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ISOW1044: ISOW1044 VDD supply

Venkata Pavan Kumar Palakurthi
Prodigy 10 points
Part Number: ISOW1044
Other Parts Discussed in Thread: LMR38010

Tool/software:

Hi,

We are facing an issue with ISOW1044 for one of our application. The CAN communication is not happening with VDD 5V and VIO 3.3V. But it works for VDD 3.3V and VIO 3.3V. 

Our Input voltage is 48V.

5V power is from DC-DC LMR38010 and 3.3V power is from TPS7A2633DRVR. 

STB pin is controlled from micro controller and it is driven low.  

VISOIN and VISOUT are measured as 5V in both the cases. 

Adding the images of schematic and power up scope wave forms with VDD 5V and VDD 3.3V

VDD 5V

  • 0
    Prodigy 10 points

    CH1 is VDD

    CH2 is VIO

    CH3 is RX

    CH4 is TX

  • 0 in reply to Venkata Pavan Kumar Palakurthi
    TI__Guru 53685 points

    Hi Venkata,

    Thank you for reaching out. I have reviewed the schematic and I have the following concerns.

    1. The decoupling capacitors (C1009 & C1010) on GND1 pin are currently connected after the ferrite bead (L1001). The device should see decoupling capacitors on their pins directly, i.e., VDD and GND1 pins should have the capacitors connected to their directly.
      1. Failing to do this can limit the current into device and affect device operation.
      2. Ferrite bead (FB) should be used after the decoupling capacitors and before connecting to the system.
    2. Similarly, capacitors (C1000 & C1001) are connected to VIO directly but are not connected to GNDIO directly. These should be connected to device pins directly and then filtered using ferrite beads.
    3. EN/FLT pin is currently left floating, although this is okay for laboratory test conditions, it is recommended that the pin is pull-up using a pull-up resistor of 4.7kΩ or higher.
    4. On the secondary side, there is an FB (L1002) between GND2 and system ground but there is no FB between VISOOUT and VISOIN. This is not mandatory but is needed for filtering device switching noise.

    From the waveform you have shared, I couldn't make out any issues in those waveform as TXD and RXD are matching. Could you please share waveform where there is communication issue? If TXD and RXD are matching all the time then there might not be an issue with ISOW1044 and the issue could be related to the software implementation or elsewhere on the PCB.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    Hi Koteshwar Rao,

    Thank you for reviewing the schematic.  Removing L1001 and shorting solved my issue.