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SM72445EVM

Gerry Kurz
Intellectual 685 points
Other Parts Discussed in Thread: SM72445

Hi,

I am evaluating the SM72445 to include in a new design for one client and to replace some Linear Tech parts in some designs for another client.

I have a SM72445 EVM board and I have hooked it up to a solar panel simulator and and electronic load as per the evm user guide and it seems to work as expected.

I now need to test it with a 12 V sealed lead acid battery.

When I hook up the battery to the output with the simulator off, the battery voltage appears on the input. This should not be happening as far a I can tell.

Also when I run the simulator, the SM72445 only seems to only run in panel mode and not in MPP tracking mode.

Can I get some expedited help with this?

Thanks

  • 0
    Intellectual 685 points
    It seems to be working (at least in buck mode) now but I am still wondering why the output voltage shows up at the input.
  • 0 in reply to Gerry Kurz
    TI__Intellectual 1775 points

    Hello,

    The SM72445EVM is not designed to be connected to a battery on the output but rather to a solar panel string connected to an inverter or alternatively, to a resistive load.

    It was designed as a solar panel optimizer to reduce the impact of shade or string imbalance in PV array applications. The SM72445 and EVM is designed to start in "Panel Mode" and be transparent to a solar array. It is designed to begin operation after the inverter begins pulling current from the PV string(s) by sensing that current drawn from the solar panel. There is a delay programmed into the IC to let the system (mostly driven by the inverter) settle into a steady state before beginning MPPT operation. Although that delay could be turned to 0 seconds by setting A6 to 3.44V (SM72445 datasheet, Table 2, page 9) by modifying the resistor divider.

    Therefore if connected to a battery, the converter will likely run into a panel mode and the battery voltage will be displayed at the input until enough current is passing through AND the timer has elapsed.

    With a battery there could be issue with this setup due to the possibility of reverse current flowing into the solar panel. Operation in BOOST mode might not work since the system needs current flowing out of the panel into the output before it can properly perform MPPT.

    Best Regards,

    Florent

  • 0 in reply to Florent Boico
    Intellectual 685 points

    Hi Florent,

    Thanks for your response.

    I understand the problem of getting the part to operate in boost mode when connected to a battery however I do not see why it would not work fine charging a battery directly in buck mode. If I were to choose to do this, and to ensure that the part always operated in buck mode, could I eliminate two of the output fets?

    Also my question about the battery voltage showing up on the input is referring the condition where there is no panel connected and the part should be powered down on the evm. A battery is connected to the output however there should be no current flow from the battery back to the panel if the SM72445 is powered down. Yet this seems to be happening. I was hoping you could shed some light on this condition.

    Gerry

  • 0 in reply to Gerry Kurz
    Intellectual 685 points
    How do I get more support for this part and it's evaluation module? Is there more documentation?
    What are the ADC offsets and offset tempco's for the SM72445?
    How are the ADC offset registers used?