Pulse-Width Modulation Frequency; Protection; Thermal Protection; Thermal Foldback (Tfb) - Philips TDA8950 Product Data Sheet

NXP Semiconductors

8.2 Pulse-width modulation frequency

8.3 Protection

8.3.1 Thermal protection

8.3.1.1 Thermal FoldBack (TFB)

TDA8950_2
Product data sheet
The amplifier output signal is a PWM signal with a typical carrier frequency of between
250 kHz and 450 kHz. A 2nd-order LC demodulation filter on the output is used to convert
the PWM signal into an analog audio signal. The carrier frequency is determined by an
external resistor, R
OSC
frequency setting is between 250 kHz and 450 kHz.
The carrier frequency is set to 345 kHz by connecting an external 30 k resistor between
pins OSC and VSSA. See
If two or more Class D amplifiers are used in the same audio application, it is
recommended that an external clock circuit be used with all devices (see
This will ensure that they operate at the same switching frequency, thus avoiding beat
tones (if the switching frequencies are different, audible interference known as 'beat tones'
can be generated)
The following protection circuits are incorporated into the TDA8950:
•
Thermal protection:
– Thermal FoldBack (TFB)
– OverTemperature Protection (OTP)
•
OverCurrent Protection (OCP)
•
Window Protection (WP)
•
Supply voltage protection:
– UnderVoltage Protection (UVP)
– OverVoltage Protection (OVP)
– UnBalance Protection (UBP)
How the device reacts to a fault conditions depends on which protection circuit has been
activated.
The TDA8950 employes an advanced thermal protection strategy. A TFB function
gradually reduces the output power within a defined temperature range. If the temperature
continues to rise, OTP is activated to shut down the device completely.
If the junction temperature (T
is gradually reduced. This reduces the output signal amplitude and the power dissipation,
eventually stabilizing the temperature.
TFB is specified at the thermal foldback activation temperature T
closed-loop voltage gain is reduced by 6 dB. The TFB range is:
T 5 C < T
act(th_fold) act(th_fold)
The value of T
act(th_fold)
details.
, connected between pins OSC and VSSA. The optimal carrier
Table 9 for more details.
) exceeds the thermal foldback activation threshold, the gain
j
< T
act(th_prot)
for the TDA8950 is approximately 153 C; see
Rev. 02 — 11 June 2009
TDA8950
2 150 W class-D power amplifier
Section
where the
act(th_fold)
Table 8
© NXP B.V. 2009. All rights reserved.
13.4).
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