LNBH26 STMicroelectronics, LNBH26 Datasheet - Page 5

• Manufacturer Part Number: LNBH26
• Description: Dual LNB supply and control IC with step-up and I2C interface
• Manufacturer: STMicroelectronics

LNBH26
2
2.1
2.2
Application information (valid for each section A/B)
The LNBH26 includes two completely independent sections. Except for ISEL, V
inputs, each circuit can be separately controlled and have their independent external
components. All the specifications below must be considered equal for both sections (A/B).
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
/ 18 V LNB output voltages plus the 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
1 V typ.). The LDO power dissipation can be further reduced when 22 kHz tone output is
disabled by setting the LPM bit to “1” (see LPM function description). The IC is also provided
with an undervoltage lockout circuit that disables the whole circuit when the supplied V
drops below a fixed threshold (4.7 V typ.). The step-up converter soft-start function reduces
the in-rush current during startup. The SS time is internally fixed at 4 ms typ. to switch from
0 to 13 V, and 6 ms typ. to switch from 0 to 18 V.
DISEQC™ data encoding (DSQIN pin)
The internal 22 kHz tone generator is factory trimmed in accordance with the DiSEqC™
standards, and can be activated in 3 different ways:
1.
2.
3.
Each of the above solutions requires that during the 22 kHz tone activation and/or
DiSEqC™ data transmission, the LPM bit must be set to “0” [see
mode)
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
LNBH26 integrated tone generator.
The output tone waveforms are internally controlled by the LNBH26 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 LNBH26
activates the 22 kHz tone on the V
activation, and it stops with about 60 µs delay after the 22 kHz TTL signal on DSQIN has
expired (refer to
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.
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.
through the 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 the EXTM bit set to “0”.
].
Figure 2
).
UP
) that let the integrated LDO post-regulator (generating the 13 V
Doc ID 022771 Rev 1
OUT
Application information (valid for each section A/B)
output with about 1 µs delay from TTL signal
2.4: LPM (low power
OUT
pin, by using the
CC
UP
and I²C
- V
OUT
CC
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