AD5941 Output Current Range

Hi,

 Current through Darlington pair is controlled by below parameters in code:

pBATCfg->ACVoltPP = 300.0f; /* Pk-pk amplitude of excitation VBE */
pBATCfg->DCVolt = 1200.0f; /* Bias voltage of VBE*/

Transfer characteristic of this Darlington pair is shown in its datasheet:

Hi Akila，

1. I use Ltspice to simulation,change the V source does not change the output current significantly.But change the R3 from 62Ω to 2Ω， the vpp of output current will increase to about 400mA. Is there a problem with the simulation？

2. The AIN1 is just a monitor point？

3.pBATCfg->DCVolt = 1200.0f; /* Bias voltage of VBE*/

-> The max value is 2.4V?

4. pBATCfg->DCVolt = 1200.0f; /* Bias voltage of VBE*/

->The max value is 600mV?

Hi,

 1. Your simulation output behavior is correct and as expected.

2. Yes. AIN1 is just a monitor point.

3. Yes. max of DC is 2.4V

4. Max of AC is 607mV

Hi Akila,

Thank you for your reply, but  I still have some questions.

Simulation result as below figure1, DCVolt set 2.0V, ACVoltPP set 600mV, the VPP of output current just  about 18mA, can't reach to 50mA .

if I need output 350mA , Is there only a way to reduce the value of R3(62Ω)？

figure1, output current 18mA

figure 2,output current 330mA

Hi,

   Current through Darlington pair can be increased by increasing VBE and shown in graph. Maximum VBE is reached when R3 is 0 Ohms and DCVolt is set to max (2.4V).

Hi Akila，

Is there a formula for calculating input voltage and output current ?

The purpose of this circuit is convert Voltage to current ,  the same function can also be achieved using an OP-amp + mos ?

The formula about input voltage and output current is relatively simple.

Hi,

Yes. Purpose of this circuit is to convert ac voltage excitation to ac current excitation. Kindly refer to datasheet of Darlington pair for its transfer characteristics.

Hi，Akila

Thank you very much！

Hi，Akila

Refer to  CN0510 schematic， the ADC of ad5491 support  differential input ?

The volatage of battery or RCAL equal to (AIN3-AIN2)/441, how to set the input type of ADC?

Hi,

   AD5491's ADC supports differential input measurement.

   In BatImpedance example code in github, ADC input is set by

dsp_cfg.ADCBaseCfg.ADCMuxN = ADCMUXN_AIN2;
dsp_cfg.ADCBaseCfg.ADCMuxP = ADCMUXP_AIN3;