AN957 Datasheet, PDF (3/13 Pages) List of Unclassifed Manufacturers – Measuring HEXFETCharacteristics

Index
AN-957 (v.Int)
As with any semiconductor device, some of the characteristics of HEXFET Power MOSFETs are temperature dependent. For
tests in which there is significant heating of the HEXFET Power MOSFET, a low repetition rate should be used. For tests
involving a slow transition through the linear region, a damping resistor of at least 10 ohms should be connected in series with
the gate, close to the gate lead to prevent oscillations. If frequent testing of MOS-gated devices is expected, the use of a test
fixture that plugs directly into the curve tracer would save a significant amount time. Such a fixture is descibed in Section 12.
MOS-gated transistors are static sensitive. Wrist straps, grounding mats and other ESD precautions must be followed, as
indicated in INT-955.
2. BV_DSS
This is the drain-source breakdown voltage (with V_GS = 0). BV_DSS should
be greater than or equal to the rated voltage of the device, at the specified
leakage current.
PER
V
50
E
R
T
µA
DIV
1. Connect the device as follows: drain to “C”, gate to “B”, source to
“E”.
2. Set the MAX PEAK VOLTS to 350V.
PER
H
50
O
R
Z
V
DIV
3. Set the SERIES RESISTOR to limit the avalanche current to a safe
value (i.e., tens of milliamps). A suitable value in this case would be
14 kOhms.
4. Set the POLARITY switch to NPN.
5. The MODE control should be set to NORM.
6. HORIZONTAL VOLTS/DIV should be set at 50 volts/div on the
"collector" range.
Figure 2. Drain-source breakdown voltage
7. VERTICAL CURRENT/DIV should be set at 50 microA/div.
8. On the plug-in fixture, the CONNECTION SELECTOR should be set to “SHORT” in the “EMITTER GROUNDED” sector.
This action grounds the gate and disables the step generator.
9. Connect the device using the LEFT/RIGHT switch. Increase the collector supply voltage using the VARIABLE
COLLECTOR SUPPLY control until the current (as indicated by the trace on the screen) reaches 250 microA. (See Figure
2.) Read BV_DSS from the screen.
3. I_DSS
This is the drain current for a drain-source voltage of 100% of rated
voltage, with V_GS = 0. This measurement is made in the same manner as
BV_DSS, except that:
1. The MODE switch is set to “LEAKAGE”.
2. Connect the device using the LEFT/RIGHT switch and adjust the
collector supply voltage to the rated voltage of the HEXFET Power
MOSFET (200V for the IRF630). Read the value of I_DSS from the
display (see Figure 3). The vertical sensitivity may need altering to
obtain an appropriately sized display. Often I_DSS will be in the
nanoamp range and the current observed will be capacitor currents
due to minute variations in collector supply voltage.
PER
V
1
E
R
T
ηA
DIV
PER
H
50
O
R
Z
V
DIV
Figure 3. Drain-source leakage current
4. V_GS(th)
This is the gate-source voltage which produces 250 microA of drain current (V_DS = V_GS). At this gate-source voltage the device
enters the active region. In circuits where devices are connected in parallel, switching losses can be minimized by using devices
with closely matched threshold voltages. This test requires the gate to be connected to the drain and conducted as follows:
1. Connect the device as follows: source to “E”, gate to “B”, drain to “C”. This connection arrangement may require the
construction of a special test fixture. Bending of the device leads can cause mechanical stress which results in the failure of
the device.
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