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TPS65910: TPS65910

Avi Amitai
Prodigy 160 points
Part Number: TPS65910
Other Parts Discussed in Thread: AM3356,

Hi

We are using the TPS65910 with the AM3356

My question is about the Vbackup.

We have rechargeable ML2430 (100mAH) coin battery ,

in P12 there is a mention for series resistor for Vbackup , is it a must to place it between the PMIC and the battery ? or its the internal resistance of the PMIC ?

Regards,

Avi

  • 0
    TI__Mastermind 30280 points
    This is not the internal resistance of the PMIC.

    It may be easier to understand if "Series Resistor" were written as "Ballast Resistor for battery or superCap" instead. It only needs to be added for a range of 5mF to 2000mF, which is the same allowable range for a battery or superCap at VBACKUP.

    If a standard 1-40uF capacitor is used at VBACKUP to supply VRTC for very short time periods, the ballast resistor is not needed. The CBB shown at VBACKUP in the Functional Block Diagram on page 2 of the datasheet is a 40uF electrolytic capacitor because there is no additional series resistor shown.

    The additional external ballast resistor is simply to limit the amount of current that could be sunk into a depleted superCap or battery and limit the current that a load could instantaneously pull from the superCap or battery when only the backup battery is present.


    The conversion from 100mAh to Farads is not direct, but a 100F superCap charged to 3.6V is roughly equivalent to 100mAh, so the backup battery you are using is considerably larger than 2000 mF (2 F). There is not a recommendation for series resistance on a battery of this size, but it would be simple to install a 1-10 Ohm power resistor (1206 package) and you can test performance with a few values (including 0 Ohms).

    Keep in mind that the Backup battery charging current is spec'd as 500uA typical in section 5.12 on page 19 of the TPS65910 datasheet, and you will need to see if your battery will work with such a small charging current.