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VCR2N/4N/7N JFET Voltage-Controlled Resistors Product Summary Part Number VCR2N VCR4N VCR7N VGS(off) Max (V) -7 -7 -5 V(BR)GSS Min (V) -25 -25 -25 rDS(on) Max (W) 60 600 8000 Features D Continuous Voltage-Controlled Resistance D High Off-Isolation D High Input Impedance Benefits D Gain Ranging Capability/Wide Range Signal Attenuation D No Circuit Interaction D Simplified Drive Applications D Variable Gain Amplifiers D Voltage Controlled Oscillator D AGC Description The VCR2N/4N/7N JFET voltage controlled resistors have an ac drain-source resistance that is controlled by a dc bias voltage (VGS) applied to their high impedance gate terminal. Minimum rDS occurs when VGS = 0 V. As VGS approaches the pinch-off voltage, rDS rapidly increases. This series of junction FETs is intended for applications where the drain-source voltage is a low-level ac signal with no dc component. Key to device performance is the predictable rDS change versus VGS bias where: r DS(@ V GS + 0) V GS r DSbias [ 1V GS(off) These n-channel devices feature rDS(on) ranging from 20 to 8000 W. All packages are hermetically sealed and may be processed per MIL-S-19500 (see Military Information). TO-206AA (TO-18) TO-206AF (TO-72) S 1 S 1 4 C 2 D 3 G and Case D 2 3 G Top View VCR7N Top View VCR2N, VCR4N Updates to this data sheet may be obtained via facsimile by calling Siliconix FaxBack, 1-408-970-5600. Please request FaxBack document #70293. Applications information may also be obtained via FaxBack, request document #70598. Siliconix S-52424--Rev. D, 14-Apr-97 1 VCR2N/4N/7N Absolute Maximum Ratingsa Gate-Source, Gate-Drain Voltage . . . . . . . . . . . . . . . . . . . . . . . . -25 V Gate Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 mA Power Dissipationb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 mW Operating Junction Temperature Range . . . . . . . . . . . . . -55 to 175_C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . -65 to 200_C Lead Temperature (1/16" from case for 10 sec.) . . . . . . . . . . . . . 300_C Notes: a. TA = 25_C unless otherwise noted. b. Derate 2 mW/_C above 25_C. Specificationsa Limits VCR2N VCR4N VCR7N Parameter Static Gate-Source Breakdown Voltage Gate-Source Cutoff Voltage Gate Reverse Current Symbol Test Conditions Typb Min Max Min Max Min Max Unit V(BR)GSS VGS(off) IGSS IG = -1 mA, VDS = 0 V VDS = 10 V, ID = 1 mA VGS = -15 V, VDS = 0 V VGS = 0 V, ID = 10 mA -55 -25 -3.5 -7 -5 20 60 -25 -3.5 -7 -0.2 -25 V -2.5 -5 -0.1 nA Drain-Source On-Resistance rDS(on) VGS = 0 V, ID = 1 mA VGS = 0 V, ID = 0.1 mA 200 600 4000 8000 W Gate-Source Forward Voltage VGS(F) VDS = 0 V, IG = 1 mA 0.7 V Dynamic Drain-Source On-Resistance Drain-Gate Capacitance Source-Gate Capacitance rds(on) Cdg Csg VGS = 0 V, ID = 0 mA f = 1 kHz VGD = -10 V, IS = 0 mA f = 1 MHz VGS = -10 V, ID = 0 mA f = 1 kHz 20 60 7.5 7.5 200 600 3 3 4000 8000 1.5 pF 1.5 W Notes: a. TA = 25_C unless otherwise noted. b. Typical values are for DESIGN AID ONLY, not guaranteed nor subject to production testing. NCB NPA NT 2 Siliconix S-52424--Rev. D, 14-Apr-97 VCR2N/4N/7N Typical Characteristics Output Characteristics (VCR2N) 30 VGS(off) = -4 V 25 I D - Drain Current (mA) 20 15 10 5 0 0 0.2 0.4 0.6 0.8 1 VDS - Drain-Source Voltage (V) VGS = 0 V 0.8 I D - Drain Current (mA) -0.5 V -1.0 V -1.5 V -2.0 V -2.5 V -3.0 V 0 0 0.1 0.2 0.3 0.4 0.5 VDS - Drain-Source Voltage (V) 1.0 -1.5 V -2.0 V -2.5 V 0.6 -3.0 V -4.0 V -3.5 V Output Characteristics (VCR4N) VGS = 0 V 0.4 0.2 VGS(off) = -4.2 V Output Characteristics (VCR7N) 200 VGS(off) = -2.5 V VGS = 0 V 120 -0.5 V -1.0 V 80 -1.5 V 40 -2.0 V 0 0 0.2 0.4 0.6 0.8 1 VDS - Drain-Source Voltage (V) 160 I D - Drain Current (mA) Applications A simple application of a FET VCR is shown in Figure 1, the circuit for a voltage divider attenuator. R The output voltage is: VOUT = VIN rDS R + rDS It is assumed that the output voltage is not so large as to push the VCR out of the linear resistance region, and that the rDS is not shunted by the load. VIN - VGS + VCR VOUT The lowest value which VOUT can assume is: VOUT(min) = VIN rDS(on) R + rDS(on) Since rDS can be extremely large, the highest value is: Figure 1. Simple Attenuator Circuit VOUT(max) = VIN Siliconix S-52424--Rev. D, 14-Apr-97 3 |
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