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LM5121-Q1: Can we use series disconnection FET Rds ON for current sensing

Part Number: LM5121-Q1
Other Parts Discussed in Thread: LM5121

Hi,

I am going to use LM5121 for 5V to 10V@6A

Can we use series disconnection switch Rds,on for current sensing instead of Current sensing resistor  to reduce the component and converter size?

With regards,

Selvam.

  • Hello Selvam,

    I did never test this and need some time to get back with an answer.

  • Hi Selvam,

    Usually, we would recommend to not use the series disconnection switch Rds,on because the tolerance with the rds-on may generate a large swing in the current limit, which may damage the disconnection FET. It may be better to use the current sense resistor. 

    Additionally, CSP and CSN pin only allow a maximum differential voltage of 0.3V. if the switch opens, the CSP and CSN pin on the part will be damaged as well. Therefore, in order for the part to not exceed maximum rating, the switch must always be on, which defeats the purpose of disconnection switch.  

    Thanks,

    Richard