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UCD3138PSFBEVM-027: About low side gate driver (UCC27424) and shunt resistor.

sunho lee1
Prodigy 100 points
Part Number: UCD3138PSFBEVM-027
Other Parts Discussed in Thread: TIDM-PSFB-DCDC, UCC27424

Hello.

On the schematic of UCD3138PSFBEVM and TIDM-PSFB-DCDC, the shunt resistor is located in low sided.

Also, its looks like it measure the voltage from output inductor current, not output DC current. 

Anyway, the ground pin of gate driver for synchronous rectifier (UCC27424) is connected to both source of SR and shunt resistor, not System ground (SGND).

Now, the First question is that is it any difference that ground pin of SR gate driver located SGND instead of both source of SR and shunt resistor.

And is it any problem if i connect the GND pin of gate driver into SGND, not source of SR as like above picture.

Second question : For example, votlage of GND pin of gate driver will be higher than the SGND in very high output current application.

Then, i think it will be affect the high/low condition of DPWM signal from digital controller (because both ground reference is different).

The question is somewhat vague, but please explain.

Thanks

  • 0
    TI__Genius 14580 points

    Hello,

    They are good questions. The drive IC is close to MOSFET, and it needs to supply high current to MOSFET, so the MOSFET's source should have the same ground as drive IC. The input of drive IC is a logic signal, it can handle some noise if there is some voltage crossing shunt. Of course, the shunt has very small resistance, a milli-ohm, maybe less for very large current. Just need be careful about how much voltage drop is on this shunt.

    Regards,
    Sean

  • 0 in reply to Sean Xu
    Prodigy 100 points

    Thanks for the answer Sean Xu. 

    Therefore, in summary on your answer, it will be ok that connect the ground pin of Gate driver into Source of MOSFET? 

    In fact, I was confused by seeing a lot of cases where other gate drivers or IPMs including low-sided shunt resistors,

    connect their ground to the system's ground rather than the switch's source (emitter).

    Thanks!

  • 0 in reply to sunho lee1
    TI__Guru**** 189399 points

    Hi, Sunho,

    As long as your voltage is within the Recommended Operating Conditions, you should be fine.