AN3392 datasheet(30/57 Pages) STMICROELECTRONICS

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External component selection

AN3392

30/57

Doc ID 018749 Rev 1

10.1

Power and thermal considerations

The SPV1020 performance is strongly impacted by the power capability of the PowerSSO-

36 package, as well as the application board. According to the technical note TN0054,

RTH(j-a) of the PowerSSO-36 can be decreased to 10 °C/W if the package is soldered onto a

“2s2p” multi-layer board with thermal vias and a metal plate for an external heatsink.

Starting from this value, it is possible to calculate the PMAX.

Equation 6

Equation 7

The SPV1020 efficiency (

η) is ≥ 98%; the thermal shutdown threshold is 140 °C;

typical ambient temperature (TAMB) for a photovoltaic application is 85 °C.

Calculating maximum power dissipation Pd:

Equation 8

Equation 9

If the package is soldered onto a “2s2p” multi-layer board with thermal vias, the RTH(j-a) is

20 °C/W and then PMAX is 138 W. (PCB with 4 layers: 2 soldered layers, top and bottom,

and 2 power layers (inner layers for power dissipation).

10.2

Inductor selection

Inductor selection is a critical element for this application.

Inductor selection must take into account the following application conditions:

●

Maximum input current (i.e. Imp and Isc of the PV panel)

●

Maximum input voltage (i.e. Vmp and Voc of the panel)

●

Overcurrent threshold of the SPV1020

●

Maximum duty cycle, according to maximum output voltage

Input current from the PV panel is split between the 4 inductors of each branch, so:

Equation 10

AMB

TH j

–

()

⋅

–

() P

MAX

⋅

J TAMB

–

TH j

–

()

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

5.5W

MAX

–

()

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

275W

Lx rms

()

--------

------

≅

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