LNBH25 datasheet(6/34 Pages) STMICROELECTRONICS

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Application information

LNBH25

6/34

Doc ID 022433 Rev 4

Figure 2.

Tone enable and disable timing (using external waveform)

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 to the VOUT DC voltage to

generate the LNB output 22 kHz tone. During the period in which the DSQIN is kept HIGH,

the internal control circuit activates the 22 kHz tone output.

The 22 kHz tone on the VOUT pin is activated with about 6 µs delay from the DSQIN TTL

signal rising edge, and it stops with a delay time in the range from 15 µs to 60 µs after the 22

kHz TTL signal on DSQIN has expired (refer to

Figure 3).

Figure 3.

Tone enable and disable timing (using envelope signal)

2.4

LPM (low power mode)

In order to reduce total power loss, the LNBH25 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); at this condition the drop voltage across the integrated

LDO regulator (VUP-VOUT) is reduced to 0.6 V typ. and, consequently, the power loss inside

the LNBH25 linear 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; at this condition the drop voltage

across the LDO is kept to 1 V typ. Keep LPM=0 at all times in case the 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.

The input pin (DETIN) must be AC coupled to the DiSEqC BUS, and extracted PWK data is

available on the DSQOUT pin. To comply with the bi-directional DiSEqC 2.0 bus hardware

AM10426v1

~ 1 µs

~ 60 µs

DSQIN

Tone

Output

AM10427v1

~ 6 µs

15 µs ~ 60 µs

DSQIN

Tone

Output

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