AN4394 datasheet(11/18 Pages) STMICROELECTRONICS

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AN4394

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

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

If the electrical characteristics of the selected source and battery are such that

VOC(MAX) ≤ VUVP, the resistor R1 can be simply replaced by a short-circuit. Consequently,

only R2 and R3 have to be selected for a proper setting of MPPRATIO.

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

For the TEG the VMPP_SET is equals to 50% of VOC, so the selection is R1 = 0 and R2 = R3.

VMPP

VIN

R2 R3

R1 R2 R3

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



VUVP VOC MAX



R2 R3

R1 R2 R3

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



VMPP SET

VIN

R1 R2 R3

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

MPPRATIO VOC



R1 R2 R3

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

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