The input range of the SAADC is not as expected.

[TML_YT]

Hellow

We are in trouble. Please tell me what to do.

The input range of the SAADC is not as expected.

I use:
・nrf52840
・VDD=3.3V by Regulator
・nRF5_SDK_17.1.0
・Sample program Unmodified　\examples\peripheral\saadc

Therefore:
・gain=1/6
・Resolution=10bit
・Reference internal =0.6V
-->The Voltage input range should be 3.6v.

Situation & The problem
Vin=1.0V->0x011e (ok)
Vin=1.5V->0x01ab (ok)
Vin=2.0V->0x0239 (ok)
Vin=2.2V->0x024f (NG)
Vin=2.3V->0x01e1(NG)
Vin=2.4V->0x017e(NG)

If the input voltage exceeds about 2.2V, the output code is not as
expected, and if the input voltage is higher than that, the output code
value becomes smaller.

What are the causes and what can be done about it?

Please help me.

[haakonsh]

That's strange. Are you using our DK, or are you using a custom board? 

What's you regulator configuration? 

[TML_YT]

Sorry it took me so long to get back to you. I accidentally clicked on
'verified answer' and couldn't reply.

I use DK of other manufacturers.

And then Regulator conditions in the DK board, as follows
5V→Regulator(3.3V)→nrf52840

As for the DK, it is made by another company, but the other functions
are normal and there does not seem to be any problem with it.
We are also concerned about the fact that similar questions have been
asked in the past and no clear answers have been given.

Is this an unusual situation?

[TML_YT]

Thanks for the reply

I too am beginning to think that the device has been damaged.

(1) Attached is the state of the UICR register.
I loaded the sample program "blinky_FreeRTOS" and monitored it with the view-Registers function of SEGGER. In the SAADC program, the contents of the register are exactly the same.
I hope you can find out the cause from this.

(2) As for SAADC, the result is similar for AIN0 and AIN1.
As for GPIO output, I tried some other ports, but H level was 1.8V as well.

By the way, as for my concern about Erase-All, I asked Raytac about this, and I found that there is no problem in using it.
I still think that the device might have been damaged by the wrong power-on sequence of the evaluation board or debugger, or by static electricity.

Fullscreen blinky_FreeRTOS_pca10056 Registers - 01-3-22 at 08h56.txt Download

UICR                                  
    NRFFW[0]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[1]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[2]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[3]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[4]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[5]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[6]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[7]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[8]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[9]            0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[10]           0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[11]           0xffffffff    
        NRFFW           0xffffffff    
    NRFFW[12]           0xffffffff    
        NRFFW           0xffffffff    
    NRFHW[0]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[1]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[2]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[3]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[4]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[5]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[6]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[7]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[8]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[9]            0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[10]           0xffffffff    
        NRFHW           0xffffffff    
    NRFHW[11]           0xffffffff    
        NRFHW           0xffffffff    
    CUSTOMER[0]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[1]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[2]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[3]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[4]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[5]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[6]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[7]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[8]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[9]         0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[10]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[11]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[12]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[13]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[14]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[15]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[16]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[17]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[18]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[19]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[20]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[21]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[22]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[23]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[24]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[25]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[26]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[27]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[28]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[29]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[30]        0xffffffff    
        CUSTOMER        0xffffffff    
    CUSTOMER[31]        0xffffffff    
        CUSTOMER        0xffffffff    
    PSELRESET[0]        0x00000012    
        PIN             0x12          
        PORT            0             
        CONNECT         0             
    PSELRESET[1]        0x00000012    
        PIN             0x12          
        PORT            0             
        CONNECT         0             
    APPROTECT           0xffffffff    
        PALL            255           
    NFCPINS             0xffffffff    
        PROTECT         1             
    DEBUGCTRL           0xffffffff    
        CPUNIDEN        255           
        CPUFPBEN        255           
    REGOUT0             0xffffffff    
        VOUT            7             

[haakonsh]

REGOUT0 is set to 1.8V. When you apply a voltage of 2.1V and above (1.8V + 0.3V) the ESD diodes will start conducting from the analog input into VDD. If the signal source has more than ~100ohm internal impedance the voltage on the input pin will drop closer to VDD. 

See the I/O pin voltage specs in Absolute maximum ratings. 

[TML_YT]

A series of problems were solved by writing a '5' to the UICR->REGOUT0 register in high voltage mode, setting it to 3.3V.

The output level of the GPIO is now about 3V and the input voltage range of the SAADC is the same as the set value.

However, this register should only be enabled when operating in VDDH mode. The circuit was wired in such a way that it would work in VDDH mode, but the question remains: why?

(1) Then, why was VH=3.3V sometimes observed in the beginning?
The waveform recorded by the oscilloscope at the time was about 3V, so I don't think I'm mistaken.

(2) Also, why the return value of "nrf_power_dcdcen_get();" or "nrf_power_dcdcen_vddh_get();" is "false" in both cases?

I didn't change the power supply, and I didn't apply the current to the regulator to make the voltage drop significantly.Incidentally, the revision for the 52480 was NRF52480_xxAA_REV2.

Do you know the reason for these questions?

[haakonsh]

1. The UICR->REGOUT0 register was likely set to 5(3.3V) at some point, then an nrfjprog eraseall command reset the UICR->REGOUT0 to its default state, 7 (1.8V). 
   
   
2. You check for the state of the DCDC regulators, If false it means that they are operating in LDO mode. 

I hope this clears things up. Most likely Raytac ships their dk's with UICR->REGOUT0 set to 5, we do the same for our nRF52840 dongles. 

[TML_YT]

Thank you for your reply.

I asked Raytac and they said the evaluation board is working with VDDH. And I understood that it is working with LDO, not DC/DC.

I think the trouble is that Raytac shipped with UICR-> REGOUT0=5, but I did an All Erase and it went back to REGOUT0=7.
I think this is why, since All Erase, the board has a GPIO output H level of 1.8V and the SAADC input range is no longer as expected.

Finally, I have cleared things up.
Thank you for all your help and advice.

[haakonsh]

I'm Glad I could be of assitance :)