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LM3429: LM3429: IS current sense

Part Number: LM3429

Dear Sir,

My customer would use LM3429 to design a Buck-boost circuit LED Driver.

He saw LM3429 IS have different connect method(as red circle):  MOSFET Drain side & MOSFET Source side_ current sense resistor.

Could you kindly help explain two method of benefit ? what is recommend ?



  • Hi Steven,

    Figure 34 uses the RDSon of the FET as a sense resistor.  With this method, the sense current will vary with the type of FET use and will change over temperature since RDSon of FET changes with temperature.  Designed properly it can be made to work with the cost reduction of the sense resistor but there is complications because of RDSon variation.

    Figure 32 is the traditional current sense method which is accurate and does not vary with temperature or different FET's and I would recommend this.

    Thanks Tuan