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TMP103: complete shutdown

domenyko
Genius 9655 points
Part Number: TMP103
Other Parts Discussed in Thread: TMP102, TMP108, TMP106, TMP112

Dear all,

one of my customer is using the TMP103 in an application very sensitive to the power consumption. In order to save power the designer remove the power supply to the TMP103 (High side P Mosfet) leaving the I2C pin (SDA, SCL) connected to the bus. In this condition due to ESD protection the device burns more current and at the next power up it does not communicate on I2C bus.

Could make sense to insert a P mosfet also in the SCL and SDA pin in order to completely disconnect the TMP103 from any  voltage ?

I've attached the current solution and the proposal.

regards,

Domenico

  • 0
    TI__Mastermind 35895 points
    Hi Domenico,

    Are you aware that TMP103 consumes half of a microamp when it is configured for Shutdown mode? I highly recommend making use of this feature instead of implementing this circuit.

    That said, are you really using 2N2608 JFET? I was not able to find much information about this device, but it looks like it is only sold in a metal can. It's hard for me to say if there will be any issues with this circuit based on the limited information available.

    While it is true that ESD protection structures on TMP103's input pins will conduct when the potential is greater than V+ pin, I wouldn't expect the device to be damaged by this condition. Note that section 6.1 Absolute Maximum Ratings in the datasheet indicates that the TMP103 input pins cannot exceed voltage on V+. Other I2C devices typically don't have this restriction. TMP103 is unique in this regard due to having only 4 pins.

    If you were to implement a switch, it's important to note that the SDA pin must operate bidirectionally. The V+ and SCL pins should work acceptably with one-way current flow, but the SDA will not.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    TI__Genius 9655 points

    Hi Ren,

    Thanks for the answer. The switch inserted in the schematic was just for highlight a possible solution I did not pay attention to the P/N.

    As you noticed the approach will not work for SDA.

    Can you suggest an alternative temp sensor (small form factor) that can be shutdown (removing the supply) and leaving the I2C bus connected ?

    Is there any chance that the leakage of the current in the SDA and SCL pin in that condition burn more power than the device in shutdown mode ?

    Regards,

    Domenico

  • 0 in reply to domenyko
    TI__Mastermind 35895 points
    Domenico,

    I would recommend TMP108. It is 6 ball WCSP; same pitch as TMP103. TMP106 is an older product in 6 ball WCSP that could be an option as well, but at a larger 0.5mm pitch. For a packaged device, TMP102/TMP112 still sets the standard for smallest.

    We specify input leakage current to be less than 1uA. This is only because it's expensive to measure accurately below that level. This is the same reason why our Shutdown current is 1uA max with a typical value of 0.5, 0.3 or even 0.1uA on some products. They're both just leakage currents, and we can't justify measuring them accurately in production.

    Thanks,
    Ren