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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.

    Regards,

    Jonathan