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SN74CB3Q3257: Signal DC level issue : Pin-14 and 13 shorted together

Part Number: SN74CB3Q3257

We are using SN74CB3Q3257 as aSPI Mux. The B side connected to BMC and CPLD and A side connected to Flash,.

Pin-14 (4B1) and Pin-13 (4B2) are shorted together and used for CS# driven by CPLD (Max10)

We see the logic low is offset to 1.43V (when CPLD Io is LVTTL and 8mA)

The logic low is 1V when CPLD IO is LVCMOS 2mA.

The other signal like CLK, MISO, MOSI driven by CPLD looks okay.

Is there any internal circuit issue with SN74CB3Q3257  which may  not allow shorting to pins ???

  • Shorting B1/B2 pins should be no problem.

    Please measure the voltage at both A and B pins. Is the entire voltage drop of 1.43 V over the switch?

  • Hi Sambit,

    Can you possibly try to re-upload the pictures they didn't seem to show up correctly - I want to make sure nothing is wrong in the schematic. That being said shorting two pins together like that shouldn't present any inherent issue - but a re-upload of the pictures would be great as I can't tell exactly what the issue is. 

    Please let me know.


    Parker Dodson