PCA9306: Enable the translator causing swing on Vref1

Hi Michael,

Thanks for quick support and sorry for late reply. I understand that a 200k pull on Vref2 is essential, and I will add to a system. Just have a question for converting 5V logic to 3.3V 

is Vref2 will be 3.3V and Vref1 will be 5V basically which is in or out. 

Thanks

Hi Michael,

Thanks for the quick reply, does below schematic even works to convert logic or do you have any alternative translator that can work for 5V to 3.3V

Thanks

Hi Michael,

Sorry for late reply. But we have relieved our new board and still we have same issue, the 3.3V is swinging. Did I do something wrong?

Same schematic as previous send  you.

Thanks

Hi Amir,

Do you mean the power supply or the I/Os? 

Furthermore, if 3.3 V supply is noisy and 5 V supply is not, change C63 to 100 pF to verify, thanks.

Best Regards,

Michael.

Hi Micheal,

Thanks for the Reply. The 3.3V is swinging and cannot keep voltage regulate to 3.3V and become 3.5- 3.8V. As soon as you turn off the enable on level shifter 3.3V work perfectly. Even after changing C63 to 100pF the 3.3V cannot keep steady. 

Thanks
Amir 

Hi Amir,

I suspect you are referring to the 3.3 V power supply. Please use a different / cleaner power supply (with proper grounding) to verify issue is not associated with power supply. If noise persists, you may also try reducing R42 similar  to 8.1.8 of the data sheet, thanks.

Best Regards,

Michael.

During normal operation, a small current flows into VREF2 and out of VREF1. If the 3.3 V supply cannot sink this current, its voltage will float up.

Add a ≤ 470 kΩ resistor between VREF1 and GND to get rid of the current.