LNBH25

Application information

Doc ID 022433 Rev 4

5/34

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) to work with a minimum

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

tone output is disabled by setting the LPM bit to “1” (see

2.4: LPM (low power mode)). The

IC is also provided with an undervoltage lockout circuit that disables the whole circuit when

function reduces the inrush current during start-up. The SS time is internally fixed at 4 ms

typ. to switch from 0 to 13 V and 6 ms typ. 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”.

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”.

LNBH25 integrated tone generator.

The output tone waveforms are internally controlled by the LNBH25 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 LNBH25

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

expired (refer to

Figure 2).