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LMX2615-SP: Shared SPI bus for two LMX2615-SP

Gilles Aminot
Prodigy 50 points

Part Number: LMX2615-SP

Hello,

I would like to share the SPI bus for two LMX2615-SP parts with Serial Data Output for readback on the MUXOUT pin. Although the datasheet suggests this is possible by setting MUXOUT_CTRL=0 the default setting for this pin is Lock Detect (output). How can I connect MUXout pins together if they are both configured as output from reset? 

Do you have recommendations to prevent damage to both pins while they are mometarily configured as outpus after reset (before they get configured to Tri-State). I considered a series resistor at each pin however I don't know what value to use to minimize damage and still ensure good functionality at the maximum speed of the interface.

Bit Default Desc
MUXOUT_LD_SEL 1 Lock Detect
MUXOUT_CTRL 1 Normal Operation

 

  • 0
    TI__Guru** 120710 points

    Hi Gilles,

    SPI CLK and DATA can be shared but CS must be separated otherwise both device will get programmed at the same time. Suggest have both CS pins pulled-high with resistors or MCU GPIO or SPI interface outputs are default to HIGH state. 

    After reset, MUXOUT of both devices are set to output, and the state is LOW, there is no conflict. It is a good practice to have a series 1kΩ resistor at each MUXOUT pin to limit possible current flow. Given the max. SPI speed is 2MHz for this device, the 1kΩ resistor would not create any signal integrity issue.