LiPo 3.3V Linear Regulation - Chip Suggestions?

What is your excitation voltage and what is your current draw? Do you have a schematic to share?

Regards,

Dave M.

By excitation voltage I believe you mean the battery right? in that case it would be the 3.4V to 4.2V of the LiPo battery.

I'm not entirely certain of my current draw, but I believe it to be around 360mA. The primary sources of this is the following:

XBee Wifi Module S6b, peak current of 310 mA

Teensy Proto Board, Peak Current 35 mA

Resistor Bridge, 10 mA

Amplifier, Negligible ~25 microA

Status LED's have some too, but I removed those from the design.

The circuit is designed to run from a nominal 3.3V for the whole system. I've included a schematic of the ADC portion that I believe is amplifying all variations from the power supply.

I was reading over the datasheet for the operation modes and noticed this compared to your schematic on the REF line. and Yes the Excitation was the bridge supply.

The issue I have had with this is that I have negative swing on my wheatstone bridge that would drive the voltage into the ground rail and even negative. To accommodate for that I put the ref voltage in the middle at 1.65V with the voltage divider. I then use this reading as a zero off the ADC and calibrate my bridge for whichever direction the sensor would see.

Could the noise be from the ref pin? As you can see I have heavily filtered the input the the amp but I have just a straight, unfiltered resistor divider for it.

"EDIT"

I just noticed the other image on your reply. This is more or less how I have the system setup with the exception being the ref pin as you mentioned. Actually the other exception is that I use the on board ADC of the microprocessor, not an independent one. I'm considering the advantages of having an independent ADC for improving my data rates and letting the processor do transmits over Wifi, but that might be a topic of another time.

From a trouble shooting point of view, can you run this from a bench power supply that you can select the voltage that you want.  With a bench power supply you can use it to remove that portion of the equation, and focus on the bridge and amp, then when you are sure its working they way you expect, switch back to the battery.  Also if you are bread boarding this, the bread board (The type and you can just plug into) adds capacitance to the circuit.  Break it in to small segments.  You can use a bench power supply to drive the Amp input and reference the grounds on the battery circuit and the bench supply and verify its operation.  Once you are sure each part works correctly, add on the next portion and retest.  Any RF powered items from the same power source you will want to insure RF is not being fed back through the power line.  If RF in not part of the circuit yet, be sure to look for it in the future when you add it.  You maybe surprised where the noise is coming from.

Regards,

Dave M.

dmaruska wrote:

From a trouble shooting point of view, can you run this from a bench power supply that you can select the voltage that you want. 

 

This is what first alerted me to the issue. I've been assembling the latest version of the prototypes that incorporated a PCB design instead of soldered perf board connections. The noise cleaned up significantly by going to a designated circuit as I expected, but as I assembled each system on the PCB I tested them independently. When I did this I was elated when I had next to no noise, of the order of roughly +/-1mV, however, when I connected the battery power circuit that noise jumped to +/- 5mV. (+/- 1mV even without shielded signal wire!) In the past I chased this problem by examining the power supply output on the scope and found it had ripple, but given the uncertainty with solder perf board I accepted this as the best accuracy I could easily obtain. With the PCB I got greedy and wanted a the cleaner signal that I was getting with the bench supply.

dmaruska wrote:

From a trouble shooting point of view, can you run this from a bench power supply that you can select the voltage that you want. 

 

This is what first alerted me to the issue. I've been assembling the latest version of the prototypes that incorporated a PCB design instead of soldered perf board connections. The noise cleaned up significantly by going to a designated circuit as I expected, but as I assembled each system on the PCB I tested them independently. When I did this I was elated when I had next to no noise, of the order of roughly +/-1mV, however, when I connected the battery power circuit that noise jumped to +/- 5mV. (+/- 1mV even without shielded signal wire!) In the past I chased this problem by examining the power supply output on the scope and found it had ripple, but given the uncertainty with solder perf board I accepted this as the best accuracy I could easily obtain. With the PCB I got greedy and wanted a the cleaner signal that I was getting with the bench supply.