AN3392 datasheet(34/57 Pages) STMICROELECTRONICS

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External component selection

AN3392

34/57

Doc ID 018749 Rev 1

Critical parameters for capacitors are: capacitance, maximum voltage and ESR.

Maximum voltage of this capacitor is strictly dependent upon the output voltage range. The

SPV1020 can support up to 40 V. The minimum suggested voltage for these capacitors is

50 V.

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

The suggested minimum output capacitance is 28 µF. In the case of series connection (see

Appendix B: SPV1020 parallel and series connection), it is suggested to increase the output

capacitance up to 100 µF.

In order to reduce the ESR effect it is suggested to split the output capacitance into three

capacitors connected in parallel.

In accordance with the maximum current (Isc) provided by the PV panel connected at the

input, the following formula can be used in order to select the proper capacitance value

(Cout) for a specified maximum output voltage ripple (Vout_rp_max):

Equation 20

It is suggested to split the capacitance into four capacitors, each to be connected to each of

the four VOUT pins of the SPV1020. This helps to balance the impedance of the four tracks.

10.9

Output voltage partitioning

R3 and R4 are the two resistors used for partitioning the output voltage.

If VOUT_MAX is the maximum output voltage at the load, then R3 and R4 must be selected

according to the following rule:

Equation 21

Also, in order to optimize the efficiency of the entire system, when selecting R3 and R4, their

power dissipation must be taken into account.

Assuming negligible current flowing through pin VOUT_SNS, maximum power dissipation in

the series connection of R3 and R4 is:

Equation 22

Empirically, R3 and R4 should be selected according to:

Equation 23

out

out_rp-max

⋅

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

≥

--------

out_max

1.00

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

–

vout_sns

out_max

()

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

vout_sns

1% V

out_max

⋅

()

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