Load Current Sharing of Iin and Ibat?

Zack,

My custom board has been performing flawlessly for the past ~10 day. Nice!

However, I am confused about some of the readings of input current, battery current, and load current. From what I am seeing from my telemetry data, when the sun first comes up and the solar panel is not yet able to provide much current, it APPEARS as though the load current is being partially supplied by the solar panel, and partially supplied by the battery. Take a look at the readings below. FYI, Pout is derived from Vout, and Iout (load) is derived from Pout/Vout. However, Iin and Ibat are actual telemetry readings.

Also note that when this happens (low solar input) that Vout is always ~.5V below Vin, and Vbat is always about the same as Vin. Does this make sense?

Below is a graph of Vout showing the "dips" with low sun.

Thoughts and guidance appreciated.

  • 0
    •  Analog Employees 
    on Apr 6, 2020 4:20 PM

    Hi Mike,

    This is an LTC4162 circuit, right?

    Consider the external PowerPath FETs to be a dumb diode-or circuit. It will basically just pass the higher of the two sources to the load. If your input voltage drops to near the battery voltage, the source may switch over to the battery.

    The two sources will not cleanly share current. Rather, the FETs will turn on-off as one source starts supplying current and droops below the other source. This may cause the FETs to go into a "chattering" state while the VIN and battery voltages are very close to each other. This may effectively cause a small drop on Vout as both FETs may spend a short time off.

    I would consider this normal operation if this is the case. Some operation like this may be unavoidable when operating from a solar panel given the inconsistency of input power.

    Regards,

    Zack

  • I would consider this normal operation if this is the case. Some operation like this may be unavoidable when operating from a solar panel given the inconsistency of input power.

    I consider it useful since the under powered solar panel is still preventing the battery from having to supply the entire load.

    Thanks for the input. Great chip!