AN3338 datasheet(28/72 Pages) STMICROELECTRONICS

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Electrical characteristics and functions

AN3338

28/72

Doc ID 18441 Rev 4

For these reasons, the shunt resistor and the filtering components must be placed as close

as possible to the SLLIMM pins, for additional suggestions refer to

Section 5.1: Layout

suggestions.

The value of the current sense resistor can be calculated by following different guidelines,

functions of the design specifications, or requirements. A common criterion is presented

here based on the following steps:

•

Defining of the overcurrent threshold value (IOC_th). For example, it can be fixed

considering the IGBT typical working current in the application and adding 20-30% as

overcurrent.

•

Calculation of the shunt resistor value according to the conditioning network. An

example of the conditioning network is shown in

Figure 22. Further details can be

found in the user manuals listed (see References

7, References 8, and References 9).

•

Selection of the closest shunt resistor commercial value.

•

Calculation of the power rating of the shunt resistor, taking into account that this

parameter is strongly temperature dependent. Therefore, the power derating ratio of

the shunt resistor,

ΔP(T)%, shown in the manufacturer's datasheet, must be considered

in the calculation as follows:

Equation 4

where IRMS is the IGBT RMS working current.

For a proper selection of the shunt resistor, a safety margin of at least 30% is recommended

on the calculated power rating.

(

)

(

RMS

SHUNT

⋅

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