LNBH25S Datasheet, PDF (7/37 Pages) STMicroelectronics – LNB supply and control IC with step-up and IC interface

LNBH25S
Application information
2
Application information
This IC has a built-in DC-DC step-up converter that, from a single source (8 V to 16 V),
generates voltages (V_UP) which let the integrated LDO post-regulator (generating13 V/18 V
LNB output voltages plus 22 kHz DiSEqC™ tone) work with a minimum dissipated power of
0.5 W typ. @ 500 mA load (the LDO drop voltage is internally kept at V_UP-V_OUT = 1 V typ.).
The LDO power dissipation can be reduced when 22 kHz tone output is disabled by setting
the LPM bit to “1” see Section 2.4: "LPM (low power mode)". The IC is also provided with
an undervoltage lockout circuit that disables the whole circuit when the supplied V_CC drops
below a fixed threshold (4.7 V typ.). The step-up converter soft-start function reduces the
inrush current during startup. SS time is internally fixed at 4 ms typ. to switch from 0 to 13 V
and 6 ms typ. switch from 0 to 18 V.
2.1
DiSEqC data encoding (DSQIN pin)
The internal 22 kHz tone generator is factory trimmed in accordance with DiSEqC
standards, and can be active in 3 different ways:
1. By an external 22 kHz source DiSEqC data connected to the DSQIN logic pin (TTL
compatible). In this case I²C tone control bits have to be set: EXTM = TEN = 1.
2. By an external DiSEqC data envelope source connected to the DSQIN logic pin. In
this case I²C tone control bits must be set: EXTM = 0 and TEN = 1.
3. Through TEN I²C bit if the 22 kHz presence is requested in continuous mode. In this
case the DSQIN TTL pin must be pulled high and EXTM bit is set to “0”.
Each of the above solutions requires that during the 22 kHz tone activation and/or DiSEqC
data transmission, the LPM bit has to be set to “0” see Section 2.4: "LPM (low power
mode)".
2.2
Data encoding by external 22 kHz tone TTL signal
In order to improve design flexibility, an external tone signal can be input on the DSQIN pin
by setting the EXTM bit to “1”.
The DSQIN is a logic input pin, which activates the 22 kHz tone on VOUT pin, by using the
LNBH25S integrated tone generator.
The output tone waveforms are internally controlled by the LNBH25S tone generator in
terms of rise/fall time and tone amplitude, while, the external 22 kHz signal on the DSQIN
pin is used to define the frequency and the duty cycle of the output tone. A TTL compatible
22 kHz signal is required for the proper control of the DSQIN pin function. Before sending
the TTL signal to the DSQIN pin, the EXTM and TEN bits have to be previously set to “1”.
As soon as the DSQIN internal circuit detects the 22 kHz TTL external signal code, the
LNBH25S activates the 22 kHz tone on the V_OUT output with about 1 µs delay from TTL
signal activation, and it stops with about 60 µs delay after the 22 kHz TTL signal on DSQIN
has expired, refer to Figure 2: "Tone enable and disable timing (using external waveform)".
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