LNBH21 データシートの表示（PDF） - STMicroelectronics

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LNBH21

LNB SUPPLY AND CONTROL IC WITH STEP-UP CONVERTER AND I2C INTERFACE

STMicroelectronics 

LNBH21

APPLICATION INFORMATION

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

1.65W typ. @ 750mA load (the linear regulator drop voltage is internally kept at: VUP-VO=2.2V 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 LNBH21 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 5). In DiSeqC 2.0 applications

during the 22KHz transmission

preventively set ON by the TTX

activated by DSQIN

I2C bit and, both the

pin (or

13/18V

TEN I2C bit), the VOTX pin

power supply and the 22KHz

must

tone,

be

are

OprFoFvidbeydsebtytinmgetahneoTfTVXOTI2XC

output. As

bit to zero

soon as

and the

the tone transmission

13/18V power supply

is

is

expired,

provided

the VOTX must be set to

to the LNB by the VORX

pin through the R-L filter. When the LNBH21 is used in DiSeqC 1.x applications the R-L filter is not

required (see DiSeqC 1.x application circuit on pag.5), the TTX I2C bit must be kept always to HIGH so

that, the VOTX output

DSQIN pin or by TEN

pin

I2C

can

bit.

provide

both

the

13/18V

power

supply

and

the

22KHz

tone,

enabled

by

All the functions of this IC are controlled via I2C TM 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 18 V by mean of the VSEL bit (Voltage SELect) for

remote controlling of non-DiSEqC LNBs.

Additionally, the LNBH21 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 LNBH21 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 and it is possible to select two current limit thresholds, by the

dedicated ISEL pin. The higher threshold is in the range of 750mA to 1A if the ISEL is left floating or

connected a voltage > 3.3V. The lower threshold is in the range of 450mA to 700mA when the ISEL pin is

connected to ground. When the output port is shorted to ground, the SOA current limitation block limits the

short circuit current (ISC) at typically 400mA or 200mA respectively for VO 13V or 18V, to reduce the power

dissipation. Moreover, it is possible to set the Short Circuit Current protection either statically (simple

current clamp) or dynamically by the PCL bit of the I2C SR; when the PCL (Pulsed Current Limiting) bit is

set to LOW, the overcurrent protection circuit works dynamically, as soon as an overload is detected, the

output is shut-down for a time TOFF, typically 900ms. Simultaneously the OLF bit of the System Register

is set to HIGH. After this time has elapsed, the output is resumed for a time TON=1/10TOFF (typ.). At the

end of TON, if the overload is still detected, the protection circuit will cycle again through TOFF and TON. At

the end of a full TON in which no overload is detected, normal operation is resumed and the OLF bit is

reset to LOW. Typical TON+TOFF time is 990ms and it is determined by an internal timer. This dynamic

operation can greatly reduce the power dissipation in short circuit condition, still ensuring excellent

power-on start up in most conditions.

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