Hi,
My customer is using PCA 9518 for their products.（using all channels of HUB）
Although the occurrence frequency is very low, the bus is fixed to Low (about 0.5 V) at power-on.
Q1.Do I need a special power up sequence for the PCA 9518?
Q2.When it is enabled after the power supply startup is completed, the bus voltage goes from low to high.
Is it a valid way to return from abnormal state?
Best regards,
Seishin
Hey Seishin,
"Although the occurrence frequency is very low, the bus is fixed to Low (about 0.5 V) at power-on."
Do you have a schematic we can review, it could be possible the customer may have set up the device wrong. Can you also confirm that all the channels (and EXPXXX lines) have pull up resistors?
If you can post what the Vcc wave form looks like when you power cycle it (particularly when this bug occurs), that may also give us more information.
"Q1.Do I need a special power up sequence for the PCA 9518?"
-Though I have no heard of this device having a specific power sequence you may want to adhere to the power up requirements that some of our other PCA devices require:
"Q2.When it is enabled after the power supply startup is completed, the bus voltage goes from low to high.
Is it a valid way to return from abnormal state?"
-I assume you mean the bus voltage goes from high to low and not low to high. It sounds like if this is something occurring at power on, then it is related to the ramp rate of the Vcc pin or maybe the time off is not sufficient. Another power cycle sounds like the best approach. I would have to see waveforms when this bug occurs to get a better understanding.
Thanks,
-Bobby
