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ZNBG2000 ZNBG2001
FET BIAS CONTROLLER
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. With the addition of two capacitors and a resistor the devices provide drain voltage and current control for 2 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 ZNBG2000/1 contains two bias stages. A single resistor allows FET drain current to be set to the desired level. The series also offers the choice of drain voltage to be set for the FETs, the ZNBG2000 gives 2.2 volts drain whilst the ZNBG2001 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 0.7V. 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 ZNBG2000/1 are available in MSOP10 packages for the minimum in devices size. Device operating temperature is -40 to 80C to suit a wide range of environmental conditions.
FEATURES
* Provides bias for GaAs and HEMT FETs * Drives up to two FETs * Dynamic FET protection * Drain current set by external resistor * Regulated negative rail generator requires only 2
external capacitors
APPLICATIONS
* Satellite receiver LNBs * Private mobile radio (PMR) * Single in single out C Band LNB * Cellular telephones
* Choice in drain voltage * Wide supply voltage range * MSOP surface mount package
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ZNBG2000 ZNBG2001
ABSOLUTE MAXIMUM RATINGS
Supply Voltage Supply Current Drain Current (per FET) (set by RCAL1 and RCAL2) -0.6V to 15V 100mA 0 to 15mA Output Current Operating Temperature Storage Temperature 100mA -40 to 80C -40 to 85C 500mW
Power Dissipation (Tamb 25 C)
MSOP10
ELECTRICAL CHARACTERISTICS TEST CONDITIONS (Unless otherwise
SYMBOL PARAMETER CONDITIONS Min V CC I CC V SUB E ND E NG fO Supply Voltage Supply Current Substrate Voltage (Internally generated) Output Noise Drain Voltage Gate Voltage Oscillator Freq. I D1 and I D2=0 I D1 and I D2 =10mA I SUB = 0 I SUB = -200A C G =4.7nF, C D =10nF C G =4.7nF, C D =10nF 150 330 -3.5 5 5 24 -2.8
LIMITS
Typ Max 12 10 30 -2 -2 0.02 0.005 800
UNITS
V mA mA V V Vpkpk Vpkpk kHz
DRAIN CHARACTERISTICS
I DO ID I DV I DT VD Output Current Range Current Current Change with V CC with T j Voltage V CC =5 to 12V T j =-40 to +80C ZNBG2000 I D1 and I D2 =10mA ZNBG2001 2 1.8 0.5 0.05 2.2 2 2.4 2.2 %/V %/C V V Set by R CAL1 0 8 10 15 12 mA mA
Voltage Change V DV V DT with V CC with T j V CC = 5 to 12V T j = -40 to +80C 0.5 50 %/V ppm
GATE CHARACTERISTICS
I GO V OL Output Current Range Output Voltage Output Low I D1 IG1 and I D2 =12mA and I G2 =0 -3.5 -3.5 0.4 -2 -2 1 V V V -40 2000 A
I D1 and I D2 =12mA I G1 and I G2 = -10A V OH Output High I D1 and I D2 = 8mA I G1 and I G2 = 0
Notes: 1. The negative bias voltages specified are generated on-chip using an internal oscillator. Two external capacitors, CNB and CSUB, of 47nF are required for this purpose. 2. The characteristics are measured using an external reference resistors RCAL1 of value 16k wired from pin RCAL1 to ground. 3. Noise voltage is not measured in production. 4. Noise voltage measurement is made with FETs and gate and drain capacitors in place on all outputs. CG, 4.7nF, are connected between gate outputs and
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ZNBG2000 ZNBG2001
TYPICAL CHARACTERISTICS
16
Vcc = 5V
Drain Current (mA)
14 12 10 8 6 4 2 0 0 10 20 30 40 50
0.0 -0.5
Note:- Operation with loads > 200A is not guaranteed.
