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LMP8646: Battery protection circuit for a solar battery

Sakhi Gundeti
Prodigy 50 points
Part Number: LMP8646
Other Parts Discussed in Thread: LM3102

I want to build a battery protection circuit for an e-bike which will limit the current to 125A but will not cutoff if the current is exceeded.The battery voltage is 48V and is charged using solar energy. Can I use LMP8646 for this application? 

  • 0
    TI__Mastermind 21760 points
    Hello Sakhi,

    Thanks for considering to use Texas Instruments. With 48V as the common mode voltage applied to your inputs of the current shunt monitor, that is within the the recommended operating range of the LMP8646. The device supply will determine the max output voltage. You can design for your shunt and gain with this value. Your gain or shunt will be derived from Vsupply/(shunt*Imax ) or Vsupply/Gain/Imax with Imax being 125A. any current above 125A will simply rail the output to the supply and not damage the supply as long as the differential between IN+ and IN- does not exceed 6V. You could alternatively set Imax to a higher current but this will increase the lowest current value you will measure. The lower current measurement is affected by input bias and input offset voltage.
  • 0 in reply to Patrick Simmons
    Prodigy 50 points
    What is the maximum current that the LMP8646 can limit?
  • 0 in reply to Sakhi Gundeti
    Guru 140200 points
    Hi Sakhi.

    the LMP8646 alone is no current limiter. It must be used in combination with a voltage regulator. For this the LMP8546 must be installed within the feedback loop of regulator which sets the output voltage. Please read carefully section 8.2 of datasheet with all the given examples.

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 21760 points
    Hello Sakhi,

    As kai noted, the LMP8646 by itself does not limit the current. It simply measures the current through the shunt resistor. Alternatively, you could view the LMP8646 as a device that generates an output voltage based upon its gain setting and the voltage across the shunt resistor. This output voltage can be used in a feedback loop with a switch mode power supply (i.e. buck, boost, step-up/stepdown regulator/controller), like the LM3102. The switch mode power supply limits the current or has a max recommended sourcing current. If you proceed with the LM3102, that device has 2.5A max current limit. It is possible to have a higher or lower current limit, if you use a different switch mode power supply. If you stick with the LM3102 and the LMP8646 combination, to set a particular current limit will require you to have the LMP8646 output a voltage of 0.8V at the current level you want to limit the LM3102 to sourcing.