ADS1263: ADS1263IPW need help

hi,Chris,

First, thank you for your answer.

1.   Yes, the(ADC1) AIN2 channel sampling value is always full-scale when external reference input is 2.5 V.

2.   When using internal reference voltage, (ADC1)AIN2 channel sampling is normal.

3.  The (ADC1)AIN2 input voltage range is 0~2.5V.

4.  The initialization configuration is as follows:

void  Initialization_ADS126xREG(void)       //单个写ADS1256寄存器
{      
 
   ADS126xSendStopCommand();
   ADS126xSendADC2StopCommand();
   delay_us(100);  
   ADS126xSendResetCommand();    //复位、校准
    
    Reg_data[0]=0x03;//使能内部参考,取消内部电平输出
    //Reg_data[0]=0x02;  //取消内部参考
    ADS126xWriteRegister(0x01,1,Reg_data);   //power REG ref,vbias,reset
  
   Reg_data[0]=0x05;
    ADS126xWriteRegister(0x02,1,Reg_data);   //Interface REG    status,  CRC checksum  disable,  4data/6data
  
   Reg_data[0]=0x00;
    ADS126xWriteRegister(0x03,1,Reg_data);   //Mode0 REG runmode , chop , delay
  
   Reg_data[0]=0x80;   //取消电流源
  //Reg_data[0]=0x96;  //10M电阻
   ADS126xWriteRegister(0x04,1,Reg_data);   //Mode1 REG Bias ADC Connection,Sensor Bias Polarity,sensor bias current
  

    Reg_data[0]=0x89;   //DISable PGA  Data Rate 1200sps
    ADS126xWriteRegister(0x05,1,Reg_data);   //Mode2 REG PGA Bypass Mode,  Gain, Data Rate 1200sps
  
   //Reg_data[0]=0x01; // AIN0+, AIN1-
     Reg_data[0]=0x23; // AIN2+, AIN3-   //TEMP
    // Reg_data[0]=0x21; // AIN2+, AINCOM-   //TEMP
   //Reg_data[0]=0x45; // AIN4+, AIN5-   //FLOW
   //Reg_data[0]=0x67; // AIN6+, AIN7-   //PMT   
   //Reg_data[0]=0xee;   //TDACP  TDACN  选择输入端
   //Reg_data[0]=0xbb; //测温
      ADS126xWriteRegister(0x06,1,Reg_data);   //Input Multiplexer REG Positive Input, Negative Input Multiplexer AIN0+, AIN1-
  

   
   Reg_data[0]=0xbb;  //不连接
    ADS126xWriteRegister(0x0d,1,Reg_data);   //IDAC Multiplexer REG IDAC2,IDAC1 Output Multiplexer  No Connection

     Reg_data[0]=0x00;  //OFF
     ADS126xWriteRegister(0x0e,1,Reg_data);   //IDAC Multiplexer REG Selects the current values of IDAC1 /IDAC2  OFF
   
   //Reg_data[0]=0x00;  //内部参考2.5V
   Reg_data[0]=0x11;  //外部参考2.5V
    ADS126xWriteRegister(0x0f,1,Reg_data);   //Reference Multiplexer REG Reference Positive/Negative Input 内部2.5V
   

   Reg_data[0]=0x13; //page54  positive  2.4688v
    ADS126xWriteRegister(0x10,1,Reg_data);   //TDAC  DACP=1.5V    page54

   Reg_data[0]=0x14; //page54  negative  2.4375v  
    ADS126xWriteRegister(0x11,1,Reg_data);   //TDAC   DACN=0.5V   page54
   
   //ADC2

   Reg_data[0]=0x48;   //1V/V  bypass  external 2.5V
   ADS126xWriteRegister(0x15,1,Reg_data);   //ADC2 Configuration REG ADC2 Data Rate /Reference Input /Gain   100SPS  2.5V  1V/V
   
   //ADC2
   //Reg_data[0]=0x23;  //AIN2+, AIN3-
   Reg_data[0]=0xbb;  //测温
    ADS126xWriteRegister(0x16,1,Reg_data);   //ADC2 Input Multiplexer REG Selects the ADC2 positive/Negative  input  AIN2+, AIN3-

   ADS126xSendStartCommand(); 
   ADS126xSendADC2StartCommand();
 
}

Thanks and best regards,

Star

My phone number: +86  189-168-356-25

Hi Star,

Thanks for the additional details.

user4733497 said:

1.   Yes, the(ADC1) AIN2 channel sampling value is always full-scale when external reference input is 2.5 V.

2.   When using internal reference voltage, (ADC1)AIN2 channel sampling is normal.

This would make it seem like there might be an issue with the external reference voltage...

user4733497 said:

   Reg_data[0]=0x11;  //外部参考2.5V
    ADS126xWriteRegister(0x0f,1,Reg_data);   //Reference Multiplexer REG Reference Positive/Negative Input 内部2.5V

This might be the problem... Programming the REFMUX register to "0x11" selects AIN2/AIN1 pins as the external reference source. This should be changed to "0x09" to select the AIN0/AIN1 pins.

For the ADC2CFG register, use "0x08" to select AIN0/AIN1 for the reference source to ADC2.

Try the above change and let me know if that resolves your issue!

If you still have problems after making that change, then I would ask/suggest the following...

• What is your external reference source, and would you be able to share a schematic of it?
• You might want to try measuring the AIN0/1 voltage using the internal reference to check what voltage the ADC is seeing on these pins.

Thanks and best regards,
Chris

Chris，

1.Configuration is as follows：

void  write_ADS126xREG(void)      
{      
   ADS126xSendStopCommand();
   ADS126xSendADC2StopCommand();
   ADS126xSendResetCommand();    //复位、校准
    
    Reg_data[0]=0x03;//使能内部参考,取消内部电平输出
    ADS126xWriteRegister(0x01,1,Reg_data);   //power REG ref,vbias,reset
  
   Reg_data[0]=0x05;
    ADS126xWriteRegister(0x02,1,Reg_data);   //Interface REG    status,  CRC checksum  disable,  4data/6data
  
   Reg_data[0]=0x00;
    ADS126xWriteRegister(0x03,1,Reg_data);   //Mode0 REG runmode , chop , delay
  
   Reg_data[0]=0x80;   //取消电流源
    ADS126xWriteRegister(0x04,1,Reg_data);   //Mode1 REG Bias ADC Connection,Sensor Bias Polarity,sensor bias current
  
//   Reg_data[0]=0x09; //enable PGA  1v/v
//   Reg_data[0]=0x19; //enable PGA  2v/v
//   Reg_data[0]=0x29; //enable PGA  4v/v
//   Reg_data[0]=0x39; //enable PGA  8v/v
//   Reg_data[0]=0x49; //enable PGA  16v/v
//   Reg_data[0]=0x59; //enable PGA  32v/v

   Reg_data[0]=0x89;   //DISable PGA  Data Rate 1200sps
   ADS126xWriteRegister(0x05,1,Reg_data);   //Mode2 REG PGA Bypass Mode,  Gain, Data Rate 1200sps
  
   //Reg_data[0]=0x01; // AIN0+, AIN1-
     Reg_data[0]=0x23; // AIN2+, AIN3-   //TEMP

      ADS126xWriteRegister(0x06,1,Reg_data);   //Input Multiplexer REG Positive Input, Negative Input Multiplexer AIN0+, AIN1-
   
   Reg_data[0]=0xbb;  //不连接
    ADS126xWriteRegister(0x0d,1,Reg_data);   //IDAC Multiplexer REG IDAC2,IDAC1 Output Multiplexer  No Connection

     Reg_data[0]=0x00;  //OFF
      ADS126xWriteRegister(0x0e,1,Reg_data);   //IDAC Multiplexer REG Selects the current values of IDAC1 /IDAC2  OFF
   
   Reg_data[0]=0x00;  //内部参考2.5V  
   //Reg_data[0]=0x09;  //外部参考2.5V
   
    ADS126xWriteRegister(0x0f,1,Reg_data);   //Reference Multiplexer REG Reference Positive/Negative Input 内部2.5V
   

   Reg_data[0]=0x13; //page54  positive  2.4688v
   ADS126xWriteRegister(0x10,1,Reg_data);   //TDAC  DACP=1.5V    page54
   

   Reg_data[0]=0x14; //page54  negative  2.4375v
    ADS126xWriteRegister(0x11,1,Reg_data);   //TDAC   DACN=0.5V   page54
   
   //ADC2
  
   Reg_data[0]=0x48;   //1V/V  bypass  external 2.5V
   ADS126xWriteRegister(0x15,1,Reg_data);   //ADC2 Configuration REG ADC2 Data Rate /Reference Input /Gain   100SPS  2.5V  1V/V
   
   //ADC2
   //Reg_data[0]=0x23;  //AIN2+, AIN3-
   Reg_data[0]=0xbb;  //测温
    ADS126xWriteRegister(0x16,1,Reg_data);   //ADC2 Input Multiplexer REG Selects the ADC2 positive/Negative  input  AIN2+, AIN3-

   ADS126xSendStartCommand();
   
     ADS126xSendADC2StartCommand();
 
}

 2.input signal source：

 

3. this voltage is ratiometric to external reference source.

Other configurations are the same，Only change the reference voltage：

  //Reg_data[0]=0x00;  //内部参考2.5V  
   Reg_data[0]=0x09;  //外部参考2.5V
    ADS126xWriteRegister(0x0f,1,Reg_data);   //Reference Multiplexer REG Reference 

 

 

 

4. schematic :  AVDD= 2.5V, AVSS= -2.5V, DVDD= 3.3V; REF2V5= 2.5V;

 

 

5. Looking forward to your reply.

 

 

 

 

 

 

Hi,

From looking at the schematic I noticed that the capacitor on the REFOUT pin is missing... The ADS1262 datasheet suggests the use of a 1uF cap on this pin. Without a capacitor on REFOUT it is possible for the internal reference to oscillate and cause the gain error you are seeing.

Since your input signal is not coming for a low-output impedance source, but from a resistor divider, I would also highly recommend using the PGA (enabling it) to avoid additional gain errors as a result of the lower input impedance of the delta-sigma modulator when the PGA is bypassed.

I would try adding a capacitor to the REFOUT pin to check if this resolves your issues with the internal reference; however, you probably want to stick with the external reference when measuring the NTC thermistor as it will provide a more ratiometric measurement.

Best regards,
Chris

Chris，

  Plus the capacitance problem solved.

  Thank you very much for your reply.