Application Note
26 of 53
V 1.0
2019-04-01
IM393 Application note
IM393 IPM Technical Description
Function and protection circuit
Table 11
IGBT short-circuit ratings
Item
Symbol
Condition
Value
Unit
Short-circuit withstand time
T
SC
T
J
< 150 °C, V
DC
= 360 V, V
DD
= 15 V
3
μs
5.1.2
Selecting current-sensing shunt resistor
The value of the current-sensing resistor is calculated by the following equation:
OC
TH
IT,
SH
I
V
R
+
=
(1)
Where
+
TH
IT,
V
is the ITRIP positive-going threshold voltage of IM393-XX. It is typically 0.49 V. I
OC
is the current of
OC detection level.
The maximum value of the OC protection level should be set lower than the repetitive peak collector current in
the datasheet considering the tolerance of the shunt resistor.
For example, the maximum peak collector current of IM393-L6E/F is 22.5 A
peak
, and thus, the recommended
value of the shunt resistor is calculated as
(
)
=
0.49
22.5 = 0.022
Ω
For the power rating of the shunt resistor, the following list should be considered:
•
Maximum load current of inverter (I
RMS
)
•
Shunt resistor value at Tc = 25
°
C (R
SH
)
•
Power derating ratio of shunt resistor at T
SH
= 100
°
C according to the manufacturer’s datasheet
•
Safety margin
The shunt resistor power rating is calculated by the following equation:
ratio
derating
margin
R
I
P
SH
2
rms
SH
×
×
=
(2)
For example with IM393-L6E/F and R
SH
= 22 m
Ω
:
•
Max. load current of the inverter : 6 A
RMS
•
Power derating ratio of shunt resistor at T
SH
=100
°
C : 80 %
•
Safety margin : 30 %
W
0.9
0.8
1.3
0.022
5
P
2
SH
=
×
×
=
A proper power rating of shunt resistor should then exceed 1 W, e.g. 1.5 W.
Based on the previous equations, conditions, and calculation method, the minimum shunt resistance and
resistor power according to IM393-XX products have been introduced and are listed in Table 12.
Note that a proper resistance and power rating, which is higher than the minimum value, should be chosen
considering the over-current protection level required in the application.