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ADS1246 Power Supply Issues

cody lohse
Intellectual 650 points
Other Parts Discussed in Thread: ADS1246, MSP430F2274

I am experiencing a strange problem. I am using the ADS1246, I have the unit on a custom PCB and the unit is mostly fully functional except for the issue that I am now having.

The problem is very strange to me, but I hope someone may have some intuition as to what is going on. The issue is related to the input power supply. If I run the ADS1246 from the regulated supply and the load(strain gage) from a output pin on the MCU, all works just fine. As soon as I try to run the ADS1246 and the load from the same source, the output from the ADS is severely attenuated or the ADS does not functional at all. If I change things around and run the ADS1246 from the MCU output pin and source the strain gage from regulated source I have the same issue.

I am using the MSP430F2274 at 3.3 V, the output pin on the MCU is at 3.242 V and VCC from the supply is at 3.324 V. I have lowered the voltage running to ADS1246 chip down to 2.7V and ran the load at 2.9V and everything still works fine (Thought it might be a voltage potential issue). I have confirmed that all of the ground connections in my system are common.

My original goal was to source the strain gage and ADS1246 from the output pin on the MSP430 and turn this on an off as I pleased.

Please help,

Cody

1106.protoV1.2.2_ant.pdf

  • 0
    TI__Guru** 113765 points

    Cody,

    My guess is you are running out of current for the startup of the ADS1246.  There will be an initial current demand for the startup that is higher than the general operating current.  You will need to make sure that you supply the necessary startup current.  Generally the strain gauge is lower impedance and draws a significant amount of current by itself (often in mA range.)  The amount of startup peak current for the ADS1246 will depend on the ramp rate of the supply voltage.  The larger the current draw from the MSP430, the lower the output high regulated output value will be seen.  You could supply the voltage from your main supply through a MOSFET turning it on and off via GPIO.

    Best regards,

    Bob B