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I designed a PCB, but I'm unsure whether this topology correct or best one. The circuit powered with Li-ion battery and the battery should charge over USB. When USB has not been connected, Step up-down IC supply 3.3Volt to the board. When USB has been connected, Li-ion charging and also supply power to the board. Both charging and working of board could be possible at the same time. Is there any drawback?

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  • \$\begingroup\$ U2 and U7 need part numbers. How much current is needed? Do you have question? \$\endgroup\$ Oct 28 '18 at 21:50
  • \$\begingroup\$ Ok.U2:LTC4056, U7:LTC3240 also D2 is not a diode,it's a led. LTC3240 can supply up to 150mA, that is sufficient. \$\endgroup\$ Oct 29 '18 at 8:50
  • \$\begingroup\$ My question is there any drawback drawing current from battery while it is charging? Second quesiton is this circuit manner(topology) suitable?just to sure \$\endgroup\$ Oct 29 '18 at 9:00
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UPDATE TWO

ltc4056 damaged 2 times, i'm try to understand the reason of this damage

this is my typo mistake. U2 ltc4054, not ltc4056.

Okay. This is a very simple circuit. I do not know how 2 of them burned up on you.


I only see one serious deficiency.
What will you do to keep the battery from being discharged so low the battery gets damaged?

You may want to consider adding an LTC1998 Voltage Reference for Battery Monitoring. You could use the BATTLO to shut down the LTC3240.

LOW BATTERY DETECTOR

Keep in mind the full featured MCP73871 costs about the same as the LTC4054. Low battery detect, battery temperature monitor, multiple power sources (USB and adapter), set max charge voltage and cutoff voltage, charge status indicator, and power good signal. All nice features you do not currently have. Just add resistors for settings and LEDs for status.


UPDATE ONE

ltc4056 damaged 2 times, i'm try to understand the reason of this damage

Notice in your schematic, pin 2 is connected to ground?

ISENSE (Pin 2): Sense Node for Charge Current. Current from VCC passes through the internal current sense resistor and out of the ISENSE pin to supply current to the emitter of the external PNP transistor. The collector of the PNP provides charge current to the battery.
Source: LTC4056 Datasheet

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Notice BAT pin 3 in your schematic?
BAT is pin 6.
BAT is an input, not output.

BAT (Pin 6): Battery Voltage Sense Input.
Source: LTC4056 Datasheet


Pin 3 is Base Drive Output, for the External PNP Pass Transistor. Provides a controlled sink current to drive the base of the PNP. This pin has current limiting protection
Source: LTC4056 Datasheet



I asked:

I do not see an inductor. Is your chip a charge pump and linear step down?

You replied:

As i said this is stup up/down converter. I think there's a inductor inside this. – Berker Işık

There are no semiconductor inductors.
There are different types of step-up and step-down typologies.
Your step-down is not a buck step-down. That is why I asked.

The LTC3240-3.3 is a charge pump step-up. That's okay.

The LDO step-down mode efficiency (87%) of this chip is okay at 100 mA.
You could do better with a buck step-down without a step-up mode. You should not need a step up mode. An Li-ion should not drop below 3.3V with a 100 mA load. You should make 3.4V as your cutoff.

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Li-ion are sensitive to being drained too low. You need to set an input voltage point where the regulator is shut down so the battery is not drained too low.

The reason I recommend the MPC73871 is you can use the LBO low battery output to shut down the 3.3v regulator. And the LBO voltage is programmable.

You could also instead use a buck step-down regulator with a programmable LBO/UVLO input.

END OF UPDATE



I would prefer a more sophisticated charger chip like the
MCP73871 Battery Charge Management Controller

You can use the LBO low battery output to shut down the 3.3v regulator.

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The 3.3V Regulator

Not much to say here without part number or max current.

I do not see an inductor.
Is your chip a charge pump and linear step down?

You do not need the buck/boost 3.3V regulator if your load is not too heavy. Use an LDO buck step down converter.
In the discharge curve of a 18650 Li-ion battery, the voltage does not reach 3.3V until near the end of the battery's capacity.

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Source: Panasonic 18650 datasheet

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  • \$\begingroup\$ Thanks,mcp73871 looks like complicated a bit. The board consumes less than 100mA. But battery selection haven't complicated yet. Just in case,i use step up/down converter. \$\endgroup\$ Oct 29 '18 at 8:56
  • \$\begingroup\$ Also, ltc4056 damaged 2 times, i'm try to understand the reason of this damage.Is there any topology problem looks like? When damaged, even if battery was not connected(U16 was void). LTC4056 provides about 4.2V to battery or U7 converter. Only ltc4056 damaged,not ltc3240. \$\endgroup\$ Oct 29 '18 at 9:05
  • \$\begingroup\$ typo error: complicated yet, correct one:completed yet. \$\endgroup\$ Oct 29 '18 at 9:09
  • \$\begingroup\$ I do not see an inductor. Is your chip a charge pump and linear step down? As i said this is stup up/down converter. I think there's a inductor inside this. \$\endgroup\$ Oct 29 '18 at 9:12
  • \$\begingroup\$ You have serious problems. See my UPDATE. \$\endgroup\$ Oct 29 '18 at 11:51
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A lithium-ion battery is considered to be fully charged when its charging current drops to a very low amount. With your load always connected to the battery then the charger never sees a low current so it might over-charge the battery.

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  • \$\begingroup\$ The LTC4054 automatically terminates the charge cycle when the charge current drops to 1/10th the programmed charge current after the final float voltage is reached. \$\endgroup\$ Oct 30 '18 at 4:45
  • \$\begingroup\$ That's OK. Also charge current can is adjustable with a resistor between PROG pin and GND. \$\endgroup\$ Oct 30 '18 at 8:37

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