User Guide EVAL-1ED020I12F2-DB
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v1.0
2021-06-21
EVAL-1ED020I12F2-DB user guide
Isolated driver daughter board to evaluate 1200 V CoolSiC™ MOSFET
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Figure 15 shows how the measurement works with an ohmic load resistor in a low-side configuration. As soon
as the gate voltage rises (blue line) to 15 V (switch-on process), the phase voltage (yellow line) falls to below
1 V, and the drain current (red line) of Q2 (or load current) increases to approximately 17 A. The DESAT voltage
( green dashed line ) rises to almost 6 V after the leading-edge blanking time.
The switch-off process begins with the falling edge of the gate voltage. The phase voltage increases to
approximate 800 V, and the load current drops down to 0 A. The DESAT output switches off and discharges the
DESAT capacitor. The short intermediate peak looks like a capacitive behavior of the diode
V
F
and the very high
du/dt (drain voltage) of approximately 23.400 V/µs.
4.1.2
Example measurement 2: short circuit at low-side
The second measurement example is shown in Figure 16 to and demonstrates a short-circuit measurement in
low-side configuration. In this case, the load as shown in Figure 7 is replaced by a short cable.
Figure 16
Short ciruit measurement at low-side configuration
The switch-on process is the same as in the previous measurement. The only difference is that no resistor is
connected in between. The pulse length at the input of the driver is the same at 5 µs. As soon as the gate
voltage increases, the load current increases rapidly up to approxivmately 330 A. Due to the very high current,
the phase voltage briefly drops from arround 800 V to 280 V, but recovers after several hundrets nanoseonds. It
can be observed clearly that the current strength decreases slightly. This is related to the fact that the MOSFET
heats up, and thus the internal resistance increases.
The voltage on the DESAT pin behaves as described in Chapter 4.1. After the leading-edge blanking time
(
t
DESATleb
), the DESAT capacitor (
C
DESAT
) charges in time
t
DESAT
. From a DESAT voltage of 9 V, the driver is switched
is
off internally. After another internal time delay (
t
DESATOUT
), the output switches off and the current begins to
decrease. In this setup, the entire process takes about 780 ns.