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ISOW7841A-Q1: ISOW7841AQDWEQ1

Siddharth Sangam
Intellectual 640 points
Part Number: ISOW7841A-Q1
Other Parts Discussed in Thread: ISO7841

Hello,

1 : Need to calculate the power dissipation of Isolation buffer. We require the output isolation side current consumption at 10mbps speed.
     Please provide the data, it is not present in datasheet.
2:  Need efficiency vs  isolated side output current.

with regards
Siddharth S.

  • 0
    TI__Guru 54725 points

    Hi Siddharth,

    Thank you for your interest in ISOW7841A-Q1. Please see my inputs below,

    1. I believe you are requesting for current consumption data of the I/O channels independently on the VISO side. This value is not much significance as the current to these channels is going to be sourced from the VCC side. This ICC current for 10Mbps datarate of all channels with CL = 15pF is given in datasheet section 7.10 as 24mA assuming no external load on VISO pin.
      1. If you still need to know current consumption data for I/O channels independently on the VISO side, then you can refer to the digital isolator ISO7841 ICC2 values given in section 6.10 of the datasheet as an approximation.
    2. I am assuming you are referring to efficiency plot against external load on VISO pin. This data has been provided in Figure 6 in section 7.22 of ISOW7841A-Q1 datasheet.
      1. If you meant to request for efficiency plot against the current consumption of I/O channels on VISO side, you can still use Figure 6 with the ICC2 values of ISO7841 as an approximation.

    Let me know if you have any questions, thank you.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 640 points

    Hello 

    1: Need to understand below highlighted part. What is it means PD1 (side 1) and PD2 (side 2).

    2:Need to know operating supply current of secondary side.

    3: Previously we were using ISO7741FQDWQ1 SOIC 16 which was having thermal resistance junction to ambient as 83.4degC/W and now were are using
        ISOW7841AQDWEQ1 with same package and thermal resistance junction to ambient as 56.8degC/W. How is this considered for 2 different IC's with same package different thermal resistance junction to ambient.
       Whether ISOW7841AQDWEQ1 have exposed pads.  

  • 0 in reply to Siddharth Sangam
    TI__Guru 54725 points

    Hi Siddharth,

    Please find below my inputs, thanks.

    1. PD1 and PD2 are the maximum power dissipation ratings of the device ISOW7841A-Q1 on side1 and side2 of the device, respectively. Like all other TI reinforced isolators, ISOW also incorporates two die inside the device, the one on the left is referenced to GND1 and we call it side1 and the one on the right is referenced to GND2, calling it side2.
      1. Please refer to Figure 26 of the datasheet to understand which functional blocks of device lie on side1 and which ones on side2. The two die separation is indicated in the block diagram by the two dashed vertical lines.
    2. Like I mentioned earlier, the operating supply current of the secondary side (side2) data channels is going to be exactly similar to ISO7841 ICC2 current.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 640 points

    Hello Sir,

    Thanks for information.But still need to understand some points.

    1: If efficiency of the device is considered as per datasheet as 53%. How would this power dissipation included in calculation.
    Below is the total power dissipation I have calculated.

    Can you verify above calculations and please provide inputs.

    2: How to calculate power dissipation of side 1 and side 2 individually.

    with regards,

    Siddharth S. 
      

  • 0 in reply to Siddharth Sangam
    TI__Guru 54725 points

    Hi Siddharth,

    Please see below my inputs, thanks.

    1. The equations that you have derived are accurate.
    2. Did you mean to refer to calculating side1 and side2 power dissipation of the DC/DC converter only? I ask this because the equations you have derived already allow you to calculate primary and secondary data channels power dissipation independently. i.e., PD_U2_isolator_primary and PD_U2_isolator_secondary.
      1. Regarding the DC/DC power dissipation split between primary and secondary, I am afraid it won't be feasible to split this dissipation between primary and secondary of the DC/DC converter.
      2. I will still check if I can find a way to provide an approximation of this split, please allow me to come back and let you know.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 640 points

    Hello Koteshwar sir,

    As power dissipation limits are divided in section 1 & 2 we need to cross check if are within limit or not,
    & for that we may need to know distribution of DC to DC loss.Please let us know the detail calculation's consideration.

    with regards,
    Siddharth Sangam.

  • 0 in reply to Siddharth Sangam
    TI__Guru 54725 points

    Hi Siddharth,

    Thanks for clarifying your need.
    I confirm that the power dissipation split between primary and secondary of DC/DC converter is going to be equally split, i.e., 50-50 split. This is also the reason the power dissipation limit split PD1 & PD2 are also equally split as 0.51W. I hope this answers your question, thank you.

    Regards,
    Koteshwar Rao