Is it possible to connect VREFH to 0V on the Kinetis KE15Z family?

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Is it possible to connect VREFH to 0V on the Kinetis KE15Z family?

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MarcoAEE
Contributor II

Hi,

i'm using a MKE15Z128VLL7 with available VREFH pin. VREFH will be connected to a 4.096V shunt precision reference (LM4040).
I have to create a project that allows the system to be brought to an ultra low power condition. For this reason, when I put the MCU to deep sleep I would like to turn off all peripherals including the shunt precision reference. Essentially there will be a battery supplying the 5V to the MCU VDD pin and shutting down the 5V that goes elsewhere.
From datasheet it shows that the minimum voltage of VREFH is 2.5V, I wonder if for some reason I can damage the MCU if I bring it to 0V.

Datasheet:

MarcoAEE_0-1683820664240.png

Thank you

Marco

 

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Miguel04
NXP TechSupport
NXP TechSupport

Hi @MarcoAEE 

It is not recommended to use values different to the operating conditions.

Best Regards, Miguel.

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bobpaddock
Senior Contributor III
Removing power from the module effectively puts an unknown impedance on the internal bus. Current levels can go up.

A couple of diodes to drop the voltage lower than 4.096 might work to have the pin having some voltage when the system is powered down. Check that the difference between Vdd and VRefH doesn't get violated.
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MarcoAEE
Contributor II

It's an interesting solution. But using shunt reference voltage like LM4040 it have relatively high quiescent current even if the voltage is lower than the reference voltage

I'm considering using a nano power reference voltage like REF35 that has a quiescent current below 1uA

Thank you

Marco

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bobpaddock
Senior Contributor III

I was assuming the 4040 was still having its power removed when in shutdown state.
Obviously needs isolated from the diode idea too.

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MarcoAEE
Contributor II

Adding the diode in series to the reference voltage makes it meaningless. This is because the quality of the reference is subject to the fall of the diode and therefore not very precise and accurate

Thank you

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bobpaddock
Senior Contributor III
Obviously. Sadly text is a poor substitution for a schematic.
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Miguel04
NXP TechSupport
NXP TechSupport

Hi @MarcoAEE 

It is not recommended to use values different to the operating conditions.

Best Regards, Miguel.

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