CC2640R2F: how to measure ADC Vref (4.3V) ?

Albert Bang

Intellectual 1050 points

Part Number: CC2640R2F

Hi,

Is it possible to measure the reference voltage (Vref) ?

over 6 years ago

0 Albert Bang over 6 years ago

TI__Intellectual 1050 points

0 Fredrik K over 6 years ago in reply to Albert Bang

TI__Guru** 106705 points

Hi Albert,

You can measure the reference by inserting a known voltage on the ADC input. Keep in mind though that the input has to be less than VDDS.

Regards,
Fredrik

0 IUsedToBeARealPerson (M-W) over 6 years ago in reply to Albert Bang

TI__Guru 58425 points

Hi Albert,

You could possibly measure the 1.48 V reference directly, the 4.3 V however is not measurable (in any other way then what Fredrik suggested) as it is an internal scaled reference based on the 1.48 V one. If measuring the 1.48 V one, there is trim values that you would also have to make sure to check and take in to consideration.

Could I ask why you want to be able to measure this value?

0 Albert Bang over 6 years ago in reply to Fredrik K

TI__Intellectual 1050 points

Hi Fredrik,

could you please elborate how to measure the Vref ?

The purpose of this is that Vref is varied per devices so they want to compensate the difference at their manufacture site.

0 Albert Bang over 6 years ago in reply to IUsedToBeARealPerson (M-W)

TI__Intellectual 1050 points

The purpose of this is that Vref is varied per devices so they want to compensate the difference at their manufacture site.

could you please elborate how to measure the 1.48V ?

0 IUsedToBeARealPerson (M-W) over 6 years ago in reply to Albert Bang

TI__Guru 58425 points

Hi Albert,

I will need to get back to you on exactly how to measure this signal. The variation of the Vref between the devices should not be something that impacts your customer and that they need to account for. The Vref value is tuned during manufacturing so that the value are correct when the device is "trimmed" during startup.

0 IUsedToBeARealPerson (M-W) over 6 years ago in reply to IUsedToBeARealPerson (M-W)

TI__Guru 58425 points

Hi Albert,

You can MUX the Vref out to AUXIO7 (DIO23) by performing the following register writes:

    HWREG(0x400C6000) = 0xFF;            /* AUX_WUC:MODCLKEN0:  REQ All */
    HWREG(0x400C6030) = 0x1;              /* AUX_WUC:ADCCLKCTL:  REQ */
    HWREG(0x400CB000) = 0x8;              /* ADI_4_AUX:MUX0:     ADCVREF */
    HWREG(0x400CB007) = 0x1;              /* ADI_4_AUX:MUX4:     AUXIO7  */
    HWREG(0x400CB00A) = 0x41;            /* ADI_4_AUX:ADCREF0:  REF_ON_IDLE + EN */

This will output the 1.48V reference on the pin. Keep in mind that to get an accurate result, you will need to take the trim values into consideration (which is why we have value adjustment functions in the ADC driverlib).

0 Albert Bang over 6 years ago in reply to IUsedToBeARealPerson (M-W)

TI__Intellectual 1050 points

Hi M-W,

could you please explain me more about "trim" in detail ?

even though Vref is tunned during the manufactureing, a variation maybe existed.

could you please share the varation value ?

0 IUsedToBeARealPerson (M-W) over 6 years ago in reply to Albert Bang

TI__Guru 58425 points

Hi Albert,

It is described in the ADC section in the TRM (chapter 17.4.8.1). While the trimmed values are available in the CCFG, you could use the DriverLib helper function to do the adjustments: AUXADCGetAdjustmentGain, AUXADCGetAdjustmentOffset AUXADCAdjustValueForGainAndOffset

The values we have for the ADC is what is available in the datasheet, I don't have any variation values to share.

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CC2640R2F: how to measure ADC Vref (4.3V) ?