ISOW7841: ISOW7841 breaks down

Prodigy 180 points

Replies: 5

Views: 111

Part Number: ISOW7841

In mass production my customer has met with failures of ISOW7842 . The ISOW goes to short current by second ( ISO ) side.

Could you revise the scheme and suggest the ways to resolve the issue?

There are technical details in attachment:

  1. TOP.png and BOT.png – are PCBs
  2. IMG 20190903……jpg – board’s photo
  3. BldcPmsm.pdf - schematic
  4. BldcPmsm.pdf

5 Replies

  • Hi Andrey,

    Thank you for including PCB images and a schematic. What is the expected load on Viso pins? Is the same unit (DD1, DD12, DD3) failing in each system? What is the voltage level during short conditions?

    1. This may not be the cause of failure, but it is recommended to use a significantly higher decoupling capacitance on Vcc than on Viso. ~100uF higher is preferred, as mentioned in the Power Supply Recommendations (Section 11) of the ISOW7842 datasheet shown below:

    2. If a voltage transient is affecting a pin connected directly to GND or Vsupply, please encourage our customer to use a pull-up or pull-down resistor of 4.7kOhm for these connections, such as for SEL and GND inputs
    3. For emissions improvements, input pins on channels that are not used should be connected to the device's default output state. Since devices in the images appear to be "non-F" devices, unused channel inputs should be connected to Vcc through a 4.7kOhm resistor instead of GND. This is a performance recommendation and not critical for proper device operation.


    I will await your response to the initial questions above.


    Thank you for your time,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hello Manuel

    What is the expected load on Viso pins?   - ~20mA

    Is the same unit (DD1, DD12, DD3) failing in each system?  Yes, It's the same unit.

  • In reply to Andrey Sokolov:

    Hi Andrey,

    Thank you. Is our customer able to add 100uF capacitors in parallel with C100, C79, and C93? Is DD1, DD12, or DD3 the unit always failing in each system? Please also describe the short current condition in more detail.


    Thank you,
    Manuel Chavez

  • In reply to Manuel Chavez:

    "Is DD1, DD12, or DD3 the unit always failing in each system?" - No, one of them unit fails with the same expectance in each systems.

    “Please also describe the short current condition in more detail.” – There is a small resistance (about 0Ohm) between pin 16 and pins 9,15.

  • In reply to Andrey Sokolov:

    Hi Andrey,

    Like Manuel mentioned, the best way to address the issue is to make the total capacitance at VCC pin at least 100µF larger than the total capacitance at VISO pin. Could you please recommend this to customer?

    In addition, I see an issue with decoupling capacitor placement on both VCC & and VISO. The device requires all of the caps to be placed on the same side as device and shouldn't be placed on the other side of PCB. It is also important to keep the smallest value decoupling cap to be placed closest to device pins. Please refer to the below PCB layout from EVM for capacitor placement.

    Let us know if you have any questions, thanks.

    Regards,
    Koteshwar Rao