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TMP275: TMP275 - ALERT Configuration, when activ?

Lukas Dangendorf
Prodigy 30 points
Part Number: TMP275

Dear Support,

I'm working with the temperature sensor "TMP275". We use the ALERT Pin for toggle a device on or off by reaching a negative temperature value in T(high). After the device reach the T(low) value it turn on and we make a default configuration for the sensor to read default temperature. In this state we change polarity so the failure occurs, that the device shut down once more. The question is now:

When will be the ALERT configuration enable? If i change the default configuration sequence from:

write configuration
write T(high)
write T(low)

to:

write T(high)
write T(low)
write configuration

it seems to be working..

Hope you can help me!

Best regards

Lukas

  • 0
    TI__Guru**** 244380 points
    Hello Lukas,

    For the TMP275 the Alert pin configuration is enabled by default configuration. Depending on the mode and polarity the output should work as expected. What is the value for Thigh, Tlow and Configuration register that you are programming in the failing and working sequence?
  • 0 in reply to Amit Ashara
    Prodigy 30 points

    Good Morning,

    first thanks a lot for your fast replay. The startup default configuration for the TMP275 is

    max resolution

    Thigh = 60°C

    Tlow = 50°C

    all other are "0" (comparator mode, polarity flag = "0" default)

     

    If the temperature equals or is lower than 10°C i change:

     

    Thigh = -20

    Tlow = -15

    Polarity Flag = "1"

    For tests i use  "Freezer" for cool down the sensor. The device will shut down and starts by -15°C again. For reading the first temperature i configure the sensor to my default values.

    So i checked out that if we configure the configuration register before i set the thigh and tlow values again to the default values  the sensor toggle the alert pin again (checked by oscilloscope). I use debugger to analyze that if the configuration is send to sensor the device shut down again.

     

    The configuration in failing sequence:

    1. Transmission

    i2c_start

    i2c_address

    I2c_setpointer

    i2c_write(configuration)

    i2c_stop

     

    2. Transmission

    i2c_start

    i2c_address

    I2c_setpointer

    i2c_write(Thigh)

    i2c_stop

     

    3. Transmission

    i2c_start

    i2c_address

    I2c_setpointer

    i2c_write(Tlow)

    i2c_stop

     

    The configuration in working sequence:

    2. Transmission

    i2c_start

    i2c_address

    I2c_setpointer

    i2c_write(Thigh)

    i2c_stop

     

    3. Transmission

    i2c_start

    i2c_address

    I2c_setpointer

    i2c_write(Tlow)

    i2c_stop

     

    1. Transmission

    i2c_start

    i2c_address

    I2c_setpointer

    i2c_write(configuration)

    i2c_stop

     

    The question is now, why the device is shutting down then i will write the configuration before setting up the min./max. values for temp-registers. Maybee it is caused by writeing the default polarity?

    Best regards

    Lukas

  • 0 in reply to Lukas Dangendorf
    TI__Guru**** 244380 points
    Hello Lukas,

    When operating the device why is the Thigh being made -20C and Tlow being made -15C. It should be the other way around, i.e. Thigh be -15C and Tlow be -20C. So that way when it Tcurr < Tlow the Alert pin will be high and when Tcurr > Thigh the Alert pin will be low.
  • 0 in reply to Amit Ashara
    Prodigy 30 points

    Hi Amit,

    thank you very much for your helpstition, it works! :) Maybe you can help me with my further question about when the configuration becomes active in the sensor. If i transmit the configuration data to the sensor, what's the trigger for: "Now the sensor will work with the new configuration"?

    Best regards

    Lukas

  • 0 in reply to Lukas Dangendorf
    TI__Guru**** 244380 points
    Hello Likas

    The I2C transaction once completed with "STOP" condition on the bus, should be the trigger for load of the new configuration. As an example you can keep the device at a known temperature and then load the Thigh or Tlow register with a value that should cause an Alert. Measure the time delay from the Stop to the Alert going active.

    Some setting of the I2C Configuration may have to wait for the Temp Value to be converted like conversion rate, fault queue. I hope that helps.