Could someone please explain me what is the 0.4Ω resistor at the Vcc pin (yellow color)? Why it is surrounded by a dashed rectangle? Should I add such kind of resistor when I design my circuit?
TP4056 and Resistor at VCC – Usage Guide
batteriescharger
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I like the answer you suggested a lot. I think it is a good idea. I would suggest just a slight variation as follows:
Also, please work through the corner cases and unusual circumstances such as when the battery is dead, and arduino cannot power on. Will the charger be stuck in a zero charge current mode? Maybe a strategic pullup or pulldown somewhere, or a large resistor in parallel with RPROG and 100uF cap to insure small charge current even when PWM is off.
Great job!
McKenzie
keyword: power path controller, ideal diode
something like that http://www.linear.com/product/LTC4417
look also at others vendors, like TI, Fairchild, On semi
Implementation is possible with discrete components only, cheaper but less efficient.
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Best Answer
If you leave out the resistor and charge a battery with 1A (maximum current that the TP4056 can do) then the TP4056 will have to dissipate: 5.0 V - 4.0 V = 1.0 V * 1 A = 1 Watt (I'm assuming about 50% battery charge so 4.0 V). That's a lot for such a small SOP package and the TP4056 will get quite hot.
If it gets too hot it will lower the current but then your battery will charge slower.
This is where the 0.4 ohm resistor comes in, it will drop 1 A * 0.4 ohms = 0.4 V. That means the TP4056 will now only need to drop 0.6 V. At 1 A that means 0.4 W is dissipated by the resistor and " only" 0.6 W needs to be dissipated by the TP4056. This might be just low enough for it not to become too hot.
So if you are going to charge your battery with about 0.5 A to 1 A, then I would add the resistor.
If you're going to charge your battery with less than 0.5 A you can probably safely leave out the resistor.
Oh the dashed rectangle: it means that this resistor will get slightly hot and to cool it it is advised to keep other components out of the way and using somewhat larger copper areas on the PCB connecting to the resistor is advised as that helps to keep it cool.