AN-9044 - Fairchild Semiconductor
AN-9044 - Fairchild Semiconductor
AN-9044 - Fairchild Semiconductor
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DC Current<br />
Isc<br />
Rshunt<br />
Mini DIP (SPM3) Application Note (2012-07-09)<br />
© 2008 FAIRCHILD SEMICONDUCTOR - Smart Power Module<br />
RF<br />
34<br />
15V-Line<br />
+ +<br />
CSC<br />
VSEN VCSC<br />
- -<br />
Mini DIP SPM<br />
VCC<br />
CSC<br />
COM<br />
Figure 7.4 Example of Short Circuit protection circuit with 1-shunt resistor<br />
An RC filter (reference RF CSC above) is necessary to prevent noise related SC circuit malfunction.<br />
The RC time constant is determined by the applied noise time and the IGBT withstand voltage capability. It is<br />
recommended to be set in the range of 1.5 ~ 2s.<br />
When the external shunt resistor voltage drop exceeds the SC protection level, this voltage is applied<br />
to the CSC pin via the RC filter. The filter delay time (t1) is the time required for the CSC pin voltage to rises to<br />
the referenced SC protection level. Table 7.2 shows the specification of the SC protection level. The IC has<br />
an internal noise elimination logic filter delay (t2) of 500nsec. The typical IC transfer time delay (t3) should be<br />
considered, too. Please, refer to the table 7.3.<br />
Table 7.2 Specification of SC protection reference level ’ VSC(REF)’<br />
Item Min. Typ. Max. Unit<br />
SC trip level VSC(REF) 0.45 0.5 0.55 V<br />
Table 7.3 Internal delay time of SC protection circuit<br />
Item Min. Typ. Max. Unit<br />
Internal filter delay time (t2) - 0.5 0.7 sec<br />
IC transfer delay time (t3) - 0.9 1.3 sec<br />
Therefore the total time from the detection of the SC trip current to the gate off of the IGBT becomes:<br />
TTOTAL = t1 + t2 + t3
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