LNBH26

Application information (valid for each section A/B)

Doc ID 022771 Rev 1

5/38

2

Application information (valid for each section A/B)

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),

/ 18 V LNB output voltages plus the 22 kHz DiSEqC™ tone) work with a minimum dissipated

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

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.

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 the DSQIN TTL pin must be pulled HIGH and the EXTM bit set to “0”.

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

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 to the DSQIN pin by

setting the EXTM bit to “1”.

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

activation, and it stops with about 60 µs delay after the 22 kHz TTL signal on DSQIN has

expired (refer to

Figure 2).