MK64FN1M0VLL12 - Using an external voltage reference connected to VREF_OUT pin as the DAC reference.

[seanlaw]

Pg.133 of the K64 reference manual states that for K64 chips, VREF_OUT and VDDA are selectable as the DAC reference. VREF_OUT is the output pin of the internally generated 1.2 V voltage reference. Can an external voltage reference be used as the DAC voltage reference by connecting it to the VREF_OUT pin and selecting VREF_OUT as the DAC reference (with the 1.2 V internal voltage reference disabled)?

[miduo]

Hi,

The VREF_OUT reference voltage can be driven by either the VREF module output (1.2 V) or by an external voltage source applied to the VREF_OUT pin. If using an external voltage source to supply the reference on the VREF_OUT pin, the VREF module must be disabled. When the output buffer of the VREF module is disabled, the VREF_OUT pin is in a high impedance state. VREF_OUT is an optional reference source for the DAC, ADC, PGA, and CMP.

[manfredschnell]

Hi Fang,

we use K64 in our project.

The analog Voltage VDDA is 3,3V.

For ADC we use an external Reference with 3,000V on VREFH / VREFL

We want to use the 3,000V for DAC, too.

Are there any restrictions in voltage level for input "VREF_OUT" ?

--> Is it allowed to Input 3,000V to the switched off output buffer (which is usually 1,2V)?

I found no Information in the datasheet, concerning this.

Best regards,

Manfred

[manfredschnell]

Hello out there ...

is there any NXP employee watching this forum???

I'd like to get an answer to my question about using external REF on VREF_OUT pin.

Best regards

Manfred

[nielsmalotaux]

Hi, Did you ever get an answer or did you find it out yourself?

Regards,

Niels

[manfredschnell]

Hi Niels,

no, I never got an answer...  NXP simply ignores some questions... nevertheless it would be nice to know, if we are in recommended conditions....

In our K64 design we use an external 3,000V reference on VREF_OUT pin. --> It seems to work well.

Best regards

Manfred

[nielsmalotaux]

Manfred,

Thanks for a quick reaction.

Provides hope that we can use the external Vref to drive the DAC ref in our KV31 design.

Will check out to make sure on our board.

Will report you the results.

Niels

[seanlaw]

Excellent, thank you for help with the prompt reply.

Regards,
Sean Law

[manfredschnell]

Hi Sean Law,

did you setup your design with an external reference Input  to pin VREF_OUT?

Can you confirm that's working?

I'm reworking a K64 design and we want to use an external reference for DAC, too.

It would be nice to know.

Regards

Manfred Schnell