Vsub (V)
-1.0 -1.5 -2.0 -2.5 -3.0 0 0.2
Vcc = 5V 6V 8V 10V
0.4
0.6
0.8
1.0
Rcal (k)
External Vsub Load (mA)
JFET Drain Current v Rcal
Vsub v External Load
2.4
ZNBG2000
2.2
ZNBG2001
Drain Voltage (V)
2.3
Drain Voltage (V)
2.1
2.2
Vcc = 5V 6V 8V 10V
2.0
Vcc = 5V 6V 8V 10V
2.1
1.9
2.0 2 4 6 8 10 12 14 16
1.8 2 4 6 8 10 12 14 16
Drain Current (mA)
Drain Current (mA)
JFET Drain Voltage v Drain Current
JFET Drain Voltage v Drain Current
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ZNBG2000 ZNBG2001
FUNCTIONAL DIAGRAM
FUNCTIONAL
DESCRIPTION
The ZNBG devices provide all the bias requirements for external FETs, including the generation of the negative supply required for gate biasing, from the single supply voltage. The diagram above shows a single stage from the ZNBG series. The ZNBG2000/1 contains 2 such stages. The drain voltage of the external FET QN is set by the ZNBG device to its normal operating voltage. This is determined by the on board VD Set reference, for the ZNBG2000 this is nominally 2.2 volts whilst the ZNBG2001 provides nominally 2 volts. The drain current taken by the FET is monitored by the low value resistor ID Sense. The amplifier driving the gate of the FET adjusts the gate voltage of QN so that the drain current taken matches the current called for by an external resistor RCAL. Both ZNBG devices have the facility to program different drain currents into selected FETs. Since the FET is a depletion mode transistor, it is usually necessary to drive its gate negative with respect to ground to obtain the required drain current. To provide this capability powered from a single positive supply, the device includes a low current negative supply generator. This generator uses an internal oscillator and two external capacitors, CNB and CSUB.
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ISSUE 1 - AUGUST 2001 4
ZNBG2000 ZNBG2001
TYPICAL APPLICATION CIRCUIT
APPLICATIONS
16k
INFORMATION
The above is a partial application circuit for the ZNBG series showing all external components required for appropriate biasing. The bias circuits are unconditionally stable over the full temperature range with the associated FETs and gate and drain capacitors in circuit. Capacitors CD and CG ensure that residual power supply and substrate generator noise is not allowed to affect other external circuits which may be sensitive to RF interference. They also serve to suppress any potential RF feedthrough between stages via the ZNBG device. These capacitors are required for all stages used. Values of 10nF and 4.7nF respectively are recommended however this is design dependent and any value between 1nF and 100nF could be used. The capacitors CNB and CSUB are an integral part of the ZNBGs negative supply generator. The negative bias voltage is generated on-chip using an internal oscillator. The required value of capacitors CNB and CSUB is 47nF. This generator produces a low current supply of approximately -3 volts. Although this generator is intended purely to bias the external FETs, it can be used to power other external circuits via the CSUB pin. Resistor RCAL1 sets the drain current at which all external FETs are operated. If any bias control circuit is not required, its related drain and gate connections may be left open circuit without affecting the operation of the remaining bias circuits. If all FETs associated with a current setting resistor are omitted, the particular RCAL should still be included. The supply current can be reduced, if required, by using a high value RCAL resistor (e.g. 470k). The ZNBG devices have been designed to protect the external FETs from adverse operating conditions. With a JFET connected to any bias circuit, the gate output voltage of the bias circuit can not exceed the range -3.5V to 0.7V, under any conditions including powerup and powerdown transients. Should the negative bias generator be shorted or overloaded so that the drain current of the external FETs can no longer be controlled, the drain supply to FETs is shut down to avoid damage to the FETs by excessive drain current. The following diagram show the ZNBG2000/1 in typical LNB applications.
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ZNBG2000 ZNBG2001
INFORMATION CONT.
APPLICATIONS
ZNBG2000/1
ZNBG2000/01 Pinout For MSOP10 Package Designator - X 1 D1 G1 GND CNB1 CNB2 VCC D2 G2 RCAL CSUB
ORDERING INFORMATION
Part Number ZNBG2000X10 ZNBG2001X10 Package MSOP10 MSOP10 Part Mark ZNBG2000 ZNBG2001 QTY Reel 4000 4000
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ZNBG2000 ZNBG2001
PACKAGE DIMENSIONS
EF
H G A C D a
B
K
DIM A B C D E
Millimetres 1.10 0.23 0.18 0.50 3.00
tol. MAX. +0.07 -0.08 60.05 BSC 60.1
DIM F G H K a
Millimetres 4.9 0.55 3.00 0.10 3.0
tol. 0.15 0.15 0.1 0.05 3.0
(c) Zetex plc 2001
Zetex plc Fields New Road Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4422 Fax: (44) 161 622 4420 Zetex GmbH Streitfeldstrae 19 D-81673 Munchen Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc Suite 315 700 Veterans Memorial Highway Hauppauge NY11788 USA Telephone: (631) 360 2222 Fax: (631) 360 8222 Zetex (Asia) Ltd 3701-04 Metroplaza, Tower 1 Hing Fong Road Kwai Fong, Hong Kong China Telephone: (852) 26100 611 Fax: (852) 24250 494
These offices are supported by agents and distributors in major countries world-wide. This publication is issued to provide outline information only which (unless agreed by the Company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. For the latest product information, log on to www.zetex.com
ISSUE 1 - AUGUST 2001 7

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