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I have the TI bq25601 and it has a pin called SYS. The datasheet says this:

Converter output connection point. The internal current sensing network is connected between SYS and BAT. Connect a 20 µF capacitor close to the SYS pin

But I don't really understand what it does.

Can somebody explain it to me?

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  • \$\begingroup\$ For high efficiency, the chip regulates charging voltage using a buck-converter topology, which requires an external inductor and capacitor for it's LC filter. The chip also contains circuitry to monitor charge current. Since the LC filter is external, it's output must be fed back into the chip in order for the current to flow trough the current sense circuit. This is done trough the SYS pin. \$\endgroup\$ Aug 4 at 18:54
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    \$\begingroup\$ It's just the output of the converter, isn't it? \$\endgroup\$ Aug 4 at 18:55
  • \$\begingroup\$ yep, it's the output. @Patrick. Now the question becomes: if you don't understand what SYS is, what do you think is the purpose of the bq25601? \$\endgroup\$ Aug 4 at 19:09
  • \$\begingroup\$ @Unimportant Thanks for your answer. I do understand this now, but I got another question. I now need to connect a LC Filter. How do I choose the right capacitor and coil values. I didnt found any formulas for those values. \$\endgroup\$
    – Patrick
    Aug 4 at 19:11
  • \$\begingroup\$ @MarcusMüller A Charging IC which is controllable via I2C. \$\endgroup\$
    – Patrick
    Aug 4 at 19:13
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SYS pin is system load net of a system.

Look at the block diagram on p.15 of the datasheet and fig.28 . When battery is powers the system, current flows out of the SYS pin. When the external power is connected, the current flows into the SYS pin.

[This description is for this particular IC. It can vary from one charger IC to another.]

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