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Original question:

BQ25570: Multiple device with Single Storage element.

BQ25570: Multiple BQ25570 in parallel?

Max Holliday
Prodigy 40 points
Part Number: BQ25570

Hello,

In a previous question, BQ25570: Multiple device with Single Storage element, it was established multiple BQ25570's can be used in parallel to charge a storage device.

However, user Ricardo notes that the output of the BQ25570 buck regulators should NOT be connected. Why is this the case?

Background:

I would like to have more headroom above the ~100mA output capability of the BQ25570 buck regulator for the VOUT 3.3V rail I am using to power a microcontroller + sensors. While I'm at it, it would also be nice to charge the battery at a faster rate than 100mA. Therefore, since I have multiple solar panel boards I am working with, it seems natural to give each panel its own BQ25570 charging + output circuit. That is: connect the VBAT pins together and the VOUT pins together of multiple BQ25570.

Is there something flawed with this approach? 

  • 0
    TI__Guru**** 166996 points

    Hi Max,

    You can connect the VBAT outputs of multiple BQ25570 to the same storage element.  But you cannot connect the VIN_DC inputs to same solar panel because the MPPT circuit will not function correctly as they are not synched. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Thanks for the insight, Jeff!

    Understood about VIN_DC- but my question is connecting the VOUT output of multiple BQ25570 together. Any thoughts?

  • 0 in reply to Max Holliday
    TI__Genius 10385 points

    Max,

    The issue with tying the output of the two regulators is that they will not share current evenly. Once unbalanced, the two regulators start a "tug of war" for dominance as one will try to regulate the other. There are some workarounds to this where you add external circuitry to balance the load between the two regulators such as this  app note, but we do not support any specific solution for bq25570. Tying the BAT pins is not an issue as the there is an internal FET separating the pin from the power converter.

    Thanks,

    Ricardo

  • 0 in reply to Ricardo
    Prodigy 40 points

    Thank you, Ricardo! That gives me a starting point to read up on.