Block diagram and pin function description

AN3352

6/26

Doc ID 018526 Rev 3

1.4

DiSEqC™ 1.X implementation through EXTM pin

output voltage. If the EXTM pin is used, the internal 22 kHz generator must be kept OFF

(TTX pin or TTX bit set LOW). A cheaper circuit must be used to couple the modulating

signal source to the EXTM pin (see Figure 2).

where:

and EXTM pin

In order to avoid the 22 kHz tone distortion, a dummy output load may be necessary, strictly

dependent on the output bus capacitance.

For the correct DiSEqC implementation, during tone transmission, it is most important that

the DiSEqC_out pin of the 22 kHz IC controller, is set in low impedance and vice versa,

during no-tone transmission, it must be set in high impedance.

Figure 2 shows an example circuit as an appropriate solution with a 22 kHz IC controller to

drive the EXTM pin for the DiSEqC implementation.

Table 2.

Output load

Output bus capacitance

Output load

< 50 nF

10 mA

250 nF (EUTELSAT spec.)

30 mA

750 nF (DIRECT TV spec.)

80 mA

Figure 2.

EXTM example of use with 22 kHz IC controller

AM09363v1

DISEQC_OUT

15 K

EXTM pin

LNBH24L

22 KHz IC

controller

1µF

VDD 3V3

R1

R2

C1

VoRx OUTPUT

R3

Vtone signal

VoRX