ZNBG3211Q20TC【PDF 1/16 页】IC SW 3BIAS TONE H/V 2.2V 20QSOP

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FET BIAS CONTROLLER WITH POLARISATION

SWITCH AND TONE DETECTION

ISSUE 2 - FEBRUARY 2000

DEVICE DESCRIPTION

ZNBG3210

ZNBG3211

The ZNBG series of devices are designed to

meet the bias requirements of GaAs and

HEMT FETs commonly used in satellite

receiver LNBs, PMR cellular telephones etc.

with a minimum of external components.

With the addition of two capacitors and a

resistor the devices provide drain voltage and

current control for three external grounded

source FETs, generating the regulated

negative rail required for FET gate biasing

whilst operating from a single supply. This

negative bias, at -3 volts, can also be used to

supply other external circuits.

The ZNBG3210/11 includes bias circuits to

drive up to three external FETs. A control

input to the device selects either one of two

FETs as operational using 0V gate switching

methodology, the third FET is permanently

active. This feature is particularly used as an

LNB polarisation switch. Also specific to LNB

applications is the enhanced 22kHz tone

detection and logic output feature which is

used to enable high and low band frequency

switching. The detector has been specifically

designed to reject inerference such as low

frequency signals and DiSEqC ? tone bursts

- without the use of additional external

components.

Drain current setting of the ZNBG3210/11 is

user selectable over the range 0 to 15mA, this

FEATURES

is achieved with the addition of a single

resistor. The series also offers the choice of

FET drain voltage, the 3210 gives 2.2 volts

drain whilst the 3211 gives 2 volts.

These devices are unconditionally stable

over the full working temperature with the

FETs in place, subject to the inclusion of the

recommended gate and drain capacitors.

These ensure RF stability and minimal

injected noise.

It is possible to use less than the devices full

complement of FET bias controls, unused

drain and gate connections can be left open

circuit without affecting operation of the

remaining bias circuits.

In order to protect the external FETs the

circuits have been designed to ensure that,

under any conditions including power

up/down transients, the gate drive from the

bias circuits cannot exceed the range -3.5V

to 1V. Furthermore if the negative rail

experiences a fault condition, such as

overload or short circuit, the drain supply to

the FETs will shut down avoiding excessive

current flow.

The ZNBG3210/11 are available in QSOP20

for the minimum in device size. Device

operating temperature is -40 to 70°C to suit

a wide range of environmental conditions.

APPLICATIONS

Provides bias for GaAs and HEMT FETs

Drives up to three FETs

Dynamic FET protection

Drain current set by external resistor

Regulated negative rail generator

requires only 2 external capacitors

Choice in drain voltage

Wide supply voltage range

Polarisation switch for LNBs -

supporting zero volt gate switching

Satellite receiver LNBs

Private mobile radio (PMR)

Cellular telephones

topology.

22kHz tone detection for band switching

Compliant with ASTRA control

specifications

QSOP surface mount package

67-1

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