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Possible to create custom Vbias for AD5941?

Product Number: AD5941

Hi,

I wanted to ask if it was possible to use a DAC from an MCU rather than using the LPDAC for creating a bias for EIS measurements? This is in an attempt to use a lower Vzero value than what is currently applicable. If so, how would I go about doing this while superimposing onto the HSDAC from the AD5941? 

Additionally, in the impedance code: 

 LPDACCfg_Type lpdac_cfg;
   
    lpdac_cfg.LpdacSel = LPDAC0;
    lpdac_cfg.LpDacVbiasMux = LPDACVBIAS_12BIT; /* Use Vbias to tuning BiasVolt. */
    lpdac_cfg.LpDacVzeroMux = LPDACVZERO_6BIT;  /* Vbias-Vzero = BiasVolt */
    lpdac_cfg.DacData6Bit = 0x40>>1;            /* Set Vzero to middle scale. */
    if(AppIMPCfg.BiasVolt<-1100.0f) AppIMPCfg.BiasVolt = -1100.0f + DAC12BITVOLT_1LSB;
    if(AppIMPCfg.BiasVolt> 1100.0f) AppIMPCfg.BiasVolt = 1100.0f - DAC12BITVOLT_1LSB;
    lpdac_cfg.DacData12Bit = (uint32_t)((AppIMPCfg.BiasVolt + 1100.0f)/DAC12BITVOLT_1LSB);
    lpdac_cfg.DataRst = bFALSE;      /* Do not reset data register */
    lpdac_cfg.LpDacSW = LPDACSW_VBIAS2LPPA|LPDACSW_VBIAS2PIN|LPDACSW_VZERO2LPTIA|LPDACSW_VZERO2PIN|LPDACSW_VZERO2HSTIA;
    lpdac_cfg.LpDacRef = LPDACREF_2P5;
    lpdac_cfg.LpDacSrc = LPDACSRC_MMR;      /* Use MMR data, we use LPDAC to generate bias voltage for LPTIA - the Vzero */
    lpdac_cfg.PowerEn = bTRUE;              /* Power up LPDAC */
    AD5940_LPDACCfgS(&lpdac_cfg);
What does the DacData6Bit equal to? I know it's set to a Hex value of 32, but what is that the equivalent of Vzero in terms of voltage? 
Thank you!
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  • Hi,

    DacData6Bit =32 corresponds to 1100mV.

    As shown in the figure below (highlighted part), the output of external DAC (Bias and zero outputs) can be wired OR to P and N inputs of excitation amplifier.

    That is, if

    DswitchSel = SWD_CE0;
    PswitchSel = SWP_RE0;
    NswitchSel = SWN_SE0;
    TswitchSel = SWT_SE0LOAD;

    then, Vbias and and Vzero from external DAC can be wired OR to RE0 and SE0 pins respectively.

Reply
  • Hi,

    DacData6Bit =32 corresponds to 1100mV.

    As shown in the figure below (highlighted part), the output of external DAC (Bias and zero outputs) can be wired OR to P and N inputs of excitation amplifier.

    That is, if

    DswitchSel = SWD_CE0;
    PswitchSel = SWP_RE0;
    NswitchSel = SWN_SE0;
    TswitchSel = SWT_SE0LOAD;

    then, Vbias and and Vzero from external DAC can be wired OR to RE0 and SE0 pins respectively.

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