TDA8924 Datasheet, PDF (7/35 Pages) NXP Semiconductors – 2 x 120 W class-D power amplifier

Philips Semiconductors
2 × 120 W class-D power amplifier
Objective specification
TDA8924
handbook, full pagewidth
When switching from standby
to mute, there is a delay of
100 ms before the output
starts switching. The audio
signal is available after V_mode
has been set to operating, but
not earlier than 150 ms after
switching to mute.
Vmode
4V
2V
standby
0 V (SGND)
mute
100 ms
>50 ms
audio
switching
operating
time
When switching from standby
to operating, there is a first
delay of 100 ms before the
outputs starts switching. The
audio signal is available after
a second delay of 50 ms.
Vmode
4V
audio
switching
operating
standby
0 V (SGND)
100 ms
50 ms
Fig.4 Timing on mode select input.
time
MBL465
8.2 Pulse width modulation frequency
The output signal of the amplifier is a PWM signal with a
carrier frequency of approximately 350 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
R_OSC connected between pin OSC and V_SSA. With the
resistor value given in the schematic diagram of the
reference design, the carrier frequency is typical 350 kHz.
The carrier frequency can be calculated using the
following equation: f_osc = ^9---R--×--_O---1-_S---0_C---⁹- Hz
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.
This can be realized by connecting all OSC pins together
and feed them from an external central oscillator. Using an
external oscillator it is necessary to force pin OSC to a
DC-level above SGND for switching from internal to an
external oscillator. In this case the internal oscillator is
disabled and the PWM will be switched to the external
frequency. The frequency range of the external oscillator
must be in the range as specified in the switching
characteristics; see Chapter 13.
2003 Jul 28
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