Mitsubishi Electric PSS**S72FT, Руководство пользователя

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<Dual-In-Line Package Intelligent Power Module>
1200V Mini DIPIPM with BSD Series APPLICATION NOTE
Publication Date: September 2015
12
3. Determination of Shunt Resistance
(1) Shunt resistance
The value of current sensing resistance is calculated by the following formula:
R
Shunt
= V
SC(ref)
/SC
where V
SC(ref)
is the SC trip voltage.
The maximum SC trip level SC(max) should be set less than the IGBT minimum saturation current which is
1.7 times as large as the rated current. For example, the SC(max) of PSS10S72FT should be set to
10x1.7=17A. The parameters (V
SC(ref)
, R
Shunt
) dispersion should be considered when designing the SC trip
level.
For example of PSS10S72FT, there is +/-0.03V dispersion in the spec of V
SC(ref)
as shown in Table 2-2-1.
Table 2-2-1 Specification for V
SC(ref)
(unit: V)
Condition Min Typ Max
at Tj=25°C, V
D
=15V 0.45 0.48 0.51
Then, the range of SC trip level can be calculated by the following expressions:
R
Shunt(min)
=V
SC(ref) max
/SC(max)
R
Shunt(typ)
= R
Shunt(min)
/ 0.95* then SC(typ) = V
SC(ref) typ
/ R
Shunt(typ)
R
Shunt(max)
= R
Shunt(typ)
x 1.05* then SC(min)= V
SC(ref) min
/ R
Shunt(max)
*)This is the case that shunt resistance dispersion is /-5%.
So the SC trip level range is described as Table 2-2-2.
Table 2-2-2 Operative SC Range (R
Shunt
=30m Ω (min), 31.6m Ω (typ), 33.2m Ω (max)
Condition min. typ. Max.
at Tj=25°C, V
D
=15V 13.5A 15.2A 17A
(e.g. 30m Ω (R
shunt(min)
)= 0.51V (=V
SC(max)
) / 17A(=SC(max))
There is the possibility that the actual SC protection level becomes less than the calculated value. This is
considered due to the resonant signals caused mainly by parasitic inductance and parasitic capacity. It is
recommended to make a confirmation of the resistance by prototype experiment.
(2) RC Filter Time Constant
It is necessary to set an RC filter in the SC sensing circuit in order to prevent malfunction of SC protection
due to noise interference. The RC time constant is determined depending on the applying time of noise
interference and the SCSOA of the DIPIPM.
When the voltage drop on the external shunt resistor exceeds the SC trip level, The time (t1) that the CIN
terminal voltage rises to the referenced SC trip level can be calculated by the following expression:
) 1 ln( 1
) 1 (
1
c shunt
SC
t
c shunt SC
I R
V
t
I R V

   
   




Vsc : the CIN terminal input voltage, Ic : the peak current, τ : the RC time constant
On the other hand, the typical time delay t2 (from Vsc voltage reaches Vsc(ref) to IGBT gate shutdown) of
IC is shown in Table 2-2-3.
Table 2-2-3 Internal time delay of IC
Item Min typ max Unit
IC transfer delay time - - 1.0 μ s
Therefore, the total delay time from an SC level current happened to the IGBT gate shutdown becomes:
t
TOTAL
=t1+t2