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LNBH23LQTR Datasheet(PDF) 5 Page - STMicroelectronics |
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LNBH23LQTR Datasheet(HTML) 5 Page - STMicroelectronics |
5 / 25 page LNBH23L Application information Doc ID 15335 Rev 4 5/25 2 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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