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ADS1194: Can't get lead off status while RL cable

vivek yuvan
Prodigy 190 points
Part Number: ADS1194
Other Parts Discussed in Thread: TINA-TI

Dear Friends

We have a problem with ADS1194, While we remove the RL cable connection we didn't get lead-off status in ECG RAW data

Here below my Reg configuration 

write_ads1298r_reg(W_CONFIG1 , 0X04);		  
		 write_ads1298r_reg(W_CONFIG2 , 0X30);		  
	         write_ads1298r_reg(W_CONFIG3 , 0XDC);     
		 write_ads1298r_reg(W_LOFF ,    0X13);     
     
		 write_ads1298r_reg(W_CH1SET  , 0X50);		  
		 write_ads1298r_reg(W_CH2SET  , 0X50);		  
		 write_ads1298r_reg(W_CH3SET  , 0X50);
		 write_ads1298r_reg(W_CH4SET  , 0X50);
		 write_ads1298r_reg(W_CH5SET  , 0X50);
		 write_ads1298r_reg(W_CH6SET  , 0X50);
		 write_ads1298r_reg(W_CH7SET  , 0X50);
		 write_ads1298r_reg(W_CH8SET  , 0X50);
    
  	  	 write_ads1298r_reg(W_RLD_SENSP  , 0X02);  
	  	 write_ads1298r_reg(W_RLD_SENSN  , 0X06);
		 write_ads1298r_reg(W_LOFF_SENSP  , 0XFF); 
		 write_ads1298r_reg(W_LOFF_SENSN  , 0XFF);  
		 write_ads1298r_reg(W_LOFF_FLIP  , 0X00);


		 write_ads1298r_reg(W_GPIO  , 0X00);
		 write_ads1298r_reg(W_PACE  , 0X00);

		 write_ads1298r_reg(W_CONFIG4 ,0X02); //0x02
		 write_ads1298r_reg(W_WCT1  , 0X0A);
		 write_ads1298r_reg(W_WCT2  , 0XE3);

  • 0
    TI__Guru 66906 points

    Hello Vivek,

    Thank you for your post.

    What is the connection status of the electrode inputs when you remove RLD? Are they connected to something, or to each other? What do the LOFF_STAT bits read in the STATUS word? 

    The RLD amplifier is needed to maintain a mid-supply common-mode voltage at the electrode inputs. When this connection is removed, the common-mode voltage will shift away from mid-supply due to the imbalance of the lead-off current. Currently, you have one positive input selected and two negative inputs selected. This may affect the reported lead-off status for the other inputs, depending on the comparator threshold you have configured. In addition, the output of the PGA may saturate if the voltage at the input becomes large. Currently, you are using a gain of 8 V/V.

    If you can download TINA-TI spice simulator, try modeling your configuration and see how the voltage at each channel input / output is affected.

    DC and AC LOFF - 2CH (ideal).TSC

    Best Regards,