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TCAN4551-Q1: Pull down nCS to GND

Part Number: TCAN4551-Q1
Other Parts Discussed in Thread: TCAN4550,

Hello team,

Can I pull down nCS pin to the GND?
There is no other slave device connected parallel to TCAN4551.

If I can, what would be the size of the pulldown resistor?

Best Regards,
Kei Kuwahara

  • Hello Kei,

    No, unfortunately this will prevent the TCAN4550 from valid SPI communication for 2 reasons. 

    First, for error checking, the TCAN4551-Q1 counts the number of SPI clock cycles between the transitions of the nCS signal to ensure there is the correct number of clock cycles for the Read/Write transaction.  If there is an incorrect number of clock cycles, it will report a SPI Error and will discard any SPI Write data. 

    Second, the TCAN4550 will return a Global Status Byte on the SDO pin at the start of all SPI read/write transactions immediately after the nCS transitions Low.

    Therefore, if the nCS pin is hard tied to ground, both of these functions fail and the TCAN4550 will not work.