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I am testing my circuit of a single charger for a dual battery system. For that, I am using the LTC4001 combined with the LTC4415 (just as the picture below.)

I don't understand the reason for the 50k resistor. Similarly, I do not get why the 1.5k voltage divider goes to BATSENS.

I understand that the charger needs a BATSENS to know the status of the load, but this configuration makes it so that when BAT1 is disconnectedsome voltage is induced in LOAD1 coming from BAT2. This raises some unexpected behavior in my LOAD1. Is the 50K resistor really necessary? Other dual OR diodes do not consider it.

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  • \$\begingroup\$ One of those resistors doesn't go to BATSENS so, please correct your question. \$\endgroup\$
    – Andy aka
    Dec 17, 2021 at 10:50
  • \$\begingroup\$ probably it needs a DC path to make the batsense circuitry work correctly. If it's not clear from the datasheet ask Linear/Analog Devices, they are helpful usually \$\endgroup\$
    – Lorenzo Marcantonio
    Dec 17, 2021 at 12:18

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The purpose of the 1.5k resistor divider is to provide status of both batteries to the charger chip using only one sense input. Since the charger chip does not have dual battery sense inputs, then it needs a general status of both batteries. If BATSENS was connected only to one of the battery + terminals, then the other battery wouldn't be able to affect the charge cycle when low.

Ideally, both batteries are at the same charge and reflect the correct BATSENSE feedback, but if not then the divider simply takes half of the difference between the batteries as the feedback.

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  • \$\begingroup\$ Thanks, but what about the issue of having the induction of VBAT1 over LOAD2 when VBAT2 is disconnected? Any idea to change this? \$\endgroup\$
    – Wladimir Dlc R
    Dec 18, 2021 at 18:56
  • \$\begingroup\$ This single-charger chip design is a compromise in performance vs. component count, not perfect solution. I think this circuit is best for applications that don't remove the batteries or where the loads will not operate on charge current alone, or no load (just a charger). My guess is the 50K resistor improves the automatic recharge cycle when both batteries are at different levels. \$\endgroup\$
    – icodeplenty
    Dec 18, 2021 at 23:28
  • \$\begingroup\$ To reduce the effects of BAT2 into LOAD1 when BAT1 is removed, just increase the divider resistor values, however, there will always be voltage coming from the charger chip for any real load. \$\endgroup\$
    – icodeplenty
    Dec 18, 2021 at 23:36

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