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I am looking for circuits used to measure or monitor the current charging of a battery (Li-Ion or NiMH), microchip has proposed the following circuit:enter image description here

My concerne is about the selected circuit in RED

I did not understand how does this ciruict works! *Why have we used R24=1.2M? Especially in case we remove R21 (As it is noted by DNP)

*What is the contribution of R16, C12 and R18 in measuring the current flowing through a parallel resistors R4 and R5

*What about C15, is it used as a filter or just for optimization?

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  • \$\begingroup\$ Since the circuit is used to measure a variable current during the charging process of a battery, does R18 and C12 constitute a snubber to supress spikes ?? \$\endgroup\$
    – learn design
    Commented Nov 6, 2019 at 20:58

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I did not understand how does this ciruict works! *Why have we used R24=1.2M? Especially in case we remove R21 (As it is noted by DNP)

Recall, that this is circuit is both a battery charger and power supply, so the battery current is bi-directional. When operating as a power supply the battery is discharging and the current-shunt output potential is below PGND.

The role of R24 is to bias the output of the current shunt above ground on this single supply design. Resistors R24 and R16 form a voltage divider that bias the current shunts potential up by approximately 200 mV (if I am reading the supply rail correctly as 5VDC).

The remaining components would be selected for filtering and loop compensation of the constant current control loop.

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  • \$\begingroup\$ In case of a power supply (the battery is discharging), is the discharging current controlled ? I think when the battery used as a power supply, the whole circuit is used as a buck converter and only the voltage loop takes control. \$\endgroup\$
    – learn design
    Commented Dec 5, 2019 at 5:20
  • \$\begingroup\$ Can you tell me why the two pins of U4:A are biased differently? the positive pin is taken up by 200mv and the negative one is taken up by 175mv. \$\endgroup\$
    – learn design
    Commented Dec 15, 2019 at 21:08

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