TDA8950 datasheet(8/39 Pages) NXP

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TDA8950_1

Preliminary data sheet

Rev. 01 — 9 September 2008

8 of 39

NXP Semiconductors

TDA8950

× 150 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 that typically

lies between 300 kHz and 400 kHz. Using a 2nd-order LC demodulation ﬁlter in the

application results in an analog audio signal across the loudspeaker. The carrier

frequency is determined by an external resistor ROSC, connected between pin OSC and

pin VSSA. An optimal setting for the carrier frequency is between 300 kHz and 400 kHz.

Using an external resistor of 30 k

Ω on pin OSC, the carrier frequency is set to 345 kHz.

For more details see Table 8.

If two or more class-D ampliﬁers are used in the same audio application, it is

recommended that all devices operate at the same switching frequency by using an

external clock circuit.

Due to an internal clock divider:

• The external applied clock frequency must have the double frequency of the output

PWM frequency.

• The duty cycle of the external clock is not critical for product performance.

8.3 Protections

The following protections are included in TDA8950:

• Thermal protections:

– Thermal FoldBack (TFB)

– OverTemperature Protection (OTP)

• OverCurrent Protection (OCP, diagnostic via pin PROT)

• Window Protection (WP)

• Supply voltage protections:

– UnderVoltage Protection (UVP)

– OverVoltage Protection (OVP)

– UnBalance Protection (UBP)

The reaction of the device to the different fault conditions differs per protection.

8.3.1 Thermal protection

In the TDA8950 an advanced thermal protection strategy is implemented. It consists of a

TFB function that gradually reduces the out put power within a certain temperature range.

When temperature is still rising an OTP is implemented which shuts down the device

completely.

8.3.1.1

Thermal FoldBack (TFB)

If the junction temperature Tj exceeds a deﬁned threshold value, the gain is gradually

reduced. This will result in a smaller output signal and less dissipation. Eventually the

temperature will stabilize.

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