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TPS61235P: CC Feature

Andres Perez
Prodigy 160 points
Part Number: TPS61235P

Hi,

I want to use the TPS61235 boost converter to step up voltage coming from a lipo battery that would be attached to a battery charger IC that has a power path feature which is where the input of the TPS61235 would come from. The battery is rated at 3.7V and 6000mAh. The load will be a raspberry pi 4 so I would want the TPS61235 to output 5.1V/3A. The current drawn from the load would vary from 1A to 2.5A so I would like to be able to output 3A. The raspberry Pi has an operating voltage of 4.75-5.25V. Should I use the constant current feature to limit the current to 3A? Is the CC feature even to limit the current? I had concerns as I read the boost converter datasheet and saw this. 

Does this mean that if the load draws more than 3A then it would lower the output voltage? I am worried as I would like for the converter to output 5.1V constantly to meet the Pi's requrements.

Thank you,

Andy

  • 0
    TI__Expert 7615 points

    Hi Andy,

    Thanks for reaching out. If you don't want the output current is larger than 3A, you still need to use the cc feature to limit the current, otherwise the maximum output current is decided by internal current limit which is larger than 3A. If not, you can disable this feature.

    For the other question:

    Andres Perez said:
    Does this mean that if the load draws more than 3A then it would lower the output voltage?

    Yes, your output voltage will be lower if the output current is larger than the current limit you set. You can set larger current limit or disable the cc feature if you don't care about the maximum output current. 

    Best Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 160 points

    Would it be a significant voltage drop? I do not think my rasberry pi 4 load will draw over 3A so I am not sure whether to go with the CC feature or not. What would be safer.

  • 0 in reply to Andres Perez
    TI__Expert 7615 points

    Hi Andy,

    The CC feature is used to protect your load when the output is larger than the current limit accidently, for example, when VOUT pin is short to ground, to achieve this it has to decrease VOUT. If your load doesn't draw over the current limit you set in normal conditions, the VOUT will not drop.

    Best Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 160 points

    So when current is accidently higher than the limit, what will happen to the current as the voltage drops?

  • 0 in reply to Andres Perez
    TI__Expert 7615 points

    Hi Andy,

    If it occurs, output current will be clamped to the value you set.

    Best Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 160 points

    Then what would happen? Would the voltage regulate back to 5V ? or will the boost constantly just output the lower voltage? Confused as to how this feature would regulate it back to 5v/3A if that were to be my ideal output.

  • +1 in reply to Andres Perez
    TI__Expert 7615 points

    Hi Andy,

    When the output current is lower than the current limit you set, VOUT will equal to regular voltage 5V. If the output current becomes larger than current limit, IOUT will be clamped to the value you set, VOUT will be depended on your load, VOUT=IOUT_limit * Rload.  When the output current decreases, VOUT will be regulate back to 5V.

    If 5V/3A is your ideal output, you should set the output current limit to a value which is larger than 3A.

    Best Regards,

    Nathan