Can someone please help me? I'm looking for a solar panel charge to charge lithium 3.7V battery that works without a battery. I'm using one solar panel 6V, 12V or 24V which charges the battery and also supplies the power to the load. I need to be able to supply the power even though the battery is not connected or broken. How can I do this?
I found LT3652 part but I dont think this can do it. Or this part LTC4015 because it states the instant on when the battery is discharged.
Or could I design a switch that turns on when battery is not present and delivers power to the system? I was thinking to use a step down to 5V which is enabled only when there is no battery.
You mentioned a 3.7V lithium battery - is this the nominal voltage or the full charge voltage (basically, is this a LiFePO4 or Li-Ion/Polymer battery)? If nominal, what is the full charge voltage that you intend? Your answer here will determine what part I recommend for this application.
Also, you mentioned one solar panel but a range of voltages, can you elaborate on that? Will a variety of panels be used with this circuit or will the same panel always be used? And if the same panel, where do those voltages come from and why did you list three? Have you not decided on a panel yet?
Also, what charge current do you need?
The full charge voltage is 4.2V. Nominal is 3.7V. I'm using lipo 606066 3.7V 2400mah Lithium polymer battery.
Yes, it will be a one solar panel but it could be 6V, 12V or 24V but one at the time. I need one design that could work with either of these voltages.
I'm not sure yet what charge current. The battery capacity is 2400mah.
I decided to go for LTC4000-1 IC. Do you think its the right choice? It can take in a wide range of voltages and can supply power when the battery is dead.
LTC4162-L42M seems like a really good IC for my application.
I was asking if i would need a DC-DC converter before the IC like in LTC4000-1 part but it looks like I wouldn't need which is great. Has is got a buck converter built it?
I would use a DC-DC boost converter after the charging circuit because I need to supply 5V to the system.
What happens to the output when I use ,for example, a 12V solar panel? When the battery is connected it should provide 4.2V max if its fully charged. What about when the battery is dead or not connected? What sort of voltage I would expect at the output?
I'm looking to design a PCB very soon and I will test it myself. It would be great if you could provide the design files. I will check if I can simulate this IC using LTSpice as well.
Would you recommend a 4 layer board? Or I could get away just using a 2 layer board?
Is it possible for you to review my design once I finish it?
I've got another question. Will LTC4162 work with a polymer battery? Or should I use LiFePO4?
Thanks and Regards,
Does the battery need to have a protection? For example, LIPO 606066 that we are using at the moment.
Great, yes the buck charger is built-into the IC.
No matter what your solar panel voltage, the battery will be charged to the same 4.2V threshold.
The 'output' depends on how you connect your load to the charger. Normally, you would connect it to the VOUT node which is powered by VIN when present, or VBAT when VIN is not present. You can connect it directly to the battery, but there are a few drawbacks.
If connected directly to the battery and no battery is installed, it will not work. This is because the LTC4162 has a battery detection algorithm which would not allow charging (or powering the load in this case) if no battery is connected. If you connect the load to VOUT, you will not have this problem because it would be powered by VIN in that case.
So, instead of feeding your load directly from the battery and boosting to 5V, I might recommend that you use a buck-boost and power that from VOUT instead of the battery. Is that possible for you?
How many layers you need depends on the charge current level; what is it? I would recommend 4 layers if you can. You can probably get away with 2 but thermal operation will not be as good.
Yes, if you send the design I can take a look as well.
Yes, it will work with a LiPo battery. Refer to the -L datasheet for that. The LiFePO4 variants are detailed in the -F datasheet.
As for protection, it depends what you mean. One thing that the LTC4162 does not do is low-battery disconnection from the load, so that's a good thing to implement externally.
Yes, I will connect the load to VOUT as per typical application from the datasheet's first page. Does it mean that the output will be 4.2V still when the battery is not connected? Or will it be whatever is Vin?
Would you recommend using buck-boost converter because the output will be Vin when battery is not connected? So the output will be 4.2V with a battery and 12V is the battery is disconnected and the solar is panel is 12V. Which IC for buck-boost would you recommend? Maybe LTC3789 as per LTC4000-1 demo board? Or are there any simpler designs?
I meant the protection from under voltage for discharge or over voltage. At the moment we are using LIPO 606066 battery but we might move to LiFePO4 later which might wont have any protection.
I was thinking to add a voltage detection chip that would cut off the power from the system when the battery voltage is lower than 3.5V I think. Is that what you meant?
Maybe I could use LTC4000-1? Or do you think that LTC4162 still is the better solution?
We need 0.5A current but I will use a 4 layer board. It will be better for EMC.
The input will be VIN when present and the battery voltage when VIN is not present.
For a 5V output, I would recommend a buck-boost converter since your VIN is always greater than 5V and your battery is always less. As for which buck-boost, it depends on your requirements. For a lower load current, you could probably find a much simpler buck-boost than LTC3789.
Looks like LTC3130-1 could be a good choice, but I'm not sure how much load current you need.
LTC4162 will not over-voltage the battery, and you could set an alert to trigger on an over-voltage event if that did happen due to some other reason.
You could add an external chip to protect the battery during a low-battery event, OR take a look at the RUN feature of LTC3130-1 which will just disable the load if the voltage runs too low. You might have about 1uA drain on the battery total from the LTC4162 idle quiescent current and the LTC3130-1 shutdown quiescent current, but that might be a very acceptable amount for no added cost.
I think LTC4162 is a better solution, and with 0.5A charge current, you can use a 2-layer board.
I see. Please just confirm that the output voltage will be Vin when the battery is not present? That's why I would need a buck converter and if the battery is present I would need a boost converter.
What about using a buck converter to step down to 5V before the charging circuit and using a boost converter to step up to 5V after the charging circuit? It would be less efficient?
Thanks, I will have a look at the ICs you mentioned.
Typo in my last response corrected: the OUTPUT will be VIN when present and the battery voltage when VIN is not present.
Right a buck and then a boost would be less efficient and less cost-effective.
A buck-boost converter looks like a good option.
Is it more efficient to use a RUN option to shut-down the power if the battery voltage is too low or could I add a voltage detection circuit? LTC4162-L doesnt have that sort of feature integrated?
How do I provide my schematic and layout design for you to review? Maybe could you provide your email address? I haven't got a design yet but I might have in the next few weeks.