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UCC29002:Shunt Resistor Placement Order for UCC29002 and INA238

KS
Prodigy 20 points
Part Number: UCC29002
Other Parts Discussed in Thread: INA238

Tool/software:

Hi, TI support team

I am designing a power system that uses both the UCC29002 (load share controller) and the INA238 (current and power monitor).

I have a few questions regarding shunt resistor usage:

If I use separate shunt resistors for each IC, connected in series on the low (return) side after the load, which IC should have its shunt placed closer to the load (i.e., earlier in the current return path)? Should the UCC29002 or the INA238 come first?

Alternatively, is it possible to connect both ICs to a single shared shunt resistor in parallel? If so, are there any specific precautions, such as buffering or impedance isolation, that need to be taken into account to ensure proper operation of both ICs?

Your guidance would be greatly appreciated to ensure optimal performance and reliable current sensing for both devices.

Best regards,

KS

  • 0
    TI__Mastermind 40020 points

    Hello KS, 

    I believe that both ICs can share the same shunt resistor.  I don't think there are any special precautions needed for the UCC29002. 
    I don't know much about the INA238, but I did see that it has a limited minimum CM input range to -0.3V, so make sure that the shunt voltage is always low enough under worst-case load or surge conditions to avoid dropping the INA input below -0.3V. 

     Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 20 points

    Dear Ulrich,

    Thank you for your response and the helpful guidance regarding the INA238's common-mode input range.

    As a follow-up, I’d like to ask for clarification on one additional point:
    When UCC29002 and INA238 share the same shunt resistor (connected in parallel), is there any risk of input impedance interaction or current draw from the sense pins of either IC that could affect the accuracy or operation of the other?

    Specifically:

    • Does either IC have non-negligible input bias current, or

    • Could the differing input structures (e.g., analog front-end of the INA238 vs. ISNS pin of the UCC29002) introduce loading effects, offsets, or interference when connected together across a single shunt?

    I'd like to confirm whether such parallel usage could cause subtle measurement errors or functional issues under precision or high-speed load transient conditions.

    Thank you again for your support.

  • +1 in reply to KS
    TI__Mastermind 40020 points

    Hello KS, 

    I can tell you that the UCC29002 has negligible bias current for the CS+ and CS- inputs. 
    The inputs to the UCC29002 should not interfere with or cause problems for the INA238 inputs. 
    Because of the extremely low resistance of the shunt resistor, neither device can affect the other device's measurements.
    There is no ISNS pin on the load-share controller. 

    For specific help on the use of the INA238 device, please start a new E2E posting using the "INA238" part number in the title so that the appropriate group can be notified to respond to your questions.

    Regards,
    Ulrich