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TPS62745: Loop-Powered Application

Gerald
Genius 9570 points
Part Number: TPS62745

Hi Experts,

Our customer needs to know, whether the TPS62745DSSRIC is suitable for loop-powered devices (4-20mA). Expected output is 3.3V@10mA.

When they are powering at 3.6mA, The board is not powered ON. But  the IC is working fine at 5.6mA current.

The Regulator IC(TPS62745DSSR) is miss behaving in each board. The input voltage is 3.6mA loop current. Whether the silicon have some manufacturing tolerance.

Please advise. Thank you.

Best regards,
Gerald

  • 0
    TI__Expert 7320 points

    Hi Gerald,

    What do you mean the input voltage is 3.6mA? Do you mean the input current is limited to 3.6mA? If so, the device may not be able to power up since it need more current for driver and loading though the quiescent current is very low for this part. And what's the input voltage? 

    Gerald said:
    The input voltage is 3.6mA loop current.

    You can also directly send me the schematic if possible.

  • 0 in reply to Athos Zhao
    TI__Genius 9570 points

    Hi Athos, 

    Thank you for your response. The input is constant current source. The input voltage is limited to 8.7V at 3.6mA.
    Due to the current source input, the voltage will be very based on the load current.
    The system is working in loop powered input (4 - 20mA)

    Please check and let me know if you have any queries.

    Thank you and best regards,
    Gerald

  • +1 in reply to Gerald
    TI__Expert 7320 points

    Hi Gerald,

    If the input is 8.7V at 3.6mA, it is definitely not able to supply 3.3V at 10mA output.

    You can see the input power 8.7*3.6 is less than the output power 3.3*10 without taking the efficiency into consideration.

    Assume the efficiency is 0.85, the input power must be higher than 3.3*10/0.85=38mW to support the output.