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Original question:

LDC3114-Q1: Power supply recommendations for LDC3114 - Zener diode as voltage regulator

LDC3114-Q1: Power consumption questions

Arthur Thompson27
Expert 1760 points
Part Number: LDC3114-Q1
Other Parts Discussed in Thread: LDC3114, LP3990

Hi, I have a couple questions about LDC3114 power consumption.

1: The LDC3114 datasheet Page 1 shows "One button: 6 µA at 0.625 SPS"  while Page 5 shows "Standby supply current" typical 7uA, max 22uA.  Is it true that somehow the current consumption while sampling one button is actually less than the current consumption in standby mode?  Can you explain which configuration settings are leading to the lowest possible current consumption?

2. The LDC3114 EVM uses an LDO, LP3990, that draws significantly more quiescent current (~43uA) than the LDC3114 uses in these low power modes.  I think if we are interested in the low power performance of the LDC3114 it would be wise for us to choose a different LDO.  I did not see any power supply noise rejection, PSRR, or other LDO selection requirements in the 3114 datasheet.  Can you share any tips on how to select an LDO, or if there was a special feature of the LP3990 that made it a good fit for the EVM?

  • +1
    TI__Mastermind 18545 points

    Hello, 

    The typical current consumption listed on page 5 covers all variation over temperature but the 6uA is most likely referring to room temperature testing. Figure 6-8 shows the change in the standby current over Vdd and for different temperatures: 

    If you want to estimate the current for your implementation, you can use the equations in section 8.1.12 or use the LDC-DESIGN-TOOLS spreadsheet to calculate this for you based on your sensor designs. 

    For the LDO, there is no special requirement that made the LP3990 the choice for the EVM. Anything that can supply enough current for the LDC3114 and any other 1.8V components you have will be sufficient. Be sure to keep in mind the LDC3114 highest sensor channel current (Iactive in the equations above) when selecting an LDO. For PSRR, any noise on the power supply can potentially couple into the device measurement but there is no specific minimum or requirements we have for this part. 

    Best Regards, 

    Justin Beigel