SPV1050 datasheet(24/36 Pages) STMICROELECTRONICS

24 / 36 page

Functional description

SPV1050

24/36

DocID025569 Rev 4

6.4

MPPT setting

When the MPPT feature is enabled, the SPV1050 device sets its working point such that VIN

= VMPP. In fact, VMPP is a fraction of the open circuit voltage VOC of the harvesting source.

Figure 19. MPPT setup circuitry

The maximum power point is set through the input resistor partitioning R1, R2 and R3.

First of all, set the total input resistance (R1 + R2 + R3) considering the maximum

acceptable leakage current (ILEAKAGE):

Equation 4

ILEAKAGE = VOC / (R1 + R2 + R3)

Typically, assuming 10 M

≤ R1 + R2 + R3 ≤ 20 M, the leakage on the input resistor

partitioning can be considered as negligible.

Then set the R2 + R3 selecting the minimum between the results of equations 5 and 6 which

consider that the voltage on the MPP pin must be lower than the minimum VUVP (VUVP(min)

= 2.2 V) and the energy balance on the inductor even at very low input power (see details in

Appendix A, Application tips), respectively:

Equation 5

R2 + R3 ≤ (R1 + R2 + R3) * VUVP(min) / VOC

Equation 6

R2 + R3 ≤ 51 * (R1 + R2 + R3) * VMPP(min) / VEOC

Finally, set the R3 considering the MPPRATIO (in case of PV panels MPPRATIO = VMP / VOC):

Equation 7

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