I have two main concerns right now:


1) Load detection circuit to keep pack power outputs disconnected until the battery is plugged into the device:
I have limited pins out of my battery pack. I need to design a circuit that can determine that the battery pack has been plugged into the device and only then will it turn on it's output.

Main request: I really need to make this work with the power output pins themselves. The only other pins I have available are I2C pins going to the device.

So on the BMS I am using the BQ29700 to protect the cell. I was wondering if I could trick an OVP or UVP on that chip depending on a resistor divider that is on the device so when the battery plugs in, the resistor divider on the device comes into circuit and helps satisfy OVP or UVP and then the BQ29700 turns on the pack output.

But ideally this is done through one of the pack output pins (+ or -).

2) I2C of the coulomb counter gas gauge BQ27Z558YPHR:
The gas gauge will always be on, always connected to the cell. But some of my pack output pins will be i2c.

When I connect the battery to the device, the battery will power on the device and the microprocessor on the device will come alive and then start to ping the gas gauge via i2c. How do i keep the bus from being glitched and not able to reset the gas gauge?

Can I keep the pull up resistors on the device so the gas gauge i2c bus isn't pulled high until it's connected? Can I use a i2c mux/switch and maybe that can reset the bus? Maybe I Can reset that via i2c?

Also, I will probably be using an i2c differential driver on the device to the battery. Maybe that can help keep the bus from getting glitched?


Thanks !

 

Cannot comment on anything:

No schematic, no block diagram, no context.

 

I’m asking for help to design the concept of the circuit. I can’t have a schematic or block diagram without the concept.
I felt like I gave plenty of context.

Do you have any questions for me to clear something up?

 

 

 

 

Cannot comment on anything:

No schematic, no block diagram, no context.

Ok posted the block diagram, schematic references from the two chips mentioned, and my post honestly full of context and info. If I wasn't clear about something please ask and I can address something I may have missed.

Since I'm asking for help with starting a design, I can't show schematics I don't have. I don't know how to even start the load detection circuit.

I do not need help with the reference designs. As stated in my first post, I need a creative idea on how to detect a load and turn on the pack output's. perhaps a clever way to use the protector cell. or maybe adding another transistor with some load detection.

 

Why do you need to "detect" the load?

 

How do you detect a load without power?
Do you have a backup power ?

 

Welcome to AAC.

How is the load connected? The obvious thing is to choose a connector that can detect the insertion or use extra pins to make your own detection in the form of a jumper.

 

Why do you need to "detect" the load?

I want the batteries power output terminals to be off or isolated until it is connected to the device.

Welcome to AAC.

How is the load connected? The obvious thing is to choose a connector that can detect the insertion or use extra pins to make your own detection in the form of a jumper.

I am currently limited to the number of pins (pogo spring style contacts) by the mechanical engineer.

How do you detect a load without power?
Do you have a backup power ?

I do not have backup power. I would love an 'aux' power pin to supply a little bit of power to facilitate this negotiation.

My thought was a resistor divider. Top end is on the battery pack iteself and connected to the battery. So the output of the divider would be battery voltage. But then when connected, the other half of the divider is on the device and so now the output voltage changes. But that doesn't seem possible when the pin would be the main power pin.

I can come up with plenty of ways to do this. but the clever solution of just using the + and - pins has eluded me. Perhaps not possible. but I wanted to pose this to the community.

 

I am currently limited to the number of pins (pogo spring style contacts) by the mechanical engineer

It seems that you need to negotiate at least one more, or maybe you could use a high value resistor across two of them that won‘t interfere but can be used to sense the connection.