Datasheet

LNBH23L Application information
Doc ID 15335 Rev 4 5/25
2 Application information
This IC has a built-in DC-DC step-up converter that, from a single source from 8 V to 15 V,
generates the voltages (V
UP
) that let the linear post-regulator to work at a minimum
dissipated power of 0.55 W typ. @ 500 mA load (the linear post-regulator drop voltage is
internally kept at V
UP
- V
OUT
= 1.1 V typ.). An under voltage lockout circuit will disable the
whole circuit when the supplied V
CC
drops below a fixed threshold (6.7 V typically).
Note: In this document the V
OUT
is intended as the voltage present at the linear post-regulator
output (V
oRX
pin).
2.1 DiSEqC™ data encoding
The internal 22 kHz tone generator is factory trimmed in accordance to the standards, and
can be selected by I²C interface TTX bit (or TTX pin) and activated by a dedicated pin
(DSQIN) that allows immediate DiSEqC™ data encoding, or through TEN I²C bit in case the
22 kHz presence is requested in continuous mode. In stand-by condition (EN bit LOW) The
TTX function must be disabled setting TTX to LOW. Besides the internal 22 kHz tone
generator, the auxiliary modulation pin (EXTM) can be driven by an external 22 kHz source
and in this case TTX must be set to low.
2.2 DiSEqC™ 1.X implementation by EXTM pin
In order to improve design flexibility and reduce the total application cost, an analogic
modulation input pin is available (EXTM) to generate the 22 kHz tone superimposed to the
V
oRX
DC output voltage. An appropriate DC blocking capacitor must be used to couple the
modulating signal source to the EXTM pin. If the EXTM solution is used the output R-L filter
can be removed (see Figure 5) saving the external components cost. If this configuration is
used keep TTX set to low.
The pin EXTM modulates the V
oRX
voltage through the series decoupling capacitor, so that:
V
oRX(AC)
= V
EXTM(AC)
x G
EXTM
Where V
oRX(AC)
and V
EXTM(AC)
are, respectively, the peak to peak voltage on the V
oRX
and
EXTM pins while G
EXTM
is the voltage gain from EXTM to V
oRX
.
2.3 DiSEqC™ 1.X implementation with V
OTX
and EXTM pin
connection
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. The V
oTX
pin
internal circuit must be preventively set ON by setting the TTX function to High. This can be
controlled both through the TTX pin or by I²C bit. By this way the V
oTX
22 kHz signal will be
superimposed to the V
oRX
DC voltage to generate the LNB output 22 kHz tone (see
Figure 3). After TTX is set to High the internal 22 kHz tone generator available through the
V
oTX
pin can be activated during the 22 kHz transmission either by 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 presence on the DSQIN pin, and it stops with 1 cycles ± 25
µs delay after the TTL signal is expired. As soon as the tone transmission is expired, the