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Lowest possible power consumption for "sampled" LDC1614 use

Other Parts Discussed in Thread: LDC1614

Dear all,

I have a VERY power critical application where I use a LDC1614 ( possibly 1612 is sufficient ). I "only" need 100 measured values per second.

What is the best way do do that as power - efficient as possible ?

- Put LDC to "sleep" via config register in the "pauses " ?
- Use the SD pin to power down the entire thing? But Startup time is so long ( 2msec + register setup time ) that likely the "sleep"  approach overall is more efficient.
- Can I just halt the clock input to save power ?
- Any advice for a low power clock source ? The usual crystal oscillators in the 20MHz-ish range all consume 7-9 milliwatts which is way too much. Using a 32kHz Xtal and a PLL ?
- Does the LDC power consumption scale with clock frequency ? Thus, does it save power to use the lowest possible clock frequency and set the clock dividers to 1 ?
- Is there a "single shot" mode to just do one measurement ?
- Is the I2C interface power requirement significantly depended on I2C speed ? ( I assume not, therefore faster is more efficient.. )

Thanks,

   Wolfgang

  • Hi Wolfgang,

    We have a power consumption estimator on the LDC tools spreadsheet (www.ti.com/.../slyc137) which can help.

    Regards,

    ChrisO
  • Chris, thanks for the reply. This Current Consumption Estimator could use a few lines of explanation.

    E.g. based on the current consumption numbers that thing spits out and how they change if I change parameters like CLKIN frequency, I *ASSUME* the result is the -AVERAGE- current consumption over time of you enable the LDC just for the measurement ?

    There is a "samplerate" field. How is this to be understood ? Is this meant to be the rate at which I activate and de-activate the LDC ? Or IS there a "single shot" mode in LDC ( I asked that before ).
    Or do I create a DIY single shot mode by the sequence: Get LDC out of sleep, wait for DRDY to become active, read the data, put the LDC back to sleep ?

    Thanks,

    Wolfgang

  • Chris, I now read the DS 3 times and still do not 100% get it.
    Page12 states that the ENOB is defined by CHx_RCOUNT register. So, it seems the LDC counts f_sensor cycles for a time defined
    by f_ref x 2^RCOUNT ? It seems to be like this because the conversion time is proportional to the ENOB's in the excel tools.
    But then, with RCOUNT being a 16 bit register, how can I get more than 16 ENOB's ?