AD5422 Protection Diode

Dear team:
Consult Figure 82 in the AD5422 data sheet. How the Schottky diodes D2 and D1 are selected (can you give a recommendation)? Operating voltage is 24V. Here's what D2 and D1 do.

  • 0
    •  Analog Employees 
    on Apr 5, 2018 6:07 AM

    Hi lijie,

    This is briefly discussed on the TRANSIENT VOLTAGE PROTECTION section on page 39 of the data sheet. The  diodes that you should select should have enough power rating to handle the transients you want it to be protected from.

    Best regards,

    Rainier

  • Dear Rainier,

    Due to my lack of experience, a brief discussion of the transient voltage protection section on page 39 of the data sheet does not help me to correctly select Schottky diodes. Such as the Schottky diode protection voltage is 24V? Whether the reverse current and forward voltage need to be low, how little influence the 4-20mA output and so on. Please give instructions.

    Best regards,

  • 0
    •  Analog Employees 
    on Apr 6, 2018 5:33 AM

    Hi lijie,

    Looking at figure 78 on the data sheet, the power diodes and Rp help protect the IOUT pin from overvoltages.

    The power diodes that you should choose should have a low forward voltage so that it would have a faster turn-on time.

    Rp will limit the current flowing through the power diode, hence preventing it from getting damaged due to high dissipation.

    Lets say you have a 0.3V forward voltage for the selected power diode and AVDD=15V. You can compute for the resistor by this equation:

    Rp= (VOUT-0.3V-AVDD)/Id

    Consider Id based on the maximum power dissipation you want on the power diode.

    Don't use an Rp that is very large as this would affect the compliance voltage (AVDD-2.5V) of the IOUT during normal operation.

    Refer to INDUSTRIAL ANALOG OUTPUT MODULE section (page 41)  and figure 83 for the recommended TVS diodes.

    Best regards,

    Rainier

  • I see a similar circuit. The power diode uses Schottky diodes, model RB751S40. Ask, this model is suitable for 24V power supply circuit.

  • 0
    •  Analog Employees 
    on Apr 10, 2018 6:58 AM

    Hi lijie,

    Kindly refer to CN-0321 . it used BAS70-04LT1 as power diodes which is suitable for 24V supply.

    Best regards,

    Rainier