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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4
System performance
In Chapter 4 some measurement results are introduced. These measurements are intended to demonstrate
that the the system is fully operationa,l and that clear measurement data can be derived.
4.1
Short circuit mesurements
Since the overcurrent or short-circuit protection is an important function of the gate driver IC 1ED020I12-F2,
some measurements are presented here. Figure 13 illustrades the main functionality of the overcurrent
shutdown using DESAT functionality.
Figure 13
Circriuty for DESAT functionality
On the left-hand side of Figure 13, a section of the internal circuitry of the gate driver is shown schematically.
The internal power source delivers a constant current of around 500 µA and is connected to the internal
comparator and the DESAT pin. A charging capacitor
C
DESAT
, a resistor
R
DESAT
and a fast high voltage diode
V
F
with
the smallest possible capacitance are connected to the external DESAT -sense pin as shown in Figure 13. The
cathode of the high voltage diode is connected directly to the drain of the SiC MOSFET. This diode prevents the
high voltage from reaching the gate driver.
The DESAT module only works when the driver is switched on, i.e. when the gate driver switches on the power
switch via input “IN”. In this case, a so-called leading-edge blanking time (
t
DESATleb
) is expected, during which no
action is taken. This represents a delay time, which ignores certain disturbances or oscillations caused by the
switch-on process. Of course, no short circuit should be displayed here.
After that time, the capacitor is released and a part of the current from the internal current source charges the
capacitor. Another part of the current flows through the resistor and the diode through the drain. In normal
operation (no error case) an equilibrium is established. The voltage
V
C_DESAT
can be calculated using Equation 2
from Figure 14, and should be significantly lower than 9 V.
If an error occurs, e.g. an excessively high current due to a short circuit, the voltage
V
DS
(from SiC MOSFET in
this case) will increase. If the voltage at the drain is too high, the diode
V
F
closes and the internal current source
will charge the capacitor
C
DESAT
only. If the voltage on the capacitor exceeds 9 V, the internal comparator will
D
G
S
R
DESAT
I
DESAT
500µA
9 V
V
REF
x
Comparator
V
DS
V
F
V
R
_
DESAT
C
D
E
S
A
T
V
C
_
DESAT
DESAT
sense pin
DESAT
control
1EDI020I12-F2
IN