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TPS3613-01: Current draw on coincell battery

Andrew Darrow
Prodigy 90 points
Part Number: TPS3613-01

Hello, 

We currently use the TPS3613-01 to manage battery backup for the SRAM (SRAM part number: IS62WV51216BLL-55TLI) on our PCB. We are trying to determine the battery life of the coincell battery if our product is powered off (unplugged).

The coincell we are using is a CR2450 with a typical capacity of 620 mAh.

Our electronics technician measured a current draw of 54.5uA on the battery. This number is higher than expected and we are trying to determine why. The only thing directly connected to the battery is the TPS3613-01, and then the SRAM is connected to VOUT on the TPS3613-01.

I've looked at the datasheet for the TPS3613-01, but it is not clear to me how much current the device should draw from the battery. Once we know what the TPS3613-01 should be drawing, that might help us narrow down our problem.

Here is a relevant snippet from our schematic:

  • 0
    TI__Genius 9375 points

    Hi Andrew,

    The device itself has up to 40 uA of supply current, and my guess is that the rest could be going into the resistor divider on the SENSE pin. How much current are you expecting?

    Thanks,
    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Prodigy 90 points

    Hi Abhinav,

    We initially believed the SRAM would draw around 4 uA but after looking at the SRAM datasheet closer, it looks like that number is probably higher.

    When you say the device itself has up to 40 uA of supply current, is that the correct number to use when VBAT is connected to VOUT? And does that mean the device itself consumes 40 uA to perform it's supervisor functions? Or is that the total amount that it can draw from battery, including it's own consumption and the SRAM connected to it?

    To clarify, we want to know how much current the supervisor chip itself draws to perform its supervisor function when main power is disconnected and VOUT has been connected to VBAT.

    Could you please explain these parameters on the datasheet?

    I am not exactly sure what these parameters mean, especially the VOUT = VBAT line for VDD supply current. Why would there still be current on VDD if VOUT is connected to VBAT?

  • 0 in reply to Abhinav.Sharma
    Prodigy 90 points

    Please see my other comment for additional details.

  • 0
    Prodigy 90 points

    Hello , could you please respond? Thanks.

  • 0 in reply to Andrew Darrow
    TI__Genius 9375 points

    Hi Andrew,

    The supply current still applies when VBAT is connected to VOUT on the device.The device consumed 40 uA of current itself. Since the power the SRAM can draw can vary, we can only specify what the device uses for supervisory functions.

    Thanks,
    Abhinav.