LNBH221 datasheet(9/27 Pages) STMICROELECTRONICS

9 / 27 page

LD39150

Application information

9/27

Application information

Basically, the LNBH221 includes two circuits that are completely independent. Each circuit

can be separately controlled and must have its independent external components. All the

below specification must be considered equal for each section.

This IC has a built in DC/DC step-up controller that, from a single supply source ranging

from 8 to 15V, generates the voltages (VUP) that let the linear post-regulator to work at a

minimum dissipated power of 1W typ. @ 500mA load (the linear regulator drop voltage is

internally kept at: VUP-VOUT=2V typ.). An UnderVoltage Lockout circuit will disable the

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

internal 22KHz tone generator is factory trimmed in accordance to the standards, and can

be controlled either by the I2CTM interface or by a dedicated pin (DSQIN) that allows

immediate DiSEqCTM data encoding (*). When the TEN (Tone ENable) I2C bit it is set to

HIGH, a continuous 22KHz tone is generated on the output regardless of the DSQIN pin

logic status.

The TEN bit must be set LOW when the DSQIN pin is used for DiSEqCTM encoding. The

fully bi-directional DiSEqCTM 2.0 interfacing is completed by the built-in 22KHz tone

detector. Its input pin (DETIN) must be AC coupled to the DiSEqCTM bus, and the extracted

PWK data are available on the DSQOUT pin (*). To comply to the bi-directional DiSEqCTM

2.0 bus hardware requirements an output R-L filter is needed. The LNBH221 is provided

with two output pins: the VOTX to be used during the tone transmission and the VORX to be

used when the tone is received. This allows the 22KHz Tone to pass without any losses due

to the R-L filter impedance (see DiSeqC 2.0 application circuit on page 4). In DiSeqC 2.0

applications during the 22KHz transmission activated by DSQIN pin (or TEN I2C bit), the

VOTX pin must be preventively set ON by the TTX I

2C bit and, both the 13/18V power

supply and the 22KHz tone, are provided by mean of VOTX output. As soon as the tone

transmission is expired, the VOTX must be set to OFF by setting the TTX I

2C bit to zero and

the 13/18V power supply is provided to the LNB by the VORX pin through the R-L filter.

When the LNBH221 is used in DiSeqC 1.x applications the R-L filter is not required (see

DiSeqC 1.x application circuit on pag. 4), the TTX I2C bit must be kept always to HIGH so

that, the VOTX output pin can provide both the 13/18V power supply and the 22KHz tone,

enabled by DSQIN pin or by TEN I2C bit. All the functions of this IC are controlled via I2CTM

bus by writing 6 bits on the System Register (SR, 8 bits). The same register can be read

back, and two bits will report the diagnostic status. When the IC is put in Stand-by (EN bit

LOW), the power blocks are disabled.

When the regulator blocks are active (EN bit HIGH), the output can be logic controlled to be

13 or 18V by mean of the VSEL bit (Voltage SELect) for remote controlling of non-DiSEqC

LNBs. Additionally, the LNBH221 is provided with the LLC I2C bit that increase the selected

voltage value (+1V when VSEL=0 and +1.5V when VSEL=1) to compensate for the excess

voltage drop along the coaxial cable (LLC bit HIGH). By mean of the LLC bit, the LNBH221

is also compliant to the American LNB power supply standards that require the higher

output voltage level to 19.5V (typ.) (instead of 18V), by simply setting the LLC=1 when

VSEL=1. In order to improve design flexibility and to allow implementation of newcoming

LNB remote control standards, an analogic modulation input pin is available (EXTM).

An appropriate DC blocking capacitor must be used to couple the modulating signal source

to the EXTM pin. Also in this case, the VOTX output must be set ON during the tone

transmission by setting the TTX bit high. When external modulation is not used, the relevant

pin can be left open. The current limitation block is SOA type: if the output port is shorted to

ground, the SOA current limitation block limits the short circuit current (ISC) at typically

300mA or 200mA respectively for VOUT 13V or 18V, to reduce the power dissipation.

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