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I am using the HP4059 charger to charge a 35 mAh battery. Here is my schematic: enter image description here

I have placed a 3 kΩ resistor R1 (charging current of 33.3 mA). If there is no load on VBAT, everything works fine, and the VBAT voltage is 4.2 V. However, if I connect a load to VBAT < 850 Ω, the VBAT voltage drops to 1.6 V. If I reduce the R1 resistance to 2.1 kΩ, the situation is corrected (VBAT voltage of 4.2 V), but I cannot use this resistor as I am afraid of damaging the battery since the charging current will become 47 mA. What can I try to fix the situation?

winny
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Максим Захаров
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  • "load on VBAT" - that pin is purely for providing charging current to the battery. There should not be any load on it. The device is unable to tell what's going into the battery and what's going to something else. – Finbarr Aug 18 '23 at 12:20
  • Thank you for your response. I do not understand how to achieve this because the LDO is connected to the VBAT output, and the LDO powers the processor, which consumes current (proportional to a resistor <850Ohm) during startup. – Максим Захаров Aug 18 '23 at 19:25
  • You can either make sure no load is taken from the circuit while charging the battery or provide a separate power path for the load. – Finbarr Aug 19 '23 at 12:31

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