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TMP464: remote read 256

Part Number: TMP464

NPN is MMBT3904LT1-D. The readout of all four external NPN tubes is 256.can you h温度TMP464.pdf  ave some suggestions?

  • Hi,

    It looks like you are getting the 32.37C on the local channel and on your first remote channel a -256C reading.  This is usually an indicator that your remote has a short. See 7.3.4 Sensor Fault section in the datasheet.

    Can you please check to make sure the D+/D- pins are not shorted together?


  • 1.D+/D- PIN are not shorted.Can you have other suggestion?

    2.The current of the driving transistor is 7.5uA, 120uA, how is this set, is it automatically adapted according to the device parameters or other?

  • Hi,


    This reading can also be a indicator of an OPEN.  can you read the Remote channel OPEN Status register to see if you are getting an OPEN fault? 

    It looks like D1+ is going to "CPU_THMD_CPU_P" could you please send me the schematic or more detail that is past that  net connection?  Looks like it goes to a CPU thermal diode.  Do you know the N-Factor and Beta of that thermal diode?

    Lastly, would you be able to send me oscilloscope shots of the D+ pins?  Please make sure they are zoomed in to see the different current levels.  


    The applied currents of 7.5uA and 120uA is automatically set and driven by the device and cannot be changed.  


  • We read out 256 (1000 0000 0000 0000), in fact, 464 thinks that the external device has short, read 464 0x23 sense fault register
    The RxOP bit value of 256 is 1. After reading RXOP once, the read temperature is normal.

    Why does 464 think that the external line is abnormal,

    About FAULT When we have an exception, except that the built-in temperature reading of the TMP464 is normal, the reading of the other four external NPN tubes is all 256, so this is a bit strange.

  • Hi,

    Just to clarify after a read of RxOP once the device reads all the remotes correctly?

    Can you please send oscilloscope shots of D+ pins? 

    If the D+ pin exceeds around V+ - 0.3V then this will indicate an open circuit.  Something my be causing this to happen causing the fault. 


  • Can you have other   suggestion? Thanhs

  • HI,

    Are you not able to send oscilloscope pictures?  It necessary to see what is happening on the device when you are getting the incorrect reading.

    I also would like to clarify after a read of RxOP once, the device reads all the remotes correctly?


  • Thanks for your help.  There is a phenomenon at present.

    This problem is related to the abnormal termination of chassisd when tmp464 temperature is obtained.
    If the access to tmp464 channel temperature operation is abnormally terminated, the corresponding channel bit in the Remote Channel Open Status Register will be set, indicating that the channel is an open circuit. When this state is reached, the chassisd will visit again next time. An outlier, if the channel bit of the register is cleared and then accessed, the correct temperature value is obtained.
    The current modification method is to obtain the value of the Remote Channel Open Status Register register and obtain the channel-related status when acquiring the channel temperature of the tmp464.

    Why is this happening, do you have a good understanding of this mechanism?

  • Can you please send me the oscilloscope transaction of what you mean by "If the access to tmp464 channel temperature operation is abnormally terminated"?  The Open bit should only be set if the remote channel does not have anything connected to it. 

    Can you also explain what you mean by "chassisd"?


  • Hi,

    Is there any update with the oscilloscope transaction?  I will need to see how the abnormal termination is done to further assist.


  • Hi,

    I am closing post, plesae feel free to open new post if you need further assistance.