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LM95172 Not Responding

Bryan Staton
Prodigy 20 points

I am trying to use the LM95172 on a new design but can't get it to respond.  I have the LM95172 connected to a PIC24 with the MOSI going through a 10K resistor and the MISO jumpered together.  I have enable the SPI peripheral and wait 3 seconds.  I then clock in 16 bits by sending 0x00.  I expect the device to send the temperature value during these 16 clock cycles, but it appears that the LM95172 is pulling the SI/O line low.  I see the PIC24's spi signal on its side of the 10K resistor but not on the LM95172 side.  I read somewhere that it need to have the power come up in less than 5ms.  I checked mine and it was around 8ms.  After changing some resistor values I got the power supply to come up in about 2.3ms but still no response.  I am on my second chip and have not got any values out of them.  Does anyone have any suggestions?  Please let me know if any more information is needed

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1321.schematic.pdf

  • 0
    TI__Expert 4905 points

    Hi Bryan,

    I looked at your schematic and it looks to me as though the SC pin of the LM95172 is not cannected to anything is that correct? The SC pin needs a clock. Also the first photo is a bit confusing for us can you please label the traces. Where do R39 and R40 connect.

    Thanks,

  • 0 in reply to Emmy Denton
    Prodigy 20 points

    From top down the first four lines are; clock, MISO, MOSI, Slave Select.

    The SC is connected, It is a line going across the page and did not show up on the print-selection. Sorry for the confusion, but that is not the issue. 

    I got the chip to work by putting it on its own SPI bus.  It appears that the MISO was being loaded by some flash memory.  The memory states that they only have a leakage current of about 5uA, but any time they are on the same line with them I do not get a pulse out of the LM95172.  Other device work on the same SPI as the flash memory.  For now I separated it from the other devices to qualify them at temperature for the company I work for.  I will later come back to the issue of them being loaded down so easily.  If they are that sensitive then I will not be implementing them in the next design. 

    Thanks

  • 0 in reply to Bryan Staton
    TI__Expert 4905 points

    Hi Brian,

    We must have adifferent schematic. Can you please mark up the one you attached previously and reattach.

    Thanks,

    Emmy