MIMXRT1160 ADC VREFH configuration

[Dee_m]

This is regarding VREFH connection for i.MXRT1166

Following are excerpts from the reference manual:

• 86.1.4 LPADC voltage reference options
  The LPADC supports the following voltage reference options ADCx_CFG[REFSEL]:
  • 00 - VREFH - connected as the primary reference option
  • 01/10 - VDDA_ADC_1P8 - connected as the alternative reference option
  • 11 - Reserved
• 86.3.2 Voltage reference
  The voltage reference (VREFH or VDDA_ADC_1P8) used by the LPADC is supplied from
  either an on-chip voltage reference source or from an off-chip source supplied through
  external pins.

Is the VDDA_ADC_1P8 internally connected to the VREFH somehow? If so, no external connection would be required for REFSEL = 01/10.
What is the specification for internal voltage reference? What is the voltage accuracy?

Or we need to connect VDDA_ADC_1P8 separately? Then what is the significance of REFSEL = 01/10? (as VREFH is then supplied externally and REFSEL = 00). The MIMXRT1160-EVK connects VDDA_ADC_1P8 to VREFH.

Thank you.

[Dee_m]

Thank you for the reply.

Thus, REFSEL = 01/10, is for using an external voltage reference connected to VREFH_pin (G16).

Then what is REFSEL = 00? Is there an internal reference? If so, what is the value of it? Where can I get its specification?

[kerryzhou]

Hi @Dee_m ,

  No, you misunderstand it.

00 is VREFH,

01/10 is the VDDA_ADC_1P8 external reference.

In fact, both VREFH and the VDDA_ADC_1P8 is the external reference.

Wish it helps you!

Best Regards,

Kerry

[Dee_m]

I am still not clear.

This means,

REFSEL = 00 : The source connected to VREFH will be used as reference.

REFSEL = 01/10 : VDDA_ADC_1P8 (connected to K15) will be used as reference. Here, VREFH can be left unconnected.

Please correct my understanding.

If this is the case, then REFSEL = 00/01/10 would lead to the same reference for the 1160-evk.

[kerryzhou]

Hi @Dee_m ,

   Thank you for your updated information.

  Please check the datasheet:

It will be more clear!

To the EVK, yes, you are right, both VREFH and the VDDA_AD_1P8 is 1V.

This hardware design it like that.

But, to the RT1170 chip, you can modify the VREFH to the above range 1V to 1.89V.

Then the 00,01 input reference is different.

Wish it helps you!

Best Regards,

Kerry

[kerryzhou]

Hi @Dee_m ,

    VDDA_ADC_1P8 is the external pin, not the internal pin connected to the VREFH.

So, if you want to use this 1.8V, you need:

connect VDDA_ADC_1P8 separately. Then configure REFSEL = 01/10.

Wish it helps you!

Best Regards,

kerry