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Original question:

TPS2660: Internal wiring resistance between RTN to GND

TPS2660: RTN to GND Resistance of TPS2661 during various conditions

Andrew Goett12
Prodigy 70 points
Part Number: TPS2660
Other Parts Discussed in Thread: TMUX1237

Hello, 

I noticed in a previous E2E post it was mentioned that the RTN to GND resistance will be approximately 10-ohms when ~SHDN is not pulled low (ie, the E-Fuse is enabled) and there is no reverse polarity condition on VIN. 

previous post -> https://e2e.ti.com/support/power-management/f/196/t/704683

I wondered what the condition would be when ~SHDN is pulled low (ie, EFUSE in low power mode).

Question: for these conditions, what is the resistance between RTN and GND? What is the leakage current on the RTN pin? 

1. ~SHDN pulled low, VIN greater than minimum operating input voltage, not in reverse polarity mode

2. ~SHDN pulled low, VIN equal to 0V

  • 0
    TI__Guru* 96061 points

    Hi Andrew,

    Thanks for reaching out!

    We have not characterized the resistance between RTN and GND.

    1. ~SHDN pulled low, VIN greater than minimum operating input voltage, not in reverse polarity mode

    Resistance = ~10-Ohm and Since impedance is low, the current at RTN pin depends on the external voltage you apply at RTN pin

    2. ~SHDN pulled low, VIN equal to 0V

    Resistance is in the order of 100's of kOhm and similarly the current at RTN pin depends on the external voltage you apply at RTN pin

    By the way, why this information is important for your system ?

    Best Regards, Rakesh

  • 0 in reply to Rakesh
    Prodigy 70 points

    Hi Rakesh, thanks for the reply. 

    The reason why this question is important to me is because our design is using one ADC input to measure the voltage from two different EFUSES imon signals. So knowing reliably knowing what that rtn to ground resistance is will help make our imon measurements accurate. 

    Here is a simplified diagram of our imon measurement network. Depending on the voltages at the VIN and ~SHDN signals (those pins are not shown) the resistance of RTN will vary. 

    This imon configuration has similarities to other parallel efuse configurations I've seen in TI app notes..The main difference is, we only are ever using one EFUSE or the other for passing power. This means that at some times the RTN signals will be connected to each other (example #1 above) but some times the RTN signals will be high impedance. 

    Do you have any specific guidance on a imon measurement network configured in this way?

  • 0 in reply to Andrew Goett12
    TI__Guru* 96061 points

    Hi Andrew,

    I think, it will have impact on the measurement. For example, in the case where second eFuse is OFF, the ADC input will be voltage divider output of 100k and (100k+24.9k+RTN-to-GND resistance of second eFuse). The result output depends on whether the second eFuse is disabled or un-powered as RTN-to-GND resistance varies accordingly.

    An analog mux switch (such as TMUX1237) before the ADC to select the node of interest can be used. 

    Best Regards, Rakesh