FET BIAS CONTROLLER WITH POLARISATION  
					SWITCH AND TONE DETECTION  
					ISSUE 2 - JUNE 2006  
					ZNBG3115  
					ZNBG3116  
					DEVICE DESCRIPTION  
					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.  
					Drain current setting of the ZNBG3115/16 is user  
					selectable over the range 0 to 15mA, this is achieved  
					with addition of a single resistor. The series also offers  
					the choice of drain voltage to be set for the FETs, the  
					3115 gives 2.2 volts drain whilst the 3116 gives 2 volts.  
					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 -2.8 volts, can also be used to  
					supply other external circuits.  
					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.  
					The ZNBG3115/16 includes bias circuits to drive up  
					to three external FETs. A control input to the device  
					selects either one of two FETs as operational, the  
					third FET is permanently active. This feature is  
					normally used as an LNB polarisation switch. Also  
					specific to Universal LNB applications is the 22kHz  
					tone detection and logic output feature which is  
					used to enable high and low band frequency  
					switching.  
					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.  
					Additionally each stage has its own individual current  
					limiter. 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 ZNBG3115/16 has been designed to cope with  
					DiSEqC™ ready set top boxes and rejects all  
					transients from channel switching.  
					The ZNBG3115/16 are available in QSOP16 and QSOP20  
					for the minimum in device size. Device operating  
					temperature is -40 to 80°C to suit a wide range of  
					environmental conditions.  
					FEATURES  
					APPLICATIONS  
					Provides bias for GaAs and HEMT FETs  
					Satellite receiver LNBs  
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					Drives up to three FETs  
					Private mobile radio (PMR)  
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					Dynamic FET protection  
					Cellular telephones  
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					Drain current set by external resistor  
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					Regulated negative rail generator requires only  
					2 external capacitors  
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					Choice in drain voltage  
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					Wide supply voltage range  
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					Polarisation switch for LNBs  
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					22kHz tone detection for band switching  
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					Tone detector ignores unwanted signals  
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					Support fr MIMIC, FET and Bipolar local  
					oscillator devices  
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					Compliant with ASTRA control specifications  
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					QSOP 16 and 20 surface mount packages  
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					ISSUE 2 - JUNE 2006