CC MLambe Brandon NeoXu
Hope all is well. I am testing EVAL-AD5940ELCZ to perform CV and started from example AD5940_Ramp.
I have two questions please:
1. The instructions say:
"Actual start voltage on the sensor pin is VzeroPeak + RampPeakVolt
Was it meant:
"Actual start voltage on the sensor pin is VzeroStart + RampStartVolt" ?
2. Using dummy network B, I ran the example and got the following CV curve. However it wasn't what i expected given linear nature of dummy network B.
I attach the measurement file in Excel form for convenience.
Thank you very much,
Yes, the actual voltage on the pin is VzeroStart + RampStartVolt.
I suspect you may be using a TIA gain resistor that is too big and the voltage at the output of the LPTIA is beyond the input range of the ADC. Refer to AN-1563 pg. 9 for details on calculating an optimum value.
Thank you very much! Yes, setting correct value of TIA gain resistor resolved the issue.
Also, I wonder what would be the best way to enable CV measurements in a loop/continuous mode or a predefined number of ramps?
In the AD5940Main.c file once one loop finishes you can call function AppRAMPCtrl(APPCTRL_START, 0); This will start the measurement again. You will need to include some simple logic to check that the measurement has fully finished before calling this. For example once StepNumber results are read restart.
Thank you. That approach worked with one fix of the example code: in the section of ISR AppRAMPISR that services End of Sequence Interrupt, call to AppRAMPCtrl(APPCTRL_STOPNOW, 0) stopping the wakeup timer had to be commented since otherwise AppRAMPCtrl(APPCTRL_START, 0); will not restart the next measurement. And since CV are multi-cycle in nature that seems fine.
I also had to call AppRAMPInit(AppBuff, APPBUFF_SIZE); prior to restarting each next measurement.