SPV1050 Res and Cap Equations Help

Question

Posted on October 31, 2017 at 00:52Hi,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 = 630mVVmpp = 501mVMany thanks.David.

Smith.David · Answer

Posted on October 31, 2017 at 01:22Desired UVP = 2.75V with EOC 4.2VR4uvp =  6.8MR5eoc = 0.75MR6out = 3MBandgap internally = 1.23VEquation 1Bandgap = UVP * ( R5+R6 ) / (R4 + R5 + R6)= 2.75V * 3.75 / 10.55= 10.31 / 10.55= 0.90Equation 2 Bandgap = EOC * R6  / (R4 + R5 + R6 )= 4.2V * 3 / 10.55= 10.31 / 10.55= 1.19Equation 3 R4+R5+R6 = 10.55M  which is in between 10M and 20M as required by datasheet.

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