Post Go back to editing

Circuit for adding external ±500 mA range to AD5522

Category: Hardware
Product Number: AD5522

 

I designed and made a PCB board referring to the evaluation board of AD5522.
I confirmed the operation of the internal range and external ±80 mA range.
There is only one thing that does not work, which is connecting the external circuit for adding ±500 mA range and verifying its operation.
It does not work as intended.
I connected the circuit according to Figure 47 of the AD5522 data sheet, so that the OP AMP (current 1.0 A) operates as a follower.
The ±500 mA range resistor is connected to 2 Ohm.
And I set the PMU REGISTER bit name FORCE1/FORCE0 = 00, bit name C2/C1/C0 = 110.
But neither FV nor FI mode works, so please check the circuit connection and setting problems.
I attach the related circuit schematic  as below.

Top Replies

  • Hi.

    I responded to your first inquiry and I think there's nothing wrong with your schematic diagram. One thing I would like to ask is, have you tried writing C2/C1/C0 = 100 first to make sure you are in the external current range?

    Thanks,
    Mac

  • Hi,

    I tried writing C2/C1/C0 to 100.
    I applied voltage and current using the external current range connected to the OP AMP in the circuit diagram.
    It worked well only within ± 10V and -+ 50mA.
    I would like to know I can actually operate in FI mode or FV mode like the internal range with the external 500mA range?

    Thanks,

    TEST LINK

  • Hi,

    I write the results of the experiment divided into two cases.

    1) Writing C2/C1/C0 = 110 was set.
    The current range of 500mA was selected and FV mode was set.
    20 Ohms was connected to the channel output terminal and 1V was applied.
    The output terminal voltage was measured to 1V.
    2V was applied and the output terminal voltage was measured to 1V.
    The current is calculated to be 50mA.
    When the voltage is applied without resistance, the output terminal voltage is measured as the set voltage.
    2) Writing C2/C1/C0 = 110 was set and the current range of 500mA was selected.
    And FI mode was set.
    When applying either 500mA or 100mA without connecting resistance , the terminal voltage is measured to be about 0.25V.
    When the resistance is connected, the terminal voltage becomes 0V.
    Please check what the problem is.

    Thanks,

    TEST LINK

  • Hi Mac,

    I write the results of the experiment divided into two cases.

    1) Writing C2/C1/C0 = 110 was set.
    The current range of 500mA was selected and FV mode was set.
    20 Ohms was connected to the channel output terminal and 1V was applied.
    The output terminal voltage was measured to 1V.
    2V was applied and the output terminal voltage was measured to 1V.
    The current is calculated to be 50mA.
    When the voltage is applied without resistance, the output terminal voltage is measured as the set voltage.
    2) Writing C2/C1/C0 = 110 was set and the current range of 500mA was selected.
    And FI mode was set.
    When applying either 500mA or 100mA without connecting resistance , the terminal voltage is measured to be about 0.25V.
    When the resistance is connected, the terminal voltage becomes 0V.
    Please check what the problem is.

    Thanks,

    TEST LINK

  • Hi  ,

    I would like to know a few more details so we can help you better in investigating these problems you encountered. First one is that your schematic diagram does not show the connections inside the 5P-CON.

    For instance, are 'pin 3' and 'pin 4' internally shorted? Are 'pin 1' and 'pin 2' internally shorted too? As for the 20-ohm load, is it placed in between 'pin 1 / 2' and 'pin 3 / 4'? (see figure below to verify if the pin locations in red match with what are in your schematic diagram)

    Another thing I would like to know is the specific name of the op-amp you used as the high current amplifier.

    Regards,

    Gelo

  • Hi Gelo,

    Yes, I internally shorted 'Pin 1' and 'Pin 2' .

    Also, I shorted  internally 'Pin 3' and 'Pin 4' .

    I placed 20 ohm load in between 'pin 1 / 2' and 'pin 3 / 4'.

    and I  wrote 0x03FF4A0 in system control register.

    The op-amp I used is OPA548F/500.

    I wonder if the AD5522 can actually apply a current of 500mA. And can I use both FV and FI modes?

    Best Regards,

    TESTLINK

  • Hi @Testlink,

     

    Thank you for your confirmation on the pin locations and the op amp that you used.

     

    Regarding your question: “Can AD5522 actually apply a current of 500mA?”, the datasheet states that AD5522 can only output a maximum of ±80 mA by itself. To increase the current beyond ±80 mA range, an external high current amplifier is required.

    (Please refer to the text highlighted below. Note: This image was taken from page 31 of the AD5522 datasheet). 

     

    For now, I can only say that higher current range than ±80 mA is achievable through an external amplifier based on what's written in the datasheet but honestly, we currently have no sufficient data to support that.

    As for your second question: “Can I use both FV and FI modes?”, the answer depends on the current range that you are working with. According to the datasheet, FI mode can be used for the four internal current ranges which are ±5 uA, ±20 uA, ±200 uA, and ±2 mA as well as  for the ±80 mA current range (using an external sense resistor and internal amplifier) ; FV mode is the only option to use when operating at external current range greater than ± 80 mA by using an external sense resistor and external high current amplifier (Please examine the images below for more info. Note: These images were taken from the AD5522 datasheet).

     

     

    Please be assured that my team and I are investigating this and have had an internal discussion on whether AD5522 can support FI mode in higher current ranges and if 500 mA range is achievable via an external amplifier. We have decided to conduct some bench experiments to verify these questions. However, I have to inform you that our responses will be delayed due to a site shutdown that will take place next week. We will resume our work on Nov. 6 and continue to provide you with updates.

     

    Regards,

    Gelo

  • Hi Gelo,

    Thank you very much for your answer.

    I hope you and your team can find the solution to my inquiry.

    Have a nice weekend.

    Regards,

    TESTLINK

  • Hi  , 

    Apologies for the delayed response. I had problems with my setup and could not perform the experiment.

    I will get back to you with the results by friday.

    Thanks,

    Gelo

  • Hi Gelo ,

    I’m looking forward to good results.

    Thanks,

    TESTLINK