External component selection

AN3319

16/25

DocID18265 Rev 8

According to the maximum current (I

SC

) provided by the PV panel connected at the input,

the following formula can be used to select the proper capacitance value (C

OUT

) for a

specified maximum output voltage ripple (V

OUT_rp_max

):

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

SPV1040 can support up to 5.2 V, so the suggested maximum voltage for these capacitors

is 10 V.

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

Output voltage partitioning

R

1

and R

2

are the two resistors used for partitioning the output voltage.

The said V

OUT_max

the maximum output voltage of the battery, R

1

and R

2

must be selected

according to the following rule:

Also, in order to optimize the efficiency of the whole system, when selecting R

1

and R

2

, their

power dissipation must be taken into account.

Assuming a negligible current flowing into the V

CTRL

pin, maximum power dissipation on the

series R

1

+R

2

is:

As an empirical rule, R

1

and R

2

should be selected to get:

Note:

Output voltage sensing capacitor

C

2

is placed in parallel to R

2

and as close as possible to the V

CTRL

pin.

Its role is to reject the noise on the voltage sensed by the V

CTRL

pin.

Capacitance value depends on the time constant resulting from R

2

(

τ

OUT

= C

2

*R

1

//R

2

) and

from the system switching frequency (100 kHz), as follows:

C

OU T

I

SC

F

SW

V

⋅

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

≥

OUT_rp_max

R

1

R

2

-------

V

OUT

1.25

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

=

_max

-1

P

V

OUT m ax

R

1

R

2

+

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

=

_

P

V C TR Lsns

0.01

V

OU T m a x

I

OU T m ax

⋅

()

⋅

«

_

_

_

ssw

F

1

10

out

∗

≅

τ

2

1

ssw

2

R

//

R

1

*

F

1

*

10

C

≅