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Feather 328P CHG LED defect
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Feather 328P CHG LED defect

by Kamots on Thu Aug 22, 2019 6:01 pm

Order Number : 2109999-2317534159
Message : Hello! On this order, item number 3458 (328P Feather) may have a
defect which will need return or exchange. The "CHG" light for the battery
management chip strobes continuously when the board is powered via 5V (USB).

If I connect a battery then it operates normally. It seems like there is
some sort of fault with that part of the circuit which I have not experienced
on other similar boards (Particle Gen3).

Please let me know if this requires a return, or if there is an SMD part I
can check and potentially replace to fix the issue. Thanks!

Kamots
 
Posts: 2
Joined: Sun Nov 24, 2013 7:10 am

Re: Feather 328P CHG LED defect

by oesterle on Fri Aug 30, 2019 4:04 pm

Hi, Kamots!


It's normal for the charge light to flicker when USB is connected without a LiPo/LiIon battery. Other Feather boards use the same charge circuit, and show the same charge light behavior. It grabbed my attention, too, at first.

Ladyada discusses this in the Power Management section of the primary guide for your Adafruit Feather 328P - Atmega328P 3.3V @ 8 MHz.

Hope that helps!

What are you making?


Cheers,

Eric

oesterle
 
Posts: 648
Joined: Tue Sep 17, 2013 11:32 pm

Re: Feather 328P CHG LED defect

by Kamots on Fri Sep 06, 2019 6:53 am

Hi Eric!

Thanks for the reply! I checked and sure enough that article does have one sentence about it. However, this bothers me since I can't understand why it would do this by design. So, I did some research.

According to the schematic, the LiPo charge controller is an MCP73831T-2ACI/OT. The datasheet says that if no battery is present then the STAT pin (pin 1) should be High-Z. It seems this may be a design issue with the controller if it is strobing without a battery connected instead of being High-Z. Alternatively, maybe it isn't happy about something in the circuit design. I did notice that VBUS doesn't have a bypass cap as the datasheet suggests. I'm going to try a few things and see if I can find a solution to this. It may be a waste of time, but if I can't find a solution I'll likely remove the LED as it is fairly annoying especially when I am looking out for other LED indicators in my project but not staring right at it.

As for what I'm building, right now LoRaWAN stuff. There isn't a wide-coverage gateway in my area so I hope to set one up, but the 900MHz ISM band is fairly crowded with "smart" meters around here so it may be hopeless without some extensive filtering on the RF side. Also tinkering with other FeatherWing boards. I have a lot of them now.

Kamots
 
Posts: 2
Joined: Sun Nov 24, 2013 7:10 am

Re: Feather 328P CHG LED defect

by adafruit_support_mike on Fri Sep 06, 2019 10:37 pm

When no LiPo is connected, the voltage on the BAT pin is controlled by random leakage current within the circuit and across the surface of the PCB.

The MCP73831 sees those voltage changes as a LiPo behaving strangely, and hops between normal and error modes at random.

adafruit_support_mike
 
Posts: 58856
Joined: Thu Feb 11, 2010 2:51 pm

Please be positive and constructive with your questions and comments.