AD5941 Potentiometry Basic Example and OCP Basic Example

Question

Hello, 
 I had the following question. 
 In the Application Examples of AD5940/41 Git you can find a Basic Application Example for Amperometry, Cyclic Amperometry, Voltammetry and Cyclic Voltammetry. 
 But I couldn't find an Application Example for Potentiometry or/and Open Circuit Potential. 
 Is there any of the application examples of AD5940/41 or ADUCM355 which could be taken as a basis for a Pententiometric Measurement Application or/and an Open Circuit Potential measurement ? 
 The only thread which goes into the direction of this topic is this one: 
 https://ez.analog.com/data_converters/precision_adcs/f/q-a/542089/ad5940-open-circuit-potentiometry 
 But I dont fully get it. 
 Can anyone provide a guidance which one of the application examples would the best one to start to implement a Potentiometric or/and Open Circuit measurement ? 
 Many Greetings

Akila · Accepted Answer

Hi, 
 These switch configurations (2) and (3) are done for generating excitation output and doing current measurement. 
 2) SW switch configuration for excitation output at CE0, sensing at SE0 and reference feedback at RE0, is as below: 
 If LPTIA is used for current measurement: 
 if(AppAMPCfg.ExtRtia == bTRUE) { lp_loop.LpAmpCfg.LpTiaRtia = LPTIARTIA_OPEN; lp_loop.LpAmpCfg.LpTiaSW = LPTIASW(9)|LPTIASW(2)|LPTIASW(4)|LPTIASW(5)|LPTIASW(12)|LPTIASW(13); }else { lp_loop.LpAmpCfg.LpTiaRtia = AppAMPCfg.LptiaRtiaSel; lp_loop.LpAmpCfg.LpTiaSW = LPTIASW(5)|LPTIASW(2)|LPTIASW(4)|LPTIASW(12)|LPTIASW(13); } 
 If HSTIA is used for current measurement: 
 if(AppSWVCfg.LPTIARtiaSel == LPTIARTIA_OPEN) /* User want to use external RTIA */ lploop_cfg.LpAmpCfg.LpTiaSW = LPTIASW(13)|LPTIASW(2)|LPTIASW(4)|LPTIASW(5)|LPTIASW(9)/*|LPTIASW(10)*/; /* SW5/9 is closed to support external RTIA resistor */ else lploop_cfg.LpAmpCfg.LpTiaSW = LPTIASW(13)|LPTIASW(2)|LPTIASW(4); 
 HsLoopCfg.SWMatCfg.Dswitch = SWD_OPEN; HsLoopCfg.SWMatCfg.Pswitch = SWP_OPEN; HsLoopCfg.SWMatCfg.Nswitch = SWN_OPEN; HsLoopCfg.SWMatCfg.Tswitch = SWT_TRTIA|SWT_SE0LOAD; 
 _________________________________________________________________________________________________________________________________________________ 
 3) LPDAC switch configuration : 
 if LPTIA is used for current measurement: 
 LpDacCfg.LpDacSW = LPDACSW_VBIAS2LPPA|LPDACSW_VBIAS2PIN|LPDACSW_VZERO2LPTIA|LPDACSW_VZERO2PIN; 
 
 If HSTIA is used for current measurement: 
 LpDacCfg.LpDacSW = LPDACSW_VBIAS2LPPA|LPDACSW_VBIAS2PIN|LPDACSW_VZERO2LPTIA|LPDACSW_VZERO2PIN|LPDACSW_VZERO2HSTIA; 
 _________________________________________________________________________________________________________________________________________________ 
 
 ADC configuration for current measurement:- 
 If LPTIA is used : 
 - without low pass filtering: 
 AD5940_ADCMuxCfgS(ADCMUXP_LPTIA0_P, ADCMUXN_LPTIA0_N); 
 - with low pass filtering: 
 AD5940_ADCMuxCfgS(ADCMUXP_AIN4, ADCMUXN_LPTIA0_N); 
 
 If HSTIA is used: 
 AD5940_ADCMuxCfgS(ADCMUXP_HSTIA_P, ADCMUXP_HSTIA_N); 
 
 ADC configuration for OCP measurement:- 
 AD5940_ADCMuxCfgS (ADCMUXP_VSE0 ,ADCMUXN_VZERO0); // for measurement of SE0 w.r.t. VZERO0 
 AD5940_ADCMuxCfgS (ADCMUXP_VRE0 ,ADCMUXN_VZERO0); // for measurement of SE0 w.r.t. VZERO0)

Akila · Answer

Hi, 
 1) ADCMUXN_LPTIA0_N refers to -ve input terminal of LPTIA. 
 As shown in above diagram, if LPTIA0 +VE input is connected to Vzero, 
 then, 
 voltage at ADCMUXN_LPTIA0_N = voltage at ADCMUXN_VZERO0. 
 Hence both can be used interchangeably here. 
 
 2) Yes. Opening SW2 removes excitation output.

Akila · Answer

Hi, 
 LpAmpCfg.LpTiaSW = LPTIASW(8) | LPTIASW(4); 
 means, 
 - SW6 connects -ve input of PA to +ve input of LPTIA 
 - SW7 connects -ve input of LPTIA to SE0 via RLoad 
 - All other switches are left open. 
 
 Hence by this configuration, 
 - CE0 is shorted to RE0. 
 - By the transfer function of a -ve feedback amplifier: 
 
 Rf = RTIA 
 Rg = Rload 
 Vin = VCE0 
 SE0 is assumed shorted to GND. 
 Hence open circuit potential across CE0 and SE0 = VCE0 = Vin = Vout * (-Rload/Rtia)

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AD5941 Potentiometry Basic Example and OCP Basic Example

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