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LNBK10: DescriptionLNB SUPPLY AND CONTROL VOLTAGE REGULATOR PARALLEL INTERFACE; File Size522KB，25 Pages; ManufacturerSTMicroelectronics; Websitehttp://www.st.com/

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LNB SUPPLY AND CONTROL VOLTAGE REGULATOR PARALLEL INTERFACE

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LNBK20

LNB supply and control voltage regulator (parallel interface)

Feature summary

■

Complete interface for two LNBs remote supply

and control

LNB selection and stand-by function

Built-in tone oscillator factory trimmed at

22KHz

Fast oscillator start-up facilitates DiSEqC

encoding

Two supply inputs for lowest dissipation

Bypass function for slave operation

LNB short circuit protection and diagnostic

Auxiliary modulation input extends flexibility

Cable length compensation

Internal over temperature protection

Backward current protection

PowerSO-20

■

Description

Intended for analog and digital satellite receivers,

the LNBK is a monolithic linear voltage regulator,

assembled in PowerSO-20 and SO-20,

specifically designed to provide the powering

voltages and the interfacing signals to the LNB

downconverter situated in the antenna

-O

via the coaxial cable. It has the same functionality

of the LNBP1X and LNBP20 series, at a reduced

output current capability. Since most satellite

receivers have two antenna ports, the output

voltage of the regulator is available at one of two

logic-selectable output pins (LNBA, LNBB). When

the IC is powered and put in Stand-by (EN pin

LOW), both regulator outputs are disabled to

allow the antenna downconverters to be

supplied/controlled by others satellite receivers

sharing the same coaxial lines. In this occurrence

the device will limit at 3 mA (max) the backward

current that could flow from LNBA and LNBB

output pins to GND. (See continuous description).

SO-20

Order code

Packages

Part number

PowerSO-20

LNBK20

February 2007

LNBK20PD-TR

Rev. 8

SO-20

LNBK20D2-TR

Tape & Reel

1/25

www.st.com

Packaging

LNBK20

Description (continued)

For slave operation in single dish, dual receiver systems, the bypass function is

implemented by an electronic switch between the Master Input pin (MI) and the LNBA pin,

thus leaving all LNB powering and control functions to the Master Receiver. This electronic

switch is closed when the device is powered and EN pin is LOW.

The regulator outputs can be logic controlled to be 13 or 18 V (typ.) by mean of the VSEL

pin for remote controlling of LNBs. Additionally, it is possible to increment by 1V (typ.) the

selected voltage value to compensate the excess voltage drop along the coaxial cable (LLC

pin HIGH).

In order to reduce the power dissipation of the device when the lowest output voltage is

selected, the regulator has two Supply Input pins V

CC1

and V

CC2

. They must be powered

respectively at 16V (min) and 23V (min), and an internal switch automatically will select the

suitable supply pin according to the selected output voltage. If adequate heatsink is

provided and higher power losses are acceptable, both supply pins can be powered by the

same 23V source without affecting any other circuit performance.

The ENT (Tone Enable) pin activates the internal oscillator so that the DC output is

modulated by a ±0.3 V, 22KHz (typ.) square wave. This internal oscillator is factory trimmed

within a tolerance of ±2KHz, thus no further adjustments neither external components are

required.

A burst coding of the 22KHz tone can be accomplished thanks to the fast response of the

ENT input and the prompt oscillator start-up. This helps designers who want to implement

the DiSEqC

protocols

(a)

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.

When external modulation is not used, the relevant pin can be left open.

Two pins are dedicated to the overcurrent protection/monitoring: CEXT and OLF. The

overcurrent protection circuit works dynamically: as soon as an overload is detected in

either LNB output, the output is shut-down for a time T

off

determined by the capacitor

connected between CEXT and GND. Simultaneously the OLF pin, that is an open collector

diagnostic output flag, from HIGH IMPEDANCE state goes LOW.

After the time has elapsed, the output is resumed for a time t

=1/15t

off

(typ.) and OLF goes

in HIGH IMPEDANCE. If the overload is still present, the protection circuit will cycle again

through t

off

and t

until the overload is removed. Typical t

off

value is 1200ms when a

4.7µF external capacitor is used.

This dynamic operation can greatly reduce the power dissipation in short circuit condition,

still ensuring excellent power-on start up even with highly capacitive loads on LNB outputs.

The device is packaged in PowerSO-20 for surface mounting. When a limited functionality in

a smaller package matches design needs, a range of cost-effective PowerSO-10 solutions is

also offered. All versions have built-in thermal protection against overheating damage.

-O

a. External components are needed to comply to level 2.x and above (bidirectional) DiSEqC

bus hardware

requirements. DiSEqC

is a trademark or EUTELSAT.

3/25

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