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Original question:

TPS65218D0: clarification on data sheet for AC_DET connection and also Queiscent current

TPS65218D0: Leakage Current

Amarnath Murugadass
Intellectual 480 points
Part Number: TPS65218D0
Other Parts Discussed in Thread: AM4378, TMDSEVM437X

Hi Sir/Madam,

For the Coin cell input pin of the TPS65218D0 will there be any leakage current or quiescent current when there is voltage available in the Vin_bu pins. 

We are in the process of calculating the size of the Coin cell required to provided backup for the RTC functionality in AM4378 and in datasheet they have provided the leakage current and quiescent current with condition as Vin_Bu as 0V. So please confirm if there will be any leakage/quiescent current when there is power available in Vin_bu

Regards,

M Amarnath

  • 0
    TI__Mastermind 30310 points

    There will be no leakage current from the coin cell battery resulting from the PMIC when VIN_BU is available.

    I am not an expert on batteries, but you still need to consider the effects of "self-discharge". Here is an article I found that might be helpful.

  • 0 in reply to Brian Berner
    Intellectual 480 points

    Hi Brian,

    Thanks for the update.

    Regarding the CC pin in the datasheet they have provided source impedance value of 1000 ohms. But in the TI General Purpose PCB the impedance used is 1400 ohms. Can you confirm if we can use 1400 ohms/1500 ohms in design as per the eval board? Will we face any issue due to the increased source impedance

    Datasheet

    Eval Board

    Thanks & Regards,

    M Amarnath

  • 0 in reply to Amarnath Murugadass
    TI__Mastermind 30310 points

    This definition of source impedance is different than the 1.4k resistor in the AM437x EVM (TMDSEVM437X).

    On the EVM schematic, above the screen shot where it cut off, do you see header J25? When you install a jumper across these 2 pins, R61 is shorted out.

    In my opinion, R61 should be marked as DNI or swapped out for a 10-Ohm current-limiting resistor. It is likely that R61 was used for testing but was not intended to be in the final design.

    The 1000 Ohms that you are seeing is the maximum source impedance that would be effective, which is a combination of trace loss + battery cage loss + internal resistance of the coin cell battery itself. The more source impedance, the more voltage drop from coin cell to CC pin, the less effective the battery will be (voltage will be unusable earlier). Hence, it is a maximum specification for a parasitic in the design.

    The current-limiting resistor is a common technique, but it is not critical to the design.