AN3392 datasheet(32/57 Pages) STMICROELECTRONICS

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External component selection

AN3392

32/57

Doc ID 018749 Rev 1

Low ESR capacitors are a good choice to increase the entire system efficiency.

10.4

Internal voltage rail capacitors

C7 is a tank capacitor used to guarantee the voltage level (5 V) of the internal SPV1020

voltage regulator.

The suggested value is 470 nF and is not application dependent.

The voltage range is the same as for the boost capacitors. Maximum voltage must be higher

than 5 V.

Low ESR capacitors are recommended in order to increase the entire system efficiency.

10.5

Input voltage capacitors

C5 is the input capacitance added at the input to reduce the voltage ripple.

The maximum voltage of this capacitor is dependent upon the input source (typically

between 25 V and 50 V).

Low-ESR capacitors are recommended in order to increase the whole system efficiency.

Suggested minimum input capacitance is 2 µF.

In order to reduce the ESR effect, it is suggested to split the input capacitance into 2

capacitors connected in parallel.

Another capacitor (C11) is connected to the supply input pin of the SPV1020 (Vin). Its role is

to stabilize the voltage as much as possible on this pin which may be affected by the ripple

of the PV panel voltage.

Considering the maximum current (Isc) provided by the PV panel connected at the input, the

following formula can be used to select the proper capacitance value (Cin) for a specified

maximum input voltage ripple (Vin_rp_max):

Equation 14

10.6

Input voltage partitioning

The input voltage must be scaled to the reference voltage (1.25 V) of the ADC integrated in

the SPV1020.

R1 and R2 are the 2 resistors used for partitioning the input voltage.

When the the open circuit voltage (Voc) of the PV panel is known, the said R1 and R2 must

be selected according to the following rule:

Equation 15

Cin

in_rp_max

⋅

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

≥

--------

1.25

-----------

–

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