For master mode to operate correctly then resistor ROSC must be less than 60 kΩ as given below in Table 8. How

to set up SYNCLK.

5.5.2

Slave mode (external clock)

In order to accept an external clock input the pin ROSC must be left open, that is, floating. This forces pin

SYNCLK to be internally configured as an input as given in Table 8. How to set up SYNCLK.

The output switching frequency of the slave devices is:

fSW = fSYNCLK / 2

Table 8. How to set up SYNCLK

Mode

ROSC

SYNCLK

Master

ROSC < 60 kΩ

Output

Slave

Floating (not connected)

Input

Figure 24. Master and slave connection

SYNCLK

ROSC

Rosc

Cosc

ROSC

SYNCLK

39 k Ω

100 nF

Output

Inpu t

e

v

a

l

S

r

e

t

s

a

M

TDA7498L

TDA7498L

5.6

Output low-pass filter

To avoid EMI problems, it may be necessary to use a low-pass filter before the speaker. The cutoff frequency

should be larger than 22 kHz and much lower than the output switching frequency. It is necessary to choose the L

and C component values depending on the loudspeaker impedance. Some typical values, which give a cutoff

frequency of 27 kHz, are shown in Figure 25. Typical LC filter for an 8 Ω speaker and Figure 26. Typical LC filter

for a 6 Ω speaker below.

Figure 25. Typical LC filter for an 8 Ω speaker

TDA7498L

Output low-pass filter

DS6539 - Rev 6

page 16/23