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Power Sequencing On Kinetis

Question asked by gcary on Nov 24, 2014
Latest reply on Nov 25, 2014 by gcary

What is the power sequence requirement for Kinetis devices?  The K60 data sheet describes a sequence, but it also has conflicting specs for VDD and VDDA.  Here is what the K60 data sheet says:

K60PowerSequence.png

I don't think the following spec is consistent with the power sequence above:

K60VoltageRequirements.png

It says that VDDA must be within 0.3V of VDD.  The Max spec of VDD + 0.3V makes sense, but not the Min spec, assuming the sequencing spec above is correct.  Maybe it should be VSS - 0.3?

 

To make things more confusing, it seems there is a conflicting requirement as follows:

K60VoltageOperatingRequirement.png

Would someone please explain what these specs mean or what they are supposed to be?  I have compared the K22 data sheet to the K60, and there isn't a power sequencing section like there is for the K60.  But the other specs are the same.

 

Depending upon the answers to my questions above, my next question might not apply.  If I wanted to provide a very low noise supply for VDDA, would the following circuit meet the specs?  The Schottky diode will keep VDDA within 0.3V of VDD when Vin is removed.  Otherwise VDDA will be follow VDD as it rises, until it reaches its regulation voltage of 3.0V.  The LP5907 from TI only costs about 14 cents, and is meant for analog and RF applications.

 

Schematic.png

Another option is a part from Micrel, called a Ripple Blocker.  The part number is MIC94300 (MIC94300 - Linear Power Filters - Micrel). It provides >60dB of noise rejection from 40kHz to 5MHz.  It is an active device with a voltage drop of about 170 mV.  Here is a schematic from the Micrel website:

Micrel.png

The MIC94300 is not very expensive.  Only about 25 cents or less.

 

Thanks,

 

Greg

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