AN3392 Datasheet, PDF (34/57 Pages) STMicroelectronics – The SPV1020 is a monolithic DC-DC boost converter designed

External component selection
AN3392
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 (V_{out_rp_max}):
Equation 20
C_out
≥
---------------------^I-^s---^c---------------------
V_{out_rp-max} ⋅ F_SW
It is suggested to split the capacitance into four capacitors, each to be connected to each of
the four V_OUT 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 V_{OUT_MAX} is the maximum output voltage at the load, then R3 and R4 must be selected
according to the following rule:
Equation 21
R_-----3_{-- = -}^V_----o_--u_---t_-__---m_----a_--x_{- – 1}
R4 1.00
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 V_{OUT_SNS}, maximum power dissipation in
the series connection of R3 and R4 is:
Equation 22
P_{vout_sns}
=
(_---V_{----o---u---t--_--m----a---x---})²
R3 + R4
Empirically, R3 and R4 should be selected according to:
Equation 23
P_{vout_sns} « 1%(V_{out_max} ⋅ I_{out_max})
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