BQ35100: Schematic review and explanation of sense resistor to ground connection

Hello Mike,

This trend has been assigned and will be answered promptly

Thank you,
Alan 

Thanks for the feedback.  Ok, so the (-) terminal of the battery is only connected to Rsense and no where else on the board, correct? I plan on using a standard AA lithium battery (https://www.digikey.com/en/products/detail/micropower-battery-company/XL-060F%2520(AA)/17147238?gclsrc=aw.ds&&utm_adgroup=&utm_source=google&utm_medium=cpc&utm_campaign=PMax%20Shopping_Product_Low%20ROAS%20Categories&utm_term=&utm_content=&utm_id=go_cmp-20243063506_adg-_ad-__dev-c_ext-_prd-17147238_sig-Cj0KCQjwhMq-BhCFARIsAGvo0KeajK5SvWxUZQMywoQGo01z3pcgGY5ohHK5gjz_Up1P-iiRdCj9sYgaAumJEALw_wcB&gad_source=1&gclid=Cj0KCQjwhMq-BhCFARIsAGvo0KeajK5SvWxUZQMywoQGo01z3pcgGY5ohHK5gjz_Up1P-iiRdCj9sYgaAumJEALw_wcB&gclsrc=aw.ds).  How would it be wired when there are only two terminals on the battery?

A couple additional questions that came up after reviewing the datasheet further.  

1.) My processor operates at 1.8V.  I believe REGIN (Pin 6) needs min of 2.7V.  Should Pin 6 be at VBAT (3.6V) rather than 1.8V?

2.) With the processor operating at 1.8V and the BQ35100 utilizing VABT (3.6V), will I need to use a level shifter for the I2C communication?

Hello Mike,

This AA lithium battery should work for your system but for your Rsense to sense the current going through your system it needs to carry the load. The way that a Rsense work is by ohm's law V=IR where the resistnace is a know factor and the ADC is able to read the voltage so that means that current can be read. The Rsense needs to be in series from the battery negative to your load negative, meaning that it would essentially act as a path for the two points.

1.)REGIN acts as the LDO meaning that it acts as a voltage source for mainly for level shifting. This means you wouldn't input voltage to this pin

2.) Level shifter is a common tool for I2C communication to bring the voltage to the necessary voltage ranges. I would recommend using REGIN to bring up the  voltage to 1.8V

Thanks for the response.  Ok, that makes sense.  I will update the schematic to reflect this.

How can REGIN be used to raise the voltage to 1.8V? According to the datasheet, this pin requires an input voltage between 2.7V and 4.5V (see page 21 below), however, it appears from maximum ratings this would be an acceptable voltage. Can you confirm if 1.8V is an acceptable voltage into the REGIN pin.  Would that produce 1.8V on the REG25 pin?  Could you clarify how this should be configured to interface with a 1.8V system.  

Hi Alan,

Following up on this question, have you had a chance to review?

Thanks

Mike

Hello Mike,

Sorry I miss spoken and yes the input voltage should be between 2.7V and 4.5V and does not produce 1.8V on the REG25 pin. I would follow the screen shot you highlighted.

Hello Mike,

I followed it up on the message above.

Thank you,
Alan