LNBH23L datasheet(5/25 Pages) STMICROELECTRONICS

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LNBH23L

Application information

Doc ID 15335 Rev 4

5/25

Application information

This IC has a built-in DC-DC step-up converter that, from a single source from 8 V to 15 V,

generates the voltages (VUP) that let the linear post-regulator to work at a minimum

dissipated power of 0.55 W typ. @ 500 mA load (the linear post-regulator drop voltage is

internally kept at VUP - VOUT = 1.1 V typ.). An under voltage lockout circuit will disable the

whole circuit when the supplied VCC drops below a fixed threshold (6.7 V typically).

Note:

In this document the VOUT is intended as the voltage present at the linear post-regulator

output (VoRX pin).

2.1

DiSEqC™ data encoding

The internal 22 kHz tone generator is factory trimmed in accordance to the standards, and

can be selected by I²C interface TTX bit (or TTX pin) and activated by a dedicated pin

(DSQIN) that allows immediate DiSEqC™ data encoding, or through TEN I²C bit in case the

22 kHz presence is requested in continuous mode. In stand-by condition (EN bit LOW) The

TTX function must be disabled setting TTX to LOW. Besides the internal 22 kHz tone

generator, the auxiliary modulation pin (EXTM) can be driven by an external 22 kHz source

and in this case TTX must be set to low.

2.2

DiSEqC™ 1.X implementation by EXTM pin

In order to improve design flexibility and reduce the total application cost, an analogic

modulation input pin is available (EXTM) to generate the 22 kHz tone superimposed to the

VoRX DC output voltage. An appropriate DC blocking capacitor must be used to couple the

modulating signal source to the EXTM pin. If the EXTM solution is used the output R-L filter

can be removed (see Figure 5) saving the external components cost. If this configuration is

used keep TTX set to low.

The pin EXTM modulates the VoRX voltage through the series decoupling capacitor, so that:

VoRX(AC) = VEXTM(AC) x GEXTM

Where VoRX(AC) and VEXTM(AC) are, respectively, the peak to peak voltage on the VoRX and

EXTM pins while GEXTM is the voltage gain from EXTM to VoRX.

2.3

DiSEqC™ 1.X implementation with VOTX and EXTM pin

connection

If an external 22 kHz tone source is not available, it is possible to use the internal 22 kHz

tone generator signal available through the VoTX pin to drive the EXTM pin. The VoTX pin

internal circuit must be preventively set ON by setting the TTX function to High. This can be

controlled both through the TTX pin or by I²C bit. By this way the VoTX 22 kHz signal will be

superimposed to the VoRX DC voltage to generate the LNB output 22 kHz tone (see

Figure 3). After TTX is set to High the internal 22 kHz tone generator available through the

VoTX pin can be activated during the 22 kHz transmission either by DSQIN pin or by the TEN

bit.The DSQIN internal circuit activates the 22 kHz tone on the VoTX output with 0.5 cycles ±

25 µs delay from the TTL signal presence on the DSQIN pin, and it stops with 1 cycles ± 25

µs delay after the TTL signal is expired. As soon as the tone transmission is expired, the

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