LNBH23 Datasheet, PDF (5/32 Pages) STMicroelectronics – LNBs supply and control IC with step-up and I²C interface

LNBH23
2
Application information
Application information
Note:
2.1
2.2
2.3
This IC has a built-in DC-DC step-up converter with integrated NMOS 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 0.375 W Typ. @ 500 mA load (the linear post-
regulator drop voltage is internally kept at V_UP-V_ORX=0.75 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).
In this document the output voltage (V_O) is intended as the voltage present at the linear
post-regulator output (V_ORX pin).
DiSEqC^TM data encoding and decoding
The new internal 22 kHz tone generator (patent pending) 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^TM 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.
DiSEqC^TM 2.0 implementation
The built-in 22 kHz tone detector completes the fully bi-directional DiSEqC^TM 2.0 interfacing
(see Note: 1). It’s input pin (DETIN) must be AC coupled to the DiSEqC^TM BUS, and
extracted PWK data are available on the DSQOUT pin. To comply to the bi-directional
DiSEqC^TM 2.0 bus hardware requirements an output R-L filter is needed. The LNBH23 is
provided with two output pins, one for the dc voltage output (V_oRX) and one for the 22 kHz
tone transmission (V_oTX). The V_oTX must be activated only during the tone transmission
while the V_oRX provides the 13/18 V output voltage. This allows the 22 kHz Tone to pass
without any losses due to the R-L filter impedance (see Figure 4 typ. application circuit).
During the 22 kHz transmission, in DiSEqC^TM 2.0 applications, activated by DSQIN pin or
by the TEN bit, the V_oTX pin must be preventively set ON by the TTX function. This can be
controlled both through the TTX pin and by I²C bit. As soon as the tone transmission is
expired, the V_oTX must be disabled by setting the TTX to LOW to set the device in the 22
kHz receiving mode. The 13/18 V power supply is always provided to the LNB from the V_oRX
pin through the R-L filter.
DiSEqC^TM 1.X implementation
When the LNBH23 is used in DiSEqC^TM 1.x applications the R-L filter is always needed for
the proper operation of the new 22 kHz tone generator (patent pending. See application
circuit). Also in this case, the TTX function must be preventively enabled before to start the
22 kHz data transmission and disabled as soon as the data transmission has been expired.
The tone can be activated both with the DSQIN pin or the TEN I²C 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.
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