LNBH26LS datasheet(7/33 Pages) STMICROELECTRONICS

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LNBH26LS

Application information (valid for each section

A/B)

DocID025504 Rev 1

7/33

Application information (valid for each section 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 (VUP) that let the integrated LDO post-regulator (generating the 13

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 VUP - VOUT =

1 V typ.). The IC is also provided with an undervoltage lockout circuit that disables the

whole circuit when the supplied VCC drops below a fixed threshold (4.7 V typically). 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

2.1

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) 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 the 22 kHz presence is requested in continuous mode. In this

case t

he DSQIN TTL pin must be pulled high and the 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 VOUT pin, by using the

LNBH26LS integrated tone generator.

The output tone waveforms are internally controlled by the LNBH26LS 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

LNBH26LS activates the 22 kHz tone on the VOUT 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 an external

waveform)".

Figure 2: Tone enable and disable timing (using an external waveform)

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