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Original question:

ISOW7840: How does the device work if an external voltage source is applied to the Viso pin?

ISOW7840: Out put can't get.....

Vignesh M1
Prodigy 70 points
Part Number: ISOW7840
Other Parts Discussed in Thread: ISOW7841EVM

Hi,

I'm using "ISOW7840FDWER" IC for my testing application.

When i power up the IC it will get heat upto 80D Celsius. I want to know it is the normal heat.

the below test i done in the IC But i did't get O/P.

VCC- 5V DC Feed through a @5V,600mA DC-DC Converter.

Viso and SeL pins are shorted.

In channel 1 (INA-1) feed 5V DC and  with reference to GND1-1.

after the above mentioned steps are complete and then power Up the IC its temperature will increases high.

at the same time i did not get  Output  in channel (IND-1) with reference to GND2-1 in no load condition.

Isolator Circuit.

24V to 5V DC-DC Converter Circuit

Thanks & Regards,

Vignesh M

  • 0
    TI__Mastermind 49445 points

    Hi Vignesh,

    Sorry to hear about the issue.
    80C of device temperature under no load conditions seems lot more than expected. Could you please share the schematic? If the decoupling cap values are not chosen according to the recommendations in Section 11 of ISOW7840 datasheet then it is possible for the device to not operate as expected. Please share the schematic so that I can comment better, thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    Dear Sir,

    Kindly find the Schematic for your reference.

    Is there any external voltage shall i give to the Viso terminal depend upon my requirement voltage.

    Isolator Circuit_v1.1.PDF

    Thanks & Regards,

    Vignesh M

  • 0 in reply to Vignesh M1
    TI__Mastermind 49445 points

    Hi Vignesh,

    Thanks for sharing the schematic, this helps.

    I see that there are two ISOW7840 devices used in your schematic. Both devices are powered from the same 5V source and have necessary decoupling capacitors of 10µF + 0.1µF which is good but I do not see any decoupling capacitors for the output VISO pins in the schematics. Since ISOW is a DC/DC converter, it needs to have necessary decoupling capacitors for the device to function normal. This should be the reason for device not working in your case..

    Please use 10µF + 0.1µF decoupling capacitors for VISO as well, as also suggested in device, without which we do not expect the device to function properly. These capacitors also need to be within 2mm distance from device pins, as suggested in datasheet layout guidelines section.

    Once you incorporate the capacitors and test your board, please let me know the results. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    Hi,

    Okay will check and let you know. 

    As per your words the Viso side decoupling capacitor is not connected so that the device getting heat and also the o/P is not come . 

    After connecting decoupling capacitor in Viso side any external voltage feed to Viso?

    pls refer the image...Figure No:33

  • 0 in reply to Vignesh M1
    TI__Mastermind 49445 points

    Hi Vignesh,

    Thanks for confirming that you will be using the decoupling capacitors at the output and test again.
    Regarding the test circuit you have shown, please note that the circuit is a CMTI test circuit and not to be considered as an application circuit. The CMTI test circuit is a generic circuit showing the typical connection for CMTI tests and indicating the voltages that were set. For ISOW, only VCC needs to be supplied while VISO is internally generated.

    An example application circuit has been provided in Figure 38 in section 10.2 of ISOW7840 datasheet. Alternatively, you can also refer to ISOW7841EVM schematic.

    Hope to hear from you after you test your circuit with output decoupling capacitors used, thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    Hi,

    As per your words connected the Decoupling capacitors in Viso the IC working fine. 

    Is there any procedure  to check IC in healthy condition??. Why because Earlier i power up the IC without Decoupling  capacitors in Viso at the time it generates heat upt 80C.

    Now i connected the same IC with decoupling capacitors in Viso but the out remains 0V. I think the IC gone.

    Regards,

    Vignesh M

  • 0 in reply to Vignesh M1
    TI__Mastermind 49445 points

    Hi Vignesh,

    If the damage is significant then it will show up in device operation and testing the device to check if it is producing output correctly and if data is being transmitted correctly. If the damage is minor then it might not be easy to detect.

    Hence, I recommend discarding all devices that are tested with the not optimized original schematic. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    Hi, 

    As per your words i Did the channels are working fine.

    i have one more doubt. in that IC (ISWO7840) the GND 1 & GND 2 is shorted means  the IC will working fine or not ??

  • 0 in reply to Vignesh M1
    TI__Mastermind 49445 points

    Hi Vignesh,

    ISOW7840 has two sections of circuit, there is side1 referenced to GND1 and there is side2 referenced to GND2. The two circuits are isolated and can have a potential difference of upto 1kVrms. This means that whether the voltage difference between GND1 and GND2 is 0V (short) or 1kVrms, the device is still going to work fine and all datasheet parameters are met.

    Please do also note that the purpose of using ISOW7840 would be to provide isolation in system from components on GND1 to components on GND2. If you short these two nodes, then there won't be any isolation in system any more. I hope that answers your question. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 70 points

    Hi,

    yes, i got answer form you.

    Thank you so much sir,

    regards,

    vignesh M