AN4397 datasheet(12/19 Pages) STMICROELECTRONICS

12 / 19 page

Component selection

AN4397

12/19

DocID025515 Rev 1

Component selection

This section describes the application rules to be followed for properly selecting the

components around the SPV1050 device.

4.1

MPPT setting

The “Maximum Power Point” (MPP) is set through the input resistor partitioning R1, R2 and

R3.

As a preliminary rule, the voltage on the MPP pin (VMPP), which depends on the voltage

supplied by the selected source (VIN), must be ≤ VUVP (which is set by the output resistor

partitioning R3, R4, R5).

So, the following equation:

Equation 1

can be rewritten as follows:

Equation 2

VOC(MAX) stands for the maximum voltage that the source can supply (open circuit voltage).

Further, the MPPRATIO = VMPP_SET / VOC is set by the following equation:

Equation 3

For the PV panels the VMP is typically in the range between 70% and 80% of VOC.

Finally, the leakage on the input resistor partitioning must be negligible, hence typically it

must be:

Equation 4

10 M

 ≤ R1 + R2 + R3 ≤ 20 M

VMPP

VIN

R2 R3

R1 R2 R3

------------------------------------ VUVP



VUVP VOC MAX



R2 R3

R1 R2 R3

------------------------------------



VMPP SET

VINx

R1 R2 R3

------------------------------------

MPPRATIO VOC



VINx

R1 R2 R3

------------------------------------

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