Datasheet

LNBH25L Application information
Doc ID 022634 Rev 2 5/28
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 the voltages (V
UP
) that let the integrated LDO post-regulator (generating the
13 V / 18 V LNB output voltages plus the 22 kHz DiSEqC™ tone) to 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 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
typically). The step-up converter soft-start function reduces the inrush current during
startup. The SS time is internally fixed at 4ms typ. to switch from 0 to 13 V and 6 ms typ. to
switch from 0 to 18 V.
2.1 DiSEqC data encoding (DSQIN pin)
The internal 22 kHz tone generator is factory trimmed in accordance to DiSEqC standards,
and can be activated in 3 different ways:
1. by an external 22 kHz source DiSEqC data connected to the DSQIN logic pin (TTL
compatible). In this case the I²C tone control bits must be set: EXTM = TEN = 1.
2. by an external DiSEqC data envelope source connected to the DSQIN logic pin. In this
case the I²C tone control bits must be set: EXTM=0 and TEN=1.
3. through the TEN I²C bit if a 22 kHz presence is requested in continuous mode. In this
case the DSQIN TTL pin must be pulled HIGH and EXTM bit set to “0”.
2.2 Data encoding by external 22 kHz tone TTL signal
In order to improve design flexibility an external tone signal can be input to the DSQIN pin by
setting the EXTM bit to “1”.
The DSQIN is a logic input pin which activates the 22 kHz tone to the V
OUT
pin, by using the
LNBH25L integrated tone generator.
The output tone waveforms are internally controlled by the LNBH25L 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 on the DSQIN pin, the EXTM and TEN bits must be previously set to “1”. As
soon as the DSQIN internal circuit detects the 22 kHz TTL external signal code, the
LNBH25L 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 ).
Figure 2. Tone enable and disable timing (using external waveform)
AM10426v1
~ 1 µs
~ 60 µs
DSQIN
Tone
Output