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

Prodigy 40 points

Replies: 7

Views: 85

Part Number: ISOW7840

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

  • 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

  • In reply to Koteshwar Rao:

    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

  • In reply to Vignesh M1:

    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

  • In reply to Koteshwar Rao:

    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

  • In reply to Vignesh M1:

    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

  • In reply to Koteshwar Rao:

    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

  • In reply to Vignesh M1:

    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