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SM72445 with limited duty cyle

Luis Kawahara
Prodigy 90 points
Other Parts Discussed in Thread: SM72445, SM72295

Hi,

I'm trying to make a scap charger with the SM72445, but it seems my duty cycle is being limited when operating in Boost mode. It looks like the limit is about 15%.

I'm not using I2C, so my setting are the following:

A0 = 5V - I'm using the SM72295 to limit the output voltage

A2 = 2.19V - Use H-bridge for PM mode

A4 = 5V - Current limit disabled

A6 = 5V - This is where I have some questions... I want my Iout_th to be 0A. In other words, I want my circuit to ALWAYS enter MPPT mode, because sometimes my load will be 0A, but I need the Vout to be at the value that I set.

Some additional informations:

- The voltage at the VOUT pin on my SM72445 is far from reaching the 5V. Around 3.4V;

- The PV module have a MPPT voltage of 17V, and the voltage at the AVIN pin is set to be 4V when PV is 21V;

- The current sense gain is set to 1V/A, and the highest current that my PV can achieve is 1.2A;

- The reset pint is always high. 

If anyone can help me, please do. I'm getting desperate!

If more information is needed, please ask.

Thanks!

  • 0
    Prodigy 90 points

    I´ve had some progress.

    My circuit does work, but my supercapacitor branch voltage need to be lower than the my solar panel voltage for it to work. That´s probably because of the blocking diode. When the supercapacitor voltage is lower than the output, there is no current, so the MPPT won´t start.

    Is there a way to bypass this? I tried using a resistor, but had no success... If I take the blocking diode, the circuit keeps running when I unplug my solar panel.

    My current settings are:

    A0 - 5V

    A2 - 2.19V

    A4 - 5V

    A6 - 1.56V

    Thanks