This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AMC7834: IOVDD Amplitude

Part Number: AMC7834

Tool/software:

Hi team,

When Address (0x17) CLAMP Configuration bit1 (DAC34-CLAMP) is set to 0, IOVDD amplitude changed significantly.
In the customer's system, only DAC4 is floating.
Could you suggest any possible reasons to change the IOVDD amplitude?

Best regards,
Kazuki Itoh

  • Hi Itoh-san,

    A change in the IOVDD is odd. Could you give me a list of all of the voltages in the system (IOVDD, AVDD, DVDD, AVCC, and AVSS) before and after setting the clamp voltage? What value is DAC3 at? DAC4 floating shouldn't cause any issue.

    Thanks,
    Erin

  • Hi Erin,

    Sorry for the delay.
    Please find the results below.
    It looks like DAC setting Adress 0x30 - 0x32 is effecting the results in addition to clamp setting.

    Befor setting clamp voltage | #1

    • IOVDD:3.269V(typ) / 3.289 V(max) / 3.243 V(min)
    • AVDD:5.0 V(typ) /5.023 V(max) / 4.982 V(min)
    • DVDD:4.99 V(typ)/5.022 V(max) / 4.984 V(min)
    • AVCC:4.99 V(typ)/ 5.042 V(max) / 4.969 V(min)
    • AVSS:-5.025 V(typ)/ -5.055 V(max)/ -4.984 V(min)

    After setting clamp voltage | #2

    • IOVDD:3.277 V(typ) / 3.498 V(max) / 3.099 V(min) | Amplitude getting larger
    • AVDD:5.001 V(typ) / 5.018 V(max) / 4.982 V(min)
    • DVDD:5.001 V(typ) / 5.018 V(max) / 4.982 V(min)
    • AVCC:5.001 V(typ) / 5.021 V(max) / 4.961 V(min)
    • AVSS:-5.025 V(typ) / -5.054 V(max) / -5.01 V(min)

    Behavior Customer Observed

    Except for #4, IOVDD amplutude get larger (The voltage on #2 above)

    1. Start-up (#2)
    2. After setting below (Register settings except for default are listed) (#2)
    Item Address Parameter Data
    1 0x02 Power Mode 0002
    2 0x10 AMC Configuration 0 1300
    3 0x12 ADC MUX 4F00
    4 0x16 DAC Range 0005
    5 0x17 CLAMP Configuration 0000
    6 0x1C DAC/ADC Trigger 0001
    1. DAC1-3 set to 0x333(-4V) (#1)

    2. When 2 and 3, set bit0 (DAC12-CLAMP) or bit1(DAC34-CLAMP) to 0->1 on Adress(0x17) CLAMP Configuration

    3. When 2 and 3, set any of DAC1-3 to 0x000(-5V) (#2)

    Please let me know any setting of the possible cause.
    Is there any effect from VCLAMP 1/2 pin?
    Right now, there's pull up voltage applied.

    Best regards,
    Kazuki Itoh

  • Hi Kazuki,

    Thank you for the information. I'll be able to use this to test on my own setup. What pullup are you using? Is it a pullup on the CLAMP pin? To which voltage? If your customer is able to send a schematic that would be helpful as well.

    Thanks,
    Erin

  • Hi Erin,

    The IOVDD amplitude variation is likely due to the customer's power supply in the test setup.
    Sorry for the confusion.

    With respect to the clamp voltage, it corresponds to VCLAMP(1/2) on 29 or 30 pin.
    2.5V is coming from DVDD(+5.0VA) divider.
    When using bit 0 (dAC12-CLAMP) of CLAMP Configuration on Address (0x17) or bit1 (DAC34-CLAMP) as 0, should it be pull-down?

    Best regards,

    Kazuki Itoh

  • Hi Itoh-san, 

    Erin is reviewing and will provide some suggestions soon. 

    Best,

    Katlynne 

  • Hi Itoh-san,

    2.5V is good for the CLAMP. It should end up being -7.5V CLAMP. This voltage is dependent on your VSS voltage though, so if your VSS is not at least -7.5V, your CLAMP will not be able to reach that voltage. If DAC12-CLAMP bit is 0, that means DAC1 and DAC2 are operating normally, not pulled down. If the bit is 1, the output should be set to the CLAMP voltage.

    Thanks,
    Erin