due to TFB.

(3) Ampliﬁer is switched off due to OTP.

Fig 6.

Behavior of TFB and OTP

001aah656

(Tact(th_fold) − 5°C)

Tact(th_fold)

Tj (°C)

Tact(th_prot)

Gain

(dB)

30 dB

24 dB

0 dB

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