TDA8954_1 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 01 — 24 December 2009 8 of 46
NXP Semiconductors
TDA8954
2 × 210 W class-D power amplifier
8.2 Diagnostics
The TDA8954 provides two diagnostic signals on pins DIAG1 and DIAG2. Both are
open-drain outputs that can be pulled up via a resistor (10 kΩ recommended) to a
maximum of 5
V relative to the GND pin. The maximum input current on these pins is
1
mA.
Pin DIAG1 provides a TFB warning signal. Pin DIAG2 can be used to monitor the OCP
status and the protection status (whether one of the protection circuits has switched off the
amplifier).
Details of the timing of these signals can be found in Section 8.4.1.1 and Section 8.4.2;
see also Table 5.
8.3 Pulse-width modulation frequency
The amplifier output signal is a PWM signal with a typical carrier frequency of between
250
kHz and 450 kHz. A second-order LC demodulation filter on the output converts the
PWM signal into an analog audio signal. The carrier frequency, f
OSC
, is determined by an
external resistor, R
OSC
, connected between pins OSC and OSCREF. The optimal carrier
frequency setting is between 250
kHz and 450 kHz.
The carrier frequency is set to 335 kHz by connecting an external 30 kΩ resistor between
pins OSC and OSCREF (see
Figure 6).
If two or more Class D amplifiers are used in the same audio application, an external clock
circuit must be used to synchronize all amplifiers (see
Section 14.4). 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).
Fig 6. Carrier frequency as a function of R
OSC
R
OSC
(kΩ)
20 454030 3525
010aaa596
300
400
500
f
OSC
(kHz)
200