ADP1712 Enable/Disable Voltage Tolerance

In reference to Figure 30 in the current revision of the ADP1712 datasheet, what type of variation can we expect on these voltages? 

In the following test circuit, we changed R2 to 49.9k and R3 to 16.2k. Using a meter to adjust the supply voltage, I adjust the VIN voltage to 5.01V (as close as I can get with my hand-dial control and hand-held meter measurement) and I measure the voltage at the enable pin to be 1.215V. Assuming zero tolerance on the resistors, we would expect the voltage to be 1.225V when VIN = 5V, but with resistor tolerance and the leakage current into the enable pin, I can understand that being 10mV lower than expected.  What I am scratching my head over is that this does not result in activation of the ADP1712's output.  Based on Figure 30, it would seem like anything above 1.2V would cause activation.  Perhaps my meter is not well calibrated but there is more on this below.

As I increase the VIN voltage, I find that it starts when VIN reaches ~5.25V, result in VEN  = 1.27V according to my meter.

In the next step, I changed R3 to 16.5k and noticed that the device would start at VIN = 4.97V, resulting in VEN = 1.225. 

Taking this one more step, I changed R3 to 16.9k and the ADP1712 enabled the output voltage when VIN = 4.76V, resulting in VEN = 1.202V.

Any thoughts on this? Am I missing anything or could I be dealing with a meter that is out of calibration?

Thanks!

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  • 0
    •  Analog Employees 
    on Jan 28, 2015 6:56 PM

    I took a look at the ADP7102 it looks like a great product!  In this particular case, our primary goal was to power a digital sensor with a supply that reaches 3.3V in less than 100us, so the 800us start-up time in the ADP7102 will not meet this objective.  We will make adjustments to the use of the UVLO function, based on your very helpful insights!  Thanks again for your quick response and helpful insights.

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  • 0
    •  Analog Employees 
    on Jan 28, 2015 6:56 PM

    I took a look at the ADP7102 it looks like a great product!  In this particular case, our primary goal was to power a digital sensor with a supply that reaches 3.3V in less than 100us, so the 800us start-up time in the ADP7102 will not meet this objective.  We will make adjustments to the use of the UVLO function, based on your very helpful insights!  Thanks again for your quick response and helpful insights.

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