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ADS1296R outputs only 4 data channels

Martin Viteznik
Prodigy 10 points
Other Parts Discussed in Thread: ADS1296R, ADS1292R

Hi,


I have encountered strange behaviour of ECG AFE ADS1296R. I have found two issues so far:

  1. The IC does not provide correct value in ID Control Register.
  2. The IC provides only 4 channels of output data instead of 6 (Channel #5 reads STATUS again, CH#6 reads the same as CH#1; see figure enclosed).

Ad 1: I use code similar to ADS1292R which works flawlessly in such case. When RREG at address "0x00" is issued (i.e. ID register), the value of "0xC0" is returned (0b 1100 0000) instead of "0xD1" (0b 1101 0001). When reading other registers (e.g. GPIO inputs), all values are read as expected (correct default values, correct state of GPIO inputs if toggled).

Ad 2: Either in RDATAC or single-shot mode, the device outputs STATUS word, then CH1..CH4 words. In the place of data bytes for CH5 and CH6, STATUS word and CH1 data are present, which signalizes cycling through to the end of data and reading the data again from the very start.

Is it possible there could be wrong batch of ADS129R ICs? I haven't found any information about any need to "activate" the other two channels.

Supporting data:

ADS1296R - 13ZFGH9G1, bought recently from Farnell.

Two ICs with the same behaviour.

Soldered by vapour reflow, IBL SLC509.

Xray inspection through GE-Phoenix Nanomex 180T.

ID register and singleshot measurements done through BusPirate, SPI at both 125 and 250 kHz. Same behaviour.

Internal reference, internal oscillator.

RDATAC measurements done with custom MCU firmware, waveforms sniffed using DSO, see screenshot with my remarks.

Setup for the scope image: 250SPS mode. CH#1: square test signal, CH#2 through CH#6: shorted and powered off (CHnSET=0x81).

I appreciate any help. Just for information, ADS1292R works well without any issue...

Thanks, Martin Viteznik, Czech Tech Uni, Faculty of Biomed Eng

  • 0
    TI__Guru 66166 points

    Hello Martin, 

    Thank you for your post and my apologies for the delay.

    Can you confirm that you are meeting the Power-On Reset timing guidelines in the datasheet (page 42)? If tPOR is not satisfied, the One-Time Programmable registers in the device (which are burned at the factory) may not be read correctly. This has generally manifested itself when a 6-channel or 8-channel devices powers-up as a 4-channel device due to an incorrect