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TPS61081EVM-147 mod

Shane Corbin
Prodigy 70 points
Other Parts Discussed in Thread: TPS61081

I plan to use this regulator evm to step up the voltage from a BQ Tesla wireless power receiver supplying 5V@1A to about 14.6V in order to charge a sealed lead acid battery, at a slow charge rate of about 300mA.  I have reviewed the schematics of the eval board and they match my design almost identically except for the fixed output voltage of 12V.  I am planning to change R2 of the feedback divider with a 39kOhm resistor and a 10kOhm trim pot in series in order to achieve 15Volts.  I understand that replacing R1 would be ideal but R2 will be much easier for me and if my estimates are correct it would only step up feedback current by about 100uA. I believe this would just be a loss in efficiency and will be dealt with in the migration from prototype status. I was just wondering if you had any advice on this.

Thank You in advance

Shane

  • 0
    TI__Genius 16870 points

    Hi Shane, 

    First off, thank you for your interest and  evaluation of TI's TPS61081. 

    As for your EVM modifications, you are on the right track. I am not sure if you require the POT for if you have a wide variety of resistors you can possibly just do some trail and error until you find the best value. Definitely, test this circuit and make sure you can output enough current at your minimum input voltage. 

    Question regarding changing R1 or R2: Technically, you can change either one get to the 15V output. Just stick around 50kOhms for R2 which you are and a high resistance for R1 which you are as well. 

    Good luck and don't hesitate to post more questions as they arise. 

  • 0 in reply to Michael Green
    Prodigy 70 points

    From what I understand as long as I can maintain 14.6V regardless of the exact current the battery should take a charge.  The length of time it takes to charge is not real important as the robot will not be used everyday, at least right now.  So a very slow charge is ok with me, providing I have not misunderstood the concept of slow charging and sealed lead acid batteries.

    Shane

  • 0 in reply to Shane Corbin
    TI__Genius 16870 points

    This is not what I was commenting on. I was basically saying that changing R2 with the 39k and 10k POT would be a reasonable practice for developing your new converter design. 

    To test with the battery I would suggest build your modified EVM. Test the circuit before you connect the battery with a 300mA resistive load then try using the battery.