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LMR38020: Negative Current

Brian Wang0928
Genius 14020 points
Part Number: LMR38020
Other Parts Discussed in Thread: TPS3762

Two Tech question for motor drive application. 

1. Negative Current

Customer would like to use a LMR38020 device to implement below functions. 

48Vin converts to 24Vout with 200mS, and then converter to 12Vout for load. Below is waveform. There is a negative current happened during 24V to 12V transient as waveform below. Is this acceptable?

2. We consider to use a supervisor TPS3762 to implement 200ms delay as below diagram. is it ok? Or any suggestion? Thanks. 

  • 0
    TI__Mastermind 30955 points

    Hi Brian,

    1) For the LMR38020, the part has a negative current limit down to -0.9A in FPWM. It looks like that is what is happening on the simulation. However, that looks a little strange, I wouldn't expect to see that if you are using another converter to get the 12V output. 

    2) Usually we do not recommend adding a supervisor like that to the feedback pin, as that is used to help the IC regulate the output voltage. What is the purpose of the delay here? If you want to do some sequencing, you may do that with the EN pin. 

    Thanks,

    Richard