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TLA2518: SPI Bus Loading

Bryan Robertus
Prodigy 10 points
Part Number: TLA2518
Other Parts Discussed in Thread: SN74LVC1G125

I'd like to connect 10 TLA2518 devices to a a single SPI bus.  The datasheet does not specify pin capacitance or max load capacitance for the SDO pin. 

Should I buffer the SDO pin with a SN74LVC1G125 gated by the CS_L input?  

How fast can I run the bus without the buffer?

Thank you,

Bryan

  • +1
    TI__Mastermind 25020 points

    Hello Bryan,

    A good estimate for pin capacitance is 3pF.

    From what you shared, I gather that even though all 10 devices will be connected to the same SDO transmission line, and  will not transmit at the same time. In this case, I am assuming that the CS will be high for the other 9 devices not transmitting data, meaning the digital pins will be in high impedance mode. In this case the device should not worry about driving these. 

    I would recommend a series resistor on the digital bus transmission lines near the output pins to help with long transmissions lines. 

    The highest the bus can operate is based on the clock frequency, which max rate is 60Mhz. 

    Regards

    Cynthia