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| TDA8920C Datasheet, PDF (9/40 Pages) NXP Semiconductors – 2 X110 W class-D power amplifier | |||
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NXP Semiconductors
TDA8920C
2 à 110 W class-D power ampliï¬er
TFB is speciï¬ed at the thermal foldback activation temperature Tact(th_fold) where the
closed-loop voltage gain is reduced by 6 dB. The TFB range is:
Tact(th_fold) â 5 °C < Tact(th_fold) < Tact(th_prot)
The value of Tact(th_fold) for the TDA8920C is approximately 153 °C; see Table 7 for more
details.
8.3.1.2 OverTemperature Protection (OTP)
If despite the TFB function, the junction temperature (Tj) of the TDA8920C continues to
rise exceeding the thermal protection activation temperature Tact(th_prot), the ampliï¬er
shuts down immediately. The ampliï¬er resumes switching approximately 100 ms after the
temperature drops below Tact(th_prot).
The thermal behavior is illustrated in Figure 6.
Gain
(dB)
30 dB
24 dB
0 dB
(Tact(th_fold) â 5°C)
Tact(th_prot)
Tact(th_fold)
Tj (°C)
1
2
3
001aah656
(1) Duty cycle of PWM output modulated according to the audio input signal.
(2) Duty cycle of PWM output reduced due to TFB.
(3) Ampliï¬er is switched off due to OTP.
Fig 6. Behavior of TFB and OTP
8.3.2 OverCurrent Protection (OCP)
OverCurrent Protection (OCP) will detect a short-circuit applied to any of the demodulated
outputs of the ampliï¬er. If the output current exceeds the 9.2 A maximum, it is
automatically limited to its maximum value by the OCP protection circuit, the ampliï¬er is
NOT shut down completely, and the ampliï¬er outputs continue switching. If the active
current limiting continues longer than time (Ï), the TDA8920C shuts down. Activation of
current limiting and the triggering of OCP are output at pin PROT.
OCP can distinguish between a loudspeaker impedance drop and a low-ohmic
short-circuit across the load. In the TDA8920C, the impedance threshold (Zth) depends on
the supply voltage used.
If a short-circuit occurs across the load causing the impedance to drop below the
threshold level (< Zth), the ampliï¬er switches off completely. After 100 ms, it tries to restart.
If the short-circuit condition is still present, the cycle is repeated. The average power
dissipation will be low because of the low duty cycle.
TDA8920C_1
Preliminary data sheet
Rev. 01 â 29 September 2008
© NXP B.V. 2008. All rights reserved.
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