Regarding the configuration of SPV1050.

Prajnyajit · ‎2021-07-30

Hi,

I have SPV1050 and want to use it with a solar cell. The parameters of the solar cell are listed below.

Voc = 6.91 V (Open circuit voltage)

Isc = 58.60 mA (Short circuit current)

Pout = 307.30 mW ( Maximum deliverable power)

Vload = 5.58 V (Output voltage at load condition)

Iload = 55.10 mA (Current output at load condition)

Please help me configure the peripherals of SPV1050 like the connection diagram which includes the resister and inductor and capacitor values which should be connected at which pins. I have an evaluation board of it too. I have gone through the manual but couldn't find it helpful enough.

Peter BENSCH · ‎2021-08-10

Yes, the STEVAL-ISV020V1 can be used for supercapacitors, but of course it is current-limited.

MPPT only works from an input voltage of 2.6V (data sheet, section 6.3) if the integrated DC-DC converter is working. If you connect the single supercap directly to pin STORE, it creates a short circuit so that MPPT can practically never work: "In case of buck-boost configuration, once the harvested source is connected, the IN_HV

and STORE pins will be internally shorted until VSTORE < 2.6 V." Theoretically, the capacitor on pin STORE could be used as a buffer, the charge of which is periodically pushed into the supercap (see data sheet, section 6.1), but then MPPT will not really work properly.

In your case, it probably makes the most sense to connect the supercap to BATT via a resistor of ≥37.5 ohms. This resistor guarantees a minimum voltage of 2.6V at BATT, even when the supercap is completely discharged. This means that the DC-DC converter can work and therefore MPPT, too.

When the supercap is charged, it also supplies LDO1 and LDO2 backwards via the pass transistor. If you use it and want to use the maximum current, you could insert a Schottky diode parallel to the series resistor of the supercap (anode on pin BATT).

Finally set the values of R4, R5, R6 according to the equations 1...3 of the datasheet (section 6.1), with

VBG=1.23V
VUVP=2.2V
VEOC=your target voltage, e.g. 3.2V

and use equations 4...7 to set MPPT:

eq4: e.g. R1+R2+R3 = 10 Mohms
eq5: R2+R3 ≤ 10 Mohms * 2.2V/6.91V ≤ 3.18 Mohms, say 3.1 Mohms
eq6: will be much bigger than the result of eq5, so ignore
eq7: set R2/R3 according to your required MPPratio, e.g. 0.7...0.8 (please read MPPratio=VMP/VOC as MPPratio=VMPP/VOC)

Regards

/Peter

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Prajnyajit · ‎2021-07-30

I want to charge a supercapacitor with this solar cell. The supercapacitor is 500 F and its rated voltage is 2.7 VDC and it can be charged with 3.2 V DC.

Peter BENSCH · ‎2021-08-09

Are you sure the max voltage on your 500F super capacitor is 3.2V and not 2.3V at high temperature?

The SPV1050 delivers a maximum charging current of 70 mA. Did you know that charging of 500F from 0V to 3.2V with 70mA can take up to 6:20 hours?

Regards

/Peter

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Prajnyajit · ‎2021-08-09

Thanks Peter for your response to my query!

Yes, I know. I modeled it using mathematics and I am sure it will take 11-13 hours to charge it. My application is quiet fit for this thing too. So this won't make any issue to me. Regarding the charging voltage, what I know in general is the temperature in my application will be around 35 degree C. Can you help me in the configuration of the demo board ?

Regards,

Prajnyajit

Prajnyajit · ‎2021-08-09

The supercapacitor maximum output voltage is 3V while the nominal voltage is 2.7V. so it should be charged with 3V - 3.2V (charging voltage) maximum.

Peter BENSCH · ‎2021-08-09

Which board do you have on the table right now?

Unfortunately, we have not yet tried to charge a supercap directly with the SPV1050, so we cannot make any recommendations.

However, you should run the SPV1050 in buck-boost mode.

Since a supercap does not require an undervoltage protection, you could connect pin UVP to ground instead of R4/R5. According to the datasheet, equation 2 and 3, R6 should be set to e.g. 1.23V*10Mohms/3.2V = 3.9 Mohms, in this case, R4 + R5 can be combined to a single resistor of 6.1 MOhm (or 3.9M+2.2M). Both values multiplied by the appropriate factor if a total resistance of 20 Mohms is used instead of the recommended min value of 10 Mohms.

It is questionable whether MPPT will work when the UVP is disabled, so it will likely have to be turned off.

On the other hand, UVP can make sense because the boost converter that is likely to follow also has a minimum voltage from which it works, right?

The inductor value of 22µH should be fine, you could also increase its value to e.g. 47...100µH. Please pay attention to its saturation current, which should be higher than the peak current of 140mA.

Regards

/Peter

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Prajnyajit · ‎2021-08-09

On the datasheet itself, it is mentioned in the application section that it can be used to charge a supercapacitor. So why it is so questionable to be used with supercapacitors? I want to use the MPPT at every cost. Please suggest me accordingly. I have an evaluation kit (Development board) with me. Here the values of these resistances are fixed I think, so how I will set them? Please tell me the connection procedure for this particular board. I'm unable to operate this board. Please let me know the connection procedure or provide me training video/ operation manual or any such material to operate this particular board.

Prajnyajit · ‎2021-08-09

I'm unable to operate this board. Please let me know the connection procedure or provide me training video/ operation manual or any such material to operate this particular board.

Prajnyajit · ‎2021-08-09

For safe operation, VEOC should be 3V (not 3.2 V) and the Vupv should be 2.2 V. How to set this thing on the development board STEVAL-ISV019V1?
In this condition and with the solar cell specification it will operate in buck-boost mode. I agree with this. But how to select this mode on STEVAL-ISV019V1 or it will be auto-selected?
Tell me how can I set MPPT on STEVAL-ISV019V1?
In my case I think my supercapacitor will be connected to CN2 pin 1 and Pin 2, isn't it?
PV will be connected to CN1, Pin1 & Pin2, isn't it?

As long as I use STEVAL-ISV019V1, this configuration is enough for my application or not? Please advise me of any further connection-related thing, if I have missed any which is necessary for it.

For simplification and better understanding, I am attaching the circuit diagram and you can mark the connection diagram in the picture itself.

Peter BENSCH · ‎2021-08-09

The STEVAL-ISV019V1 cannot be used for your application due to fixed connections for boost operation:

IN_LV (16) connected to the input voltage
IN_HV (20) is connected to GND

You should use the STEVAL-ISV020V1 (Buck-Boost) instead.

Regards

/Peter

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