Regarding the configuration of SPV1050.

[Prajnyajit]

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.

[Prajnyajit]

Thanks Peter. I got it. I have posted a query related to STEVAL-ISV020V1. Can I directly use it for charging supercapacitor? Can you help me in that ?​

[Peter BENSCH · Accepted solution]

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

[Prajnyajit]

Hi, Peter!

Thank you for your response. I solved it as per my conditions and found R1= 6.1MOhm, R2 = 0.6 MOhm, R3 = 2.5 MOhm, R4 = 6.34 MOhm, R5= 2.5 MOhm, R6 = 6.15 MOhm. If I connect the supercapacitor to the Batt pin then can you tell me what will be the range of voltage we can get ? The minimum voltage you have told that it will be 2.6V then what will be the maximum voltage through the Batt pin?

If I want to use LDO1 to provide a constant 3.3 V to my load then can I use it when the super capacitor voltage is between 1.8 - 3 V?

[Peter BENSCH]

Great!

BATT pin: The maximum voltage, identical to your battery/supercap voltage, is 5.3V (datasheet, table 4, Veoc).

LDO1: of course, an LDO can only reduce an input voltage by at least the dropout voltage. To generate a higher voltage, you need a boost converter (inductive or charge pump based).

Regards

/Peter

[Prajnyajit]

I appreciate your quick response, Peter! Just little more help will be enough.

1. I am making it more clear, that I think generating 3.3V, LDO 2 will be suitable instead of LDO1 if I am not wrong. But in my condition, as I said, it should provide a constant voltage of 3.3V for supercapacitor output voltage in the range 1.8V - 3V, will it work? Or else I have to use a separate boost converter/charge pump to do this job?
2. We have solved the resisters, now what about the capacitors and inductors values to charge a supercapacitor according to my condition? Will they be sam,e as the schematic attached in this thread or different? If so what values should they have?
3. We have solved the registers, but regarding STEVAL-ISV020V1, I think the registers are fixed on the board. So according to my condition (to charge a supercapacitor as we have solved using different equations) should I have to design it new on a PCB? I think STEVAL-ISV020V1 directly can't solve my purpose as it is not satisfying the equations we have solved as per my conditions, isn't it?

[Peter BENSCH]

1. Yes, you have to use a separate boost converter or charge pump to create a voltage bigger than the input, e.g. 1.8-3V --> 3.3V
2. The inductor should be fine, as stated before you could try to increase its value from 22µH to 33...100µH. In the case of the capacitors, only the input capacitor at the solar panel (C1 in STEVAL-ISV020V) should be rechecked, which can be determined with equation 8 and 9. Figure21 shows the influence of the capacity on the charging voltage.
3. It depends on how much systems you want to build: for test purposes or just a single system it should be fine to replace the original resistors by the new ones.

Good luck!

/Peter

[Prajnyajit]

Refer to this ckt diagram.

[Prajnyajit]

Are you telling me that I can replace the SMD registers on STEVAL-ISV020V1 with the obtained registers value so as capacitors and inductors?

[Peter BENSCH]

It is of course not that easy to replace the SMD components, but a workable solution if you can.

Alternatively, you can also build your own board, whereby you have to consider possible leakage currents due to the high resistance values.

Regards

/Peter

[Prajnyajit]

Thank you, Peter! Thanks for the help. I appreciate your responses and will contact you further if I get any doubt.