ISOW7721: ISOW7721F

Hello,

Thanks for reaching out.

I have several questions regarding the testing and information you have provided:

jie liu said:

• INA and INB from low to high at same time, OUTA lags INA by 4.167 ms,  INB and OUTB are synchronized. See FIG1
• INA lags INB from low to high by 1ms, OUTA lags INA by 3.2 ms,  INB and OUTB are synchronized. See FIG2
• INA lags INB from low to high by 5ms, INA and OUTA are synchronized, INB and OUTB are synchronized. See FIG3

1. Are these 3 figures 3 different devices (is figure 1 device 1, figure 2 device 2, etc.)? Is it the same device?
2. I noticed that there were abnormal spikes on the OUTA, EN, and VISOIN. Can you please provide more details on this? It seems like it could be a power supply related issue on the secondary side but some more information would be helpful.
3. Can you please monitor the secondary side 3.3V supply along with the VISO pin and OUTA pin and send a picture of the waveform?
   1. Please also include more information regarding the V/div and time scale.

Regards,
Aaditya V

1. Yes, Same device

2. Pls find the enlarged waveform of FIG1. Secondary 3v3 connect to PIN17_EN_IO2

Hi Jie,

Thanks for sharing the zoomed in picture. 

Assuming the EN pin is directly connected to supply on right side, the inference shown in the image could be the point of concern (see image below). 

This interruption could possibly be causing the channels also see a delay in signals as well. To confirm this, please test again:

1. Please test again and use a separate power supply to power VISOIN and VDD, (not the system power supply on PCB).
2. Please capture waveform of PCB power supply directly to capture any interruption, similar to one shown above.
3. Please also perform ABA swap and test devices:
   1. replace issue device with new device on same PCB to check if issue still happens.

Some additional Questions:

1. How many devices were tested?
2. How many devices have seen this issue?
3. How many PCBs were tested?

This information listed will give us more insight into what exactly is going on and can help us make a better recommendation.

Regards,
Aaditya Vittal

four devices and PCB were tested, and all the devices have seen this issue.

To be honest， three weeks ago, when we found this issue firstly, we also think it is power issue and add another 10uF cap in parallel with C206.

and then test, it also can't work normally. In addition, we found if input voltage more than 700V, this delay will happen. And with the input voltage increasing, the delay time will be long. when input voltage up to 1000V, delay time up to 4ms around. I doubted if there some short creepage and clearance to cause this issue, but actually there is enough as calculation. 

Hi,

Thank you very much for the PCB layout and information regarding 4 devices having issue.

Were you able to do the testing I had mentioned in my last response?

Aaditya V. said:

This interruption could possibly be causing the channels also see a delay in signals as well. To confirm this, please test again:

1. Please test again and use a separate power supply to power VISOIN and VDD, (not the system power supply on PCB).
2. Please capture waveform of PCB power supply directly to capture any interruption, similar to one shown above.
3. Please also perform ABA swap and test devices:
   1. replace issue device with new device on same PCB to check if issue still happens.

Regards,
Aaditya V