2.3

Data encoding by external DiSEqC envelope control through the DSQIN pin

If an external DiSEqC™ envelope source is available, it is possible to use the internal 22 kHz generator activated

during the tone transmission by connecting the DiSEqC™ envelope source to the DSQIN pin. In this case the I²C

tone control bits must be set: EXTM=0 and TEN=1. In this way the internal 22 kHz signal is superimposed on the

internal control circuit activates the 22 kHz tone output.

it stops with a delay time in the range of 15 µs to 60 µs after the 22 kHz TTL signal on DSQIN has expired, refer

to Figure 3. Tone enable and disable timing (using envelope signal).

~ 6 µs

15 µs ~ 60 µs

DSQIN

Tone

output

GIPG2601151226LM

2.4

LPM (low power mode)

In order to reduce total power loss, each section of the LNBH26S is provided with the LPM I²C bit that can be

activated (LPM=1) in applications where the 22 kHz tone can be disabled for long time periods. The LPM bit can

be set to “1” when the DiSEqC™ data transmission is not requested (no 22 kHz tone output is present); in this

consequently, the power loss inside the relative LNBH26S channel regulator is reduced too. For example, at 500

mA load, LPM=1, allowing a minimum LDO dissipated power of 0.3 W typ. It is recommended to set the LPM bit

to “0” before starting the 22 kHz DiSEqC™ data transmission; in this condition the drop voltage across the LDO is

kept to 1 V typ. Keep LPM=0 all times if LPM function is not used.

2.5

DISEQC™ 2.0 implementation

The built-in 22 kHz tone detector completes the fully bi-directional DiSEqC™ 2.0 interfacing. Each LNBH26S

section DETIN pin must be AC coupled to the DiSEqC™ bus, and extracted PWK data is available on the

corresponding DSQOUT pin. To comply with the bi-directional DiSEqC™ 2.0 bus hardware requirements, an

output R-L filter is needed (per each voltage output pin). In order to avoid 22 kHz waveform distortion during tone

transmission, each LNBH26S section is provided with a BPSW pin to be connected to an external transistor,

which allows the bypassing of the corresponding output RL filter in DiSEqC 2.x applications while in transmission

mode. Before starting tone transmission by means of the DSQIN pin, provide that the TEN bit is preventively set

to “1” and after ending tone transmission, provide that the TEN bit is set to “0”.

2.6

Output current limit selection

The linear regulators current limit threshold can be set by an external resistor connected to the ISEL pin. The

resistor value defines the output current limit by the equation:

IMAXtyp. = 16578

RSEL1.206

(1)

with ISET = 0

IMAXtyp. = 6452

RSEL1.159

(2)

with ISET = 1

LNBH26S

Data encoding by external DiSEqC envelope control through the DSQIN pin

DS8975 - Rev 5

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