LNBS21 datasheet(8/19 Pages) STMICROELECTRONICS

8 / 19 page

LNBS21

8/19

- no acknowledge, stopping the read mode

communication.

While the whole register is read back by the µP,

only the two read-only bits OLF and OTF convey

di-agnostic informations about the LNBS21.

Values are typical unless otherwise specified

POWER-ON I2C INTERFACE RESET

TheI2C

interfacebuilt

theLNBS21

automatically reset at power-on. As long as the

Vcc stays be-low the UnderVoltage Lockout

threshold (6.7V typ.), the interface will not respond

to any I2C com-mand and the System Register

(SR) is initialised to all zeroes, thus keeping the

power blocks disabled. Once the Vcc rises above

7.3V, the I2C interface becomes operative and the

SR can be configured by the main µP. This is due

to About 500mV of hysteresis provided in the UVL

threshold to avoid false retriggering of the

Power-On reset circuit.

DiSEqCTM IMPLEMENTATION

The LNBS21 helps the system designer to

implement the bi-directional (2.x) DiSEqC protocol

al-lowing

easy

PWK

modulation/

demodulation of the 22KHz carrier. The PWK data

are exchanged between the LNBS21 and the

main µP using logic levels that are compatible with

both 3.3 and 5V mi-crocontrollers. This data

exchange is made through two dedicated pins,

DSQIN and DSQOUT, in or-der to maintain the

timing relationships between the PWK data and

the PWK modulation as accurate as possible.

These two pins should be directly connected to

two I/O pins of the µP, thus leaving to the resident

firmware the task of encoding and decoding the

PWK data in accordance to the DiSEqC pro-tocol.

Full compliance of the system to the specification

is thus not implied by the bare use of the LNBS21.

The

system

designer

should

also

take

consideration the bus hardware requirements,

that include the source impedance of the Master

Transmitter measured at 22KHz. To limit the

attenuation at car-rier frequency, this impedance

has to be 15ohm at 22KHz, dropping to zero ohm

at DC to allow the power flow towards the

peripherals. This can be simply accomplished by

the LR

termination put on the OUT pin of the

LNBS, as shown in the Typical Application Circuit

on page 5.

Unidirectional (1.x) DiSEqC and non-DiSEqC

systems normally don't need this termination, and

the OUT pin can be directly connected to the LNB

supply port of the Tuner. There is also no need of

Tone Decoding, thus, it is recommended to

connect the DETIN and DSQOUT pins to ground

to avoid EMI.

ADDRESS PIN

Connecting this pin to GND the Chip I2C interface

address is 0001000, but, it is possible to choice

among 4 different addresses simply setting this

pin at 4 fixed voltage levels (see table on page

10).

ELECTRICAL CHARACTERISTICS FOR LNBS SERIES (TJ = 0 to 85°C, EN=1, LLC=0, TEN=0, ISEL=0,

PCL=0, DSQIN=0, VIN=12V, IOUT=50mA, unless otherwise specified. See software description section

for I2C access to the system register)

PCL

ISEL

TEN

LLC

VSEL

OTF

OLF

Function

These bits are read exactly the same as

they were left after last write operation

TJ<140°C, normal operation

TJ>150°C, power block disabled, Loothrough switch open

IOUT<IOMAX, normal operation

IOUT>IOMAX, overload protection triggered

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

VIN

Supply Voltage

IO = 750 mA TEN=VSEL=LLC=1

VLT1

LT1 Input Voltage

IIN

Supply Current

IO = 0mA TEN=VSEL=LLC=1

EN=1

EN=0

2.55mA

Output Voltage

IO = 750 mA VSEL=1

LLC=0

17.3

18.7

LLC=1

Output Voltage

IO = 750 mA VSEL=0

LLC=0

12.5

13.5

LLC=1

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