AN957 Datasheet, PDF (9/13 Pages) List of Unclassifed Manufacturers – Measuring HEXFETCharacteristics

Index
LOW
10:1
2000 pF
AN-957 (v.Int)
CB or
DVM
Turn-on Delay
HIGH
Time, Rise Time,
Turn-Off Delay
Time, Fall Time
10M
D
Data sheet value
are for a resistive
load, as shown in
Figure 20, as well
as individual data
sheets.
The
gate
F_pi_ug_lsu_er_se 19. Test circuit for transfe^Rr^Gcapac^Gitance
should be just long enough to achieve
+
S
complete turn-on, with a duty cycle of the
10V
order of 0.1%.
-
25V
R_D
V_DS
0.5 x RATED V_DS
TO THE
OSCILLOSCOPE
V_GS
The series resistor is as specifyed in the data
sheet. The definitions of rise, fall and delay
times are given in Figure 21.
Figure 20. Test circuit for switching times
Power MOSFETs can switch in nanoseconds. Unless the test circuit is laid-out with RF techniques, the measurements will be
totally unreliable. Switching time measurements frequently amount to a characterization of the test circuit, rather than the device
under test. Gate charge provides a better indication of the switching capability of power MOSFETs.
Q_g, Q_gs, Q_{gd Total Gate Charge, Gate-Source Charge, Gate-Drain Charge}
The total gate charge has two
components: the gate-source charge
90%
V_DS
and the gate-drain charge (often
called the Miller charge).
INT-944 gives more details on this
test. Figures 22 and 23 show the test
circuit and waveforms.
10%
From the relationship Q = ∫i, the
following results are obtained:
V_GS
t_d(on)
ON DELAY
t_r
t_doff
OFF DELAY
t_f
TIME
RISE TIME
TIME
FALL TIME
Figure 21. Switching time waveforms
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