USB/DC/Solar Lipo Charger AND Buck Boost Converter

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rifo
 
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USB/DC/Solar Lipo Charger AND Buck Boost Converter

Post by rifo »

Hello,

I am planning to use the USB/DC/Solar Lipo charger in a project of mine to power 3.3V system. I have read the tutorial at adafruit and saw the warning about load sharig feature of MCP73871. The load output voltage can be as high as 6VDC.

So in order to harness the most out of my lithium battery, do you think I can use a buck boost converter (like tps63060 from ti)? If I simply use a LDO then I guess I'll probably have problems when the lithium battery voltage gets less than 3.4V

I would be happy to hear your suggestions about the best way to do this.

Thanks a lot :)
rifat

buck boost converter tps63060

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adafruit_support_bill
 
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Re: USB/DC/Solar Lipo Charger AND Buck Boost Converter

Post by adafruit_support_bill »

A buck/boost should work fine in that application. Just be sure that it is rated to handle the current requirements of your load.

rifo
 
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Re: USB/DC/Solar Lipo Charger AND Buck Boost Converter

Post by rifo »

Hello Bill,

Thanks a lot for the answer. I'll just draw the schematic for the buck boost converter in eagle but I have 2 more questions

1) This may be a stupid question but I couldn't find the answer in the datasheet. If no power is supplied (neither the solar panel nor the DC input is plugged, I just want to have the system running off the battery) to MCP73871 then do I still see Vbat on the OUT pin? or is the case that no power is supplied to the system (which IMHO wouldn't make sense:D )

2) In order to preserve battery life, I want to shutdown the buck boost converter when I see the Low Battery Output case on Status Pins of MCP73871, hence
STAT1 should be LOW
STAT2 should be Hi-Z
PG should be Hi-Z

If no power is supplied to MCP73871 then Hi-Z case doesn't make sense hence I can't determine when to shutdown the system and the battery can be depleted. Can you please clarify whether I am missing something?

Thanks a lot for your help

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adafruit_support_bill
 
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Re: USB/DC/Solar Lipo Charger AND Buck Boost Converter

Post by adafruit_support_bill »

1 - yes, you will have battery power at the load terminals when there is no input power.

2 - there isn't a real low-battery indicator on that charger. The batteries we sell have a low-voltage cutoff built into the protection circuit. Other than relying on that, you wold need to build some circuit to monitor the battery voltage yourself.

rifo
 
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Re: USB/DC/Solar Lipo Charger AND Buck Boost Converter

Post by rifo »

Great! I can start drawing the schematic now:)

By the way, I have checked the Lipo datasheet, it says that the cut off voltage is 3.0 V (pack datasheet says that it's 2.7V though).
I guess I'll want the cut off voltage to be 3.2V so that battery lifetime is extended. I have found an supervisor IC BD45322G-TR
I think it should work if I feed Vbat (and NOT the output of MCP73871) into the supervisor IC and connect its output to EN of the buck boost converter

I hope I am not messing something up by doing this :D

thanks a lot one more time

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Re: USB/DC/Solar Lipo Charger AND Buck Boost Converter

Post by adafruit_support_bill »

I think it should work if I feed Vbat (and NOT the output of MCP73871) into the supervisor IC and connect its output to EN of the buck boost converter
That sounds like it should work.

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