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LMP92064 IC Current sense interfacing issue

user458242
Prodigy 50 points

Other Parts Discussed in Thread: LMP92064

Hi 

I have assembled my power supply PCB with LMP92064 IC.

My requirement is as below:

1) Current and voltage is to be monitored on an isolated supply which powers my PCB:  +28V and +28V_RET 

2) IC is being powered (VDD,GND) and (VDIG,DGND)  from single supply (+5V and GND)

As the grounds are isolated i.e (+28_RET and GND) i am not able to read correct data on SDO Pin.

When i have shorted +28V_RET and GND then i am able to read current drawn on +28V.

How do i solve this problem?

If I give VDD and VDIG from a +5V  isolated DC/DC converter, would it solve my purpose.

Thanks in advance

Regards

Srinivas N

dsp_304@yahoo.com 

  • 0
    TI__Expert 4595 points
    Thank you for your question. Someone from the team will get back to you soon.
  • 0
    TI__Guru 69556 points
    Hello Srinivas,

    The current sense input is not a "floating" input. The voltage applied to the inputs can only go -0.3V to +2V away from GND. You cannot "split" (isolate) the grounds.

    You will need to power the LMP92064 from +5V on the the 28V ground side, and pass the data across the ground divide. It is generally easier to send the digital across the ground divide than DC signals (via optical or inductive methods).

    Simple opto-isolators are the easiest for SPI, but not cheap.

    See the LMP92064 Isolated Booster Pack EVM as an example

    www.ti.com/.../BOOST-LMP92064EVM

    Regards,