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ADUCM355 CV and SWV behave differently when external Rtia is selected

Hello,

I have been testing both the Cyclic Voltammetry and Square Wave Voltammetry codes lately. I have noticed that for both codes, the desired ramps are generated and can be seen in the oscilloscope (voltage between shorted CE-RE and WE).

However, when I modify the code to:

pRampCfg->LPTIARtiaSel = LPTIARTIA_OPEN; 

to use an external resistor, the CV code is producing the desired ramps, but in the case of SWV it is either generating a constant -1 V voltage, a constant 0 V voltage or the desired ramp (between -0.5 V and 0.5 V). The initial voltage just after pushing the reset button on the board is around -1.25 V in all cases and lasts around 1 second before the oscilloscope displays one of the aforementioned voltages. Please see the figures below.

-1 V constant value

0 V constant value

Desired ramp

Do you know why it is behaving like this?

Thank you,

Jimar.