TDA8920B
Philips Semiconductors
2 × 100 W class-D power amplifier
8.2 Pulse width modulation frequency
The output signal of the amplifier is a PWM signal with a carrier frequency of
approximately 317 kHz. Using a 2nd-order LC demodulation filter in the application results
in an analog audio signal across the loudspeaker. This switching frequency is fixed by an
external resistor ROSC connected between pin OSC and VSSA. An optimal setting for the
carrier frequency is between 300 kHz and 350 kHz.
Using an external resistor of 30 kΩ on the OSC pin, the carrier frequency is set to
317 kHz.
If two or more class-D amplifiers are used in the same audio application, it is advisable to
have all devices operating at the same switching frequency by using an external clock
circuit.
8.3 Protections
The following protections are included in TDA8920B:
• OverTemperature Protection (OTP)
• OverCurrent Protection (OCP)
• Window Protection (WP)
• Supply voltage protections:
– UnderVoltage Protection (UVP)
– OverVoltage Protection (OVP)
– UnBalance Protection (UBP).
The reaction of the device on the different fault conditions differs per protection:
8.3.1 OverTemperature Protection (OTP)
If the junction temperature Tj > 150 °C, then the power stage will shut-down immediately.
The power stage will start switching again if the temperature drops to approximately
130 °C, thus there is a hysteresis of approximately 20 °C.
8.3.2 OverCurrent Protection (OCP)
When the loudspeaker terminals are short-circuited or if one of the demodulated outputs
of the amplifier is short-circuited to one of the supply lines, this will be detected by the
OverCurrent Protection (OCP). If the output current exceeds the maximum output current
of 8 A, this current will be limited by the amplifier to 8 A while the amplifier outputs remain
switching (the amplifier is NOT shut-down completely).
The amplifier can distinguish between an impedance drop of the loudspeaker and
low-ohmic short across the load. In the TDA8920B this impedance threshold (Zth)
depends on the supply voltage used.
When a short is made across the load causing the impedance to drop below the threshold
level (< Zth) then the amplifier is switched off completely and after a time of 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.
9397 750 13356
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Preliminary data sheet
Rev. 01 — 1 October 2004
8 of 34
NXP [ NXP ]
