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Original question:

TPS62840: UVLO

TPS62840: Increase the battery lifetime

Ali
Prodigy 10 points
Part Number: TPS62840

Hi,

I want to use the TPS62840 in my project with an input voltage of 6.2V and an output of 1.8v. The output voltage will be connected to an MCU and one temperature sensor. The peak current of my devices is around 24 mA(20mA + 4mA). The input voltage is supplied by four coin cell batteries(Part number: SR41W with a nominal capacity of 45mA and standard discharge current of 70uA) in series. Since the peak current far exceeds the rated drain current condition (~80 uA) for which the battery capacity is stated in the battery datasheet, how can I increase the battery's lifetime? should I put a current limiter before the voltage regulator? Regarding the peak current of my project, should I consider additional capacitors in my project? I would appreciate it if you help me to overcome this issue.

You can find the datasheet of the battery at the following link.

https://media.digikey.com/pdf/Data%20Sheets/Seiko%20Instruments%20PDFs/SR41W_DS.pdf

Regards,
Ali

  • 0
    TI__Expert 3611 points

    Hi Ali,

    What is the load profile of your application? I am assuming you are supplying an SoC with BLE or another similar RF protocol.
    So I suppose that you are transmitting/receiving data for a short time and that is where the current peaks arise, whereas for most of the time the SoC would be in sleep mode well within the rated current of the battery.

    Having considered this, I would recommend adding some extra COUT in order to reduce the amount of current supplied from the battery itself and help with those transients. Please take a look at the following app-note which goes through a similar application: Coin cells and peak current draw, the equations which are used to size the input cap is described in the Appendix of that app-note.

    Regards,
    Davor

  • 0 in reply to Davor Pavlovski
    Prodigy 10 points

    Hi Davor,

    Thanks for your reply.

    I read the white paper before. The discharge current of CR2032 is around 15 mA while the discharge of current of my battery is around 80 uA. It is a big issue in my project and I don't know how can I manage it.

    I am supplying an SoC with BLE. the SoC should read data from the sensor and sent it to the central via BLE. As you rightly pointed out, for most of the time the SoC would be in sleep mode. 

     

    Regards,

    Ali

  • 0 in reply to Ali
    TI__Expert 3611 points

    Hi Ali,

    I have some more questions:

    1. Can you send the exact load profile you are expecting during normal operation? 
    2. Can you send a draft of your schematic? 
    3. Is there some kind of limitation that forces the use of those low-current batteries? Since there are other silver oxide batteries that can support higher current loads.

    Regards,
    Davor