AN3352 Datasheet, PDF (7/26 Pages) STMicroelectronics – Dual LNB power supply based on the LNBH24L

AN3352
Block diagram and pin function description
Figure 3. DiSEqC 1.X tone burst with 22 kHz IC controller
High-Z
STATE
VoRx OUTPUT
High-Z
STATE
High-Z
STATE
Vtone signal
Push -pull
Action
Push -pull
Action
1.5
DiSEqC 1.X implementation through V_oTX and EXTM
If an external 22 kHz tone source is not available, it is possible to use the internal 22 kHz
tone generator signal available through the V_oTX pin to drive the EXTM pin. In this way the
V_oTX 22 kHz signal is superimposed to the V_oRX DC voltage to generate the LNB output 22
kHz tone (see Figure 6). The internal 22 kHz tone generator, available through the V_oTX pin,
must be activated during the 22 kHz transmission by the DSQIN pin or by the TEN bit. The
DSQIN internal circuit activates the 22 kHz tone on the V_oTX output with 0.5 cycles ± 25 µs
delay from the TTL signal present on the DSQIN pin, and it stops with 1 cycle ± 25 µs delay
after the TTL signal has expired. The V_oTX pin internal circuit must be preventively set ON by
the TTX function. This can be controlled both through the TTX pin and the I²C bit. As soon
as the tone transmission has expired, the V_oTX must be disabled by setting the TTX to LOW.
The 13/18 V power supply is always provided to the LNB from the V_oRX pin.
1.6
PDC optional circuit for DiSEqC 1.X applications using V_oTX
signal on to EXTM pin and 22 kHz tone controlled by DSQIN
pin
In some applications, at light output current (< 50 mA), having a heavy LNB output
capacitive load, the 22 kHz tone can be distorted. In this case it is possible to add the
“Optional” external components described on Section 2.7.
1.7
22 kHz oscillator
The internal 22 kHz tone generator is factory-trimmed in accordance with current standards
and can be selected by the I²C interface TTX bit (or TTX pin) and controlled by the DSQIN
pin (TTL compatible), which allows immediate DiSEqC data encoding. If the 22 kHz tone
presence is requested in continuous mode, the internal oscillator can be activated by the I²C
Doc ID 018526 Rev 3
7/26