AN957 ETC

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Technical content

AN-957 (v.Int) Measuring HEXFET  Characteristics (HEXFET is the trademark for International Rectifier Power MOSFETs) Topics covered:

  • Converting the nomenclature from bipolars to MOSFETs
  • P-Channel HEXFET Power MOSFETs
  • Initial settings
  • Breakdown
  • Drain leakage
  • Gate threshold
  • Gate leakage
  • Transconductance
  • On-resistance
  • Diode drop
  • Characteristics in synchronous rectification
  • Transfer characteristics
  • Measurements without a curve tracer
  • Device capacitances
  • Switching times
  • Gate charge
  • Reverse recovery
  • A fixture to speed-up testing time
  • Related topics 1. General Curve tracers have generally been designed for making measurements on bipolar transistors. While power MOSFETs can be tested satisfactorily on most curve tracers, the controls of these instruments are generally labeled with reference to bipolar transistors, and the procedure to follow in the case of MOSFETs is not immediately obvious. This application note describes methods for measuring HEXFET Power MOSFET characteristics, both with a curve tracer and with special-purpose test circuits. Testing HEXFET Power MOSFETs on a curve tracer is a simple matter, provided the broad correspondence between bipolar transistor and HEXFET Power MOSFET features are borne in mind. Table 1 matches some features of HEXFET Power MOSFETs with their bipolar counterparts. The HEXFET Power MOSFET used in all the examples is the IRF630. The control settings given in the examples are those suitable for the IRF630. The user must modify these values appropriately when testing a different device. The IRF630 was selected since it is a typical mid-range device with a voltage rating of 200 volts and a continuous current rating of 9 amps (with T C = 25°C). For measurements with currents above 20 amps, or for pulsed tests not controlled by the gate, the Tektronix 176 Pulsed High Current Fixture must be used instead of the standard test fixture. The IRF630 is an N-channel device. For a P-channel device, all the test procedures are the same except that the position of the Polarity Selector Switch must be reversed—that is, for P-channel devices, it must be in the PNP position. The curve tracer used as an example in this application note is a Tektronix 576, since this instrument is in widespread use. However, the principles involved apply equally well to other makes and models. Figure 1 shows the layout of the controls of the Tektronix 576 curve tracer, with major controls identified by the names used in this application note. Throughout this application note, when controls are referred to, the name of the control is printed in capitals. For all tests, when the power is on, the initial state of the curve tracer is assumed to be as follows:
  • LEFT/ RIGHT switch in “off” position
  • VARIABLE COLLECTOR SUPPLY at zero
  • DISPLAY not inverted
  • DISPLAY OFFSET set at zero
  • STEP/OFFSET POLARITY button OUT (not inverted)
  • VERT/HORIZ DISPLAY MAGNIFIER set at NORM (OFF)
  • The REP button of the STEP FAMILY selector should be IN
  • The AID button of the OFFSET selector should be IN
  • The NORM button of the RATE SELECTOR should be IN

Figure 1. Location of controls in a 576 curve tracer potential of the collector supply.

Figure 17. Test circuit for input capacitance Figure 18. Test circuit for output capacitance Figures 17, 18 and 19 show the circuit connections for the three capacitances that characterize power MOSFETs.

10 MΩΩ S

Figure 16. Test circuit for transconductance

AN-957 (v.Int) POSITION MEASUREMENT COMMENT 1I GSS C sense disconnected, Drain Source S/C connected, Collector Voltage applied to gate via 330Ω resistor. Note: Gate protected by back to back 30V zeners. 2R DS(on) Collector Voltage applied to DrainBased Voltage applied to Gate via 330Ω resistor. 3B VDSS / IDSS / VDS Collector Voltage applied to Drain, Gate Source S/C connected via 330Ω resistor. 4V GS(th) Collector Voltage applied to Drain, Gate Drain S/C connected via 330Ω resistor. Related topics: Parameter definition in IGBTs Gate Charge Thermal characteristics ESD sensitivity ESD test methods

AN-957 (v.Int) WORLD HEADQUARTERS: 233 Kansas St., El Segundo California 90245, Tel: (310) 322 3331 EUROPEAN HEADQUARTERS: Hurst Green, Oxted, Surrey RH8 9BB, UK Tel: ++ 44 1883 732020 IR CANADA: 7321 Victoria Park Ave., Suite 201, Markham, Ontario L3R 2Z8, Tel: (905) 475 1897 IR GERMANY: Saalburgstrasse 157, 61350 Bad Homburg Tel: ++ 49 6172 96590 IR ITALY: Via Liguria 49, 10071 Borgaro, Torino Tel: ++39 11 451 0111 IR FAR EAST: K&H Bldg., 2F, 3-30-4 Nishi-Ikeburo 3-Chrome, Toshima-Ki, Tokyo Japan 171 Tel: 81 3 3983 0086 IR SOUTHEAST ASIA: 315 Outram Road, #10-02 Tan Boon Liat Building, Singapore 0316 Tel: 65 221 8371 Data and specification subject to change without notice.

AN-957 (v.Int)