AD74413R Circuit implementation

Hi,

Kindly consider this as urgent and reply

  1. We are using image below for current sense 250ma by using Rsense 10R. External mosfet SW4 is used for sinking path (VIOUT_N pin not using/float). GND is connecting to SENSEL pin.    Is the current can be sensed by AD74413R? Is there any limitation?(note: We will ignore short circuit limit notification)
  2.  Also we are using below circuit for current sense 4-20mA. In that 24V is connecting to SENSEH pin. Whether current can be sensed by AD74413R by using below circuit?
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  • 0
    •  Analog Employees 
    on Apr 13, 2021 8:07 AM

    Hi, 

    1. I've checked the datasheet and it seems that the current input input range is specified to 0 to 25mA only with 100ohm resistor. Using a different value may impact the accuracy.  

    2. What's your Rsense value here? 

    I'll try to follow up the product owner to confirm and further assist you on this.  

    Thanks,

    Jellenie

  • 0
    •  Analog Employees 
    on Apr 13, 2021 2:44 PM in reply to JellenieR

    Hi Monisha,

    Please consider the circuit below. The current flow is from the 24V external supply. The switch is used to control the on/off of the current. The current flows from the 24V supply, through a resistor (say 10 Ohm), to I/OP through the load to ground. 

    In this case, the a 200mA current, will generate 2V drop across the 10 Ohm reistor. The AD74413R Voltage INput measurement can be used to measure the voltage between SENSEHF and SENSELF. No voltage drop should be generated in the second resistor as all the current flows in the 10Ohm. the voltage measured will be V = 200mA * 10 Ohm = 2V. 

    The combined resistance shown should add to 100 Ohm. This will will ensure that all all of the AD74413R functions still operate as specified. 

    To measure 4 - 20 mA from an externally powered sensor, you should just use the CUrrent Input, Externally powered mode of operation. The AD74413R will sink the current and the corresponding voltage will be measured between SENSEHF and SENSELF. 

    Thanks

    Bríde

  • Hi,

    1. Yes. But the Rsesnse one end(SENSE_H) needs to be connect to 24V. Because we are using 3 wire sink configuration(source w.r.t ad74413r). So we are plan to use external powered mode. is it possible?

    2.Maximum 200mA we can take. This is sinking requirement. i need 3 terminal. one for 24V, GND and other for current flow. so the third pin is common during sink and source.

  • 0
    •  Analog Employees 
    on Apr 20, 2021 8:30 PM in reply to Monisha

    Hi Monisha, 

    This is how we would propose to sink currents greater than 25mA (off-chip) and still measure the current with the Ad74413R. It is very similar to the sourcing proposal, only that the current flows through the load, onto the Ad74413R board and to ground. 

    In this case, all the existing functions of the AD74413R are still available for use. When sinking the 200mA, you can measure the voltage between SENSEHF and SENSELF. Voltage will only be dropped across the 10 Ohm resistor, so you will measure 2V for 200mA. 

    I hope this helps,

    Bríde

  • Hi Bride,

    In the above mode i need to use which mode,voltage input or Current INput? If voltage input means the datasheet shows voltage measure between SENSEL and AGND pin. Whether it is possible to measure100R resistor Voltage between SENSEL and SENSEH by using voltage input mode?

  • 0
    •  Analog Employees 
    on Aug 30, 2021 2:28 PM in reply to Monisha

    Hi Monisha,

    Apologies for the delayed response, I have been on vacation. 

    In the proposal above, try setting it in Voltage Input mode. Once the channel is configured write to the ADC_Config register (0x05) to change ADC_MUX to "01". This will ensure that you are measuring between SENSEHF and SENSELF. 

    You can also edit the ADC_RANGE as required. 

    Thanks,

    Bríde

Reply
  • 0
    •  Analog Employees 
    on Aug 30, 2021 2:28 PM in reply to Monisha

    Hi Monisha,

    Apologies for the delayed response, I have been on vacation. 

    In the proposal above, try setting it in Voltage Input mode. Once the channel is configured write to the ADC_Config register (0x05) to change ADC_MUX to "01". This will ensure that you are measuring between SENSEHF and SENSELF. 

    You can also edit the ADC_RANGE as required. 

    Thanks,

    Bríde

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