LNBH25LS

Application information

DocID026753 Rev 3

7/30

2

Application information

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 power of 0.5 W typ. @ 500 mA load (the LDO drop voltage is internally kept at

The step-up converter soft-start function reduces the inrush 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 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 VOUT pin, by using

the LNBH25LS integrated tone generator.

The output tone waveforms are internally controlled by the LNBH25LS 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 se

t to “1”. As

soon as the DSQIN internal circuit detects the 22 kHz TTL external signal code, the

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)".

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