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I need a Lithium ion battery for a project.

In many places, I have searched and there seem to be 2 different voltages for the Li-ion battery. One is 3.7V and one is 4.2V. In someplaces, it is said that the Li-ion battery is a standard one. Typical battery voltage i 3.7V and maximum battery voltage is 4.2V. In other places, it is mentioned that 3.7V and 4.2V lithium batteries are two different voltage level batteries.

Can someone please confirm which one is correct?

Also, when I need to charge this battery (3.7V or 4.2V), can someone tell me the safe range of the battery charging input voltage (What input voltage at Vdd pin?) that I need to give to this Charge controller IC? What input for 3.7V and What input voltage for 4.2V? Also, please tell me whether I use the maximum input vdd voltage of 6V for charging these batteries using the above charger controller.

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  • \$\begingroup\$ Read the datasheet for the battery you have. I have seen li-ions rated for anything in the rang 2.5-3.2V as min voltage (fully discharged), and anything from 4-4.5V maximum votlage (fully charged) though 3.7V seems to always be quoted as nominal. \$\endgroup\$
    – Puffafish
    Feb 2, 2023 at 10:28
  • \$\begingroup\$ As for charging voltage, again check the datasheet. But that also depends on how you control the charging of it (and which saftey regulations you need to comply to). If you're using constant-current/constant-voltage, then you constant-voltage will want to be between 0.2 and 0.5V above fully charged votlage for the battery. \$\endgroup\$
    – Puffafish
    Feb 2, 2023 at 10:31
  • \$\begingroup\$ Inflating numbers seems to be an on-going problem across all fields in today's society. In the good old days, the nominal voltage was always used. Recently, peak voltage is often stated. As always, read the datasheet. \$\endgroup\$
    – winny
    Feb 2, 2023 at 10:44
  • \$\begingroup\$ An ordinary older Lithium-Ion or Li-PO battery cell is stored and sold at 3.7V where it survives for a fairly long time. Its lifetime and number of charge-discharge cycles are reduced If it is stored lower than about 3V or is stored fully charged at 4.2V. It is ruined if it is discharged below about 2.8V and if it is charged above 4.2V. \$\endgroup\$
    – Audioguru
    Nov 26, 2023 at 2:19

1 Answer 1

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So your first question is what voltage are li-ion batteries. This depends on the type of li-ion cell you have, so you’ll need to read the datasheet. I have seen li-ions rated for anything in the range 2.5-3.2V as minimum voltage (fully discharged), and anything from 4-4.5V maximum voltage (fully charged). although 3.7V seems to always be quoted as nominal. So the quick answer is: 3.7V is nominal, full charged will be 4.x (where x depends on your particular battery).

Charging a battery gets more complicated. When I’ve designed a charger using a constant current, it’s a nice simple option of constant current source of 0.5A or so, with a maximum voltage of 4.5V, it would charge my 4.2V rated cells quickly, and when they’re full there’s only a 0.3V over voltage, which kept it within the safety margins for CE and UL (at the time a few years ago, the limits were changing last time I was looking into it). But you have a charging IC.

This charging IC of yours is giving you a proper CC-CV charging regime. You get to set the constant voltage value, which you’ll need to pick to align with you particular battery. You can also choose your charging current limit, again you’ll have to pick that depending on your particular battery.

But you’ve asked about what voltage you should put on the charging IC. That is defined in the datasheet as 3.75V to 6V, which give you the answer. I’d go for something around 5V, as the IC will power down and not charge the battery if VDD is less than the battery voltage plus 150mV (defined on page 5 of the datasheet). Clearly you can get away with you maximum battery voltage plus 150mV, but we don’t know what that is.

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