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LMP8640: LMP8640

Sanjeev Pandey
Prodigy 30 points

Part Number: LMP8640

I am using LMP8640 having gain = 50,  for current sensing. It gets saturated if current is more tham 0.4 A through the current sensing resistor (0.05 Ohm sensing resistor is used). What could be the possible reasons? 

I am using it to measure current through the inductor in a boost dc-dc converter.

  • 0
    TI__Genius 14825 points
    Sanjeev,

    By my calculations, you are expecting 1V output but instead you are seeing the positive supply rail? What is your supply rail? Could you share your schematic; at least the part with the current sensor? It will help us debug your circuit more quickly.

    Thank you.
  • 0 in reply to Jason Bridgmon
    Prodigy 30 points

    Hi,

    I am attaching complete schematic with supply range. Please let me know if you need any more information from my side. 

  • 0 in reply to Sanjeev Pandey
    TI__Genius 15770 points

    Hi Sanjeev,

    Please perform a quick DC test to make sure the LMP8640 is working in a linear fashion. 

    1. Turn the switch off

    2. Apply DC voltage at Vg: 15V, 20V and 25V (for 3 different measurements).

    3. You should measure Vout ~ (Vg-Vdiode)/Rload * Rshunt * 50V/V

    4. Record actual measurement. For example:

    With Rload = 50 ohms

    If this DC test is not possible, please let us know what is the saturated output voltage. Also, we would need for you to measure the differential voltage input of the LMP8640 (inputs 3 and 4). Please note this is a unidirectional device, so make sure you have the right polarities. 

  • 0 in reply to Mayrim Verdejo
    TI__Mastermind 32395 points
    Hello Sanjeev,

    In addition to Mayrim's test I have some questions,

    1. How are you measuring the current?
    2. How fast are you switching the MOSFET?
    3. Are you seeing the problem when the ADC is not connected to the LMP8640?

    I would try Mayrim's test with the ADC disconnected from the circuit as well to ensure that the ADC is not presenting a capactive load that the LMP8640 cannot drive.

    Peter Iliya
    Current Shunt Monitors Applications