Hello, a few colleagues and I are working on a project that includes a battery charging circuit using an MCP73831T charging IC. Everything is fine until I connect the battery to the circuit, in which it just begins to smoke. What I do not understand is that the circuit is wired the same way that it is in the datasheet. I will post the circuit diagram and datasheet below. I cannot for the life of me figure out why it would do this. Do any of you have any ideas?

 

Something is definitely wrong. My best guess is that you have exceeded the "Absolute Maximum Ratings" on one or more pins. Alternatively you have reversed power and ground connections. Your diagram is poor, unreadable and in the wrong orientation, so I can't tell much from it.

 

I have used that chip to charge rechargeable lithium batteries. Never a problem. As for smoking the chip, the usual cause is pilot error.

Show your actual circuit and a picture of how it is connected.

 

Something is definitely wrong. My best guess is that you have exceeded the "Absolute Maximum Ratings" on one or more pins. Alternatively you have reversed power and ground connections. Your diagram is poor, unreadable and in the wrong orientation, so I can't tell much from it.

I will make sure tomorrow that my battery polarity is indeed correct tomorrow. Everything is at school, so I have to wait until tomorrow. As for the circuit diagram I posted...I know it is in the wrong orientation, but the picture quality is WAY readable. What makes my diagram "poor"?

 

I will make sure tomorrow that my battery polarity is indeed correct tomorrow. Everything is at school, so I have to wait until tomorrow. As for the circuit diagram I posted...I know it is in the wrong orientation, but the picture quality is WAY readable. What makes my diagram "poor"?

There is low contrast on what I think is the chip we are talking and the lettering in the image is too small.

 

As for the circuit diagram I posted...I know it is in the wrong orientation, but the picture quality is WAY readable. What makes my diagram "poor"?

Apparently, “way readable” is in the eye of the beholder. How old are you anyway? My eyes can’t read it even while wearing readers! And try reading a schematic oriented the wrong way on a monitor which you can’t rotate. Basically, I give up in these cases when the TS isn’t polite enough to make it easy for people giving of their time freely. Disrespectful.

 

Apparently, “way readable” is in the eye of the beholder. How old are you anyway? My eyes can’t read it even while wearing readers! And try reading a schematic oriented the wrong way on a monitor which you can’t rotate. Basically, I give up in these cases when the TS isn’t polite enough to make it easy for people giving of their time freely. Disrespectful.

Ok. It's readable just wrong orientation. Don't think that's grounds for calling me "disrespectful". I think you are pushing it a little bit. I will fix the issue...

 

Ok. It's readable just wrong orientation. Don't think that's grounds for calling me "disrespectful". I think you are pushing it a little bit. I will fix the issue...

Other than orientation the image looks fine. Here's a rotated copy:

 

 

Other than orientation the image looks fine. Here's a rotated copy:
View attachment 196399

thanks for verifying that and rotating it. I didn't think it was that bad

 

thanks for verifying that and rotating it. I didn't think it was that bad

Two possible explanations for the hot IC are: (1) the battery polarity is reversed, (2) all is working well but you have provided no heat sink for the IC while using it at its highest current rating. The intent (from the datasheet) is that the tiny SOT23-5 IC would be soldered to a 4-layer PCB with each layer having as much copper as possible in the general area of the IC. If you have not taken steps to remove heat from the IC, it may run very warm/hot and indeed may smoke (not good). I have no experience in heat sinking SOT23's, but perhaps someone else can suggest a way to provide adequate heat sink. Another possible approach would be to use a resistor higher than 2K to set a lower current and reduce the power dissipation in the chip; that might be worthwhile for troubleshooting.

 

Two possible explanations for the hot IC are: (1) the battery polarity is reversed, (2) all is working well but you have provided no heat sink for the IC while using it at its highest current rating. The intent (from the datasheet) is that the tiny SOT23-5 IC would be soldered to a 4-layer PCB with each layer having as much copper as possible in the general area of the IC. If you have not taken steps to remove heat from the IC, it may run very warm/hot and indeed may smoke (not good). I have no experience in heat sinking SOT23's, but perhaps someone else can suggest a way to provide adequate heat sink. Another possible approach would be to use a resistor higher than 2K to set a lower current and reduce the power dissipation in the chip; that might be worthwhile for troubleshooting.

Ok so I did verify that it was indeed reverse polarity. The batteries that we ordered from amazon were different from those from Adafruit. The red wire on the ones from amazon was actually the ground wire and vice versa, which is weird...but I guess its my fault as I didn't check polarity first. Thank you everyone for your responses

 

Amazon sells cheap clothing and shoes. They and the joints they buy electronic things from do not know about battery polarity.