Is this a possible Leakage current problem

[FreshmanNewbie]

I have a question about the connection circuit between µ-controller and KSZ8851SNL.



Are the CSN and SO pins of the KSZ8851SNL tolerant inputs? When Q1 is off, LAN3.3V was 0.9V in actual measurement. I think this is due to the current flowing through the internal protection circuit of KSZ8851SNL from the pull-up resistors of CSN and SO. In this case, is there any problem with the design?

 

[KlausST]

Hi,

You say protection diodes... I doubt it has protection diodes input_to_VDD. Please check on this.

You ask about (leakage) currents.
So why don't you use a DVM and measure the voltage across each 100 Ohms resistor? Then you don't need to guess anymore, you can be sure.

On the other hand: When the datasheet says you should not drive input signal when VDD is not applied, then you should follow the datasheet.

Klaus

 

[betwixt]

Move the pull-up resistors to the switched side of the supply and tri-state the SPI lines (or drive them low) when not used.

Brian.