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LT3652 voltage divider


I am looking at LT3652 datasheet, and I see the Battery Floating Voltage is set with a voltage divider between pins BAT and VFB. 2 equations are provided to calculate the resistor values (page 14, equations for Rfb1 and Rfb2). The 2 equations on page 14 are RFB1 = (VBAT(FLT) • 2.5 • 10^5)/3.3 and RFB2 = (RFB1 • (2.5 • 105))/(RFB1 - (2.5 • 10^5))

I am trying to use these equations to match the typical application example on page 26, where rfb1 is 309k and rfb2 is 100k, but I can't satisfy the 2 equations. The only thing I notice is that with a voltage of 13.5v applied to that voltage divider, output is 3.3v. 

Could you please help me to clarify how these values relate to the equations provided?


Parents Reply
  • Thank you for your answer Markus. I'm actually looking to implement LT3652 for a li-ion battery solar charge controller (7.4v 2S battery). I though the equations under the "Battery Float Voltage Programming" would apply for any situation. I see on page 22 there is an example for "2-Cell Li-Ion Charger (8.3V at 2A)", but this one uses an AC adapter input.

    Do you have any suggestions about which approach to take to implement this charge controller? I was able to find an example in here:

    that suggests that for a 2S LiPo battery, with a charge voltage of 8.4v, rfb1 should be 154k and rfb2 100k. I want to corroborate this values, but I haven't been able to match them to any of the equations of the datasheet.