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BQ25505: How to set an external reference

Jennifer Segura
Prodigy 10 points
Part Number: BQ25505

Hi, I'm trying to figure out how to supply a constant reference voltage to the VREF_SAMP pin without adding another source. The input is a Microbial Fuel Cell (MFC) which has a maximum power point around 0.5V. I don't want the MFC to overdischarge. Knowing this, I want the reference voltage to the MPPT controller to be constant, but there don't seem to be any bias voltages at my disposal. What is the best way to work around this? 

Thanks!

  • 0
    TI__Guru**** 165886 points

    Hi Jennifer,

    Unfortunately, if you don't want the VREF_SAMP voltage to be relative to the open circuit voltage at VIN_DC, then you will have to provide a reference using external circuitry.  Shunt voltage references typically consume mA's of current. A low Iq linear regulator is probably your best bet.  http://www.ti.com/lit/ds/symlink/tps7a05.pdf is one example.  You would get the 0.8V output version and then voltage divide down to 0.5V.  You would have to power this from VSTOR = VBAT_SEC.

    Regards,

    Jeff