topic Re: Power Sequencing On Kinetis in Kinetis Microcontrollers

Power Sequencing On Kinetis

gcary — Mon, 24 Nov 2014 23:51:40 GMT

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:

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

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:

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.

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:

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

Thanks,

Greg

Re: Power Sequencing On Kinetis

apanecatl — Tue, 25 Nov 2014 20:43:15 GMT

In the first table VDDA minimum value (VDD -.3) assumes VDD= 0; the figures depicted in that table correspond to the maximum operating conditions whilst the figures depicted in the second table correspond to the normal or typical operating conditions.

Re: Power Sequencing On Kinetis

gcary — Tue, 25 Nov 2014 21:13:37 GMT

Hi Pedro,

Thank you for clarifying the meaning of those tables. In my opinion, Freescale should use the same wording as every other semiconductor company does. The first table should be labeled "Absolute Maximum Ratings", or even "Maximum Ratings". I would have understood right away then. Now it is clear to me, though the tables are in direct contradiction with the power sequencing order. Obviously if the tables are correct then my circuit ideas would not be advised.

Thanks!

Greg