SPV1050 Res and Cap Equations Help

[Smith.David]

Posted on October 31, 2017 at 00:52

Hi,

Please see schema below.

With this circuit the cells in series are creating ~ 0.82V in office lighting.

LDO2 output is only 0.5v.  This does not seem right. :)

Can anyone at ST help with correct selection of R1-6 suitable for two KXOB22-12X1 in series charging a 3.7v 100mAh LiPo. One too many equations in the data sheet for me!

http://ixapps.ixys.com/datasheet/20110302-kxob22-12x1-data-sheet.pdf

 

Voc = 630mV

Vmpp = 501mV

Many thanks.David.

[Smith.David]

Posted on October 31, 2017 at 01:22

Desired UVP = 2.75V with EOC 4.2V

R4uvp =  6.8M

R5eoc = 0.75M

R6out = 3M

Bandgap internally = 1.23V

Equation 1

Bandgap = UVP * ( R5+R6 ) / (R4 + R5 + R6)

= 2.75V * 3.75 / 10.55

= 10.31 / 10.55

= 0.90

Equation 2

Bandgap = EOC * R6  / (R4 + R5 + R6 )

= 4.2V * 3 / 10.55

= 10.31 / 10.55

= 1.19

Equation 3

R4+R5+R6 = 10.55M  which is in between 10M and 20M as required by datasheet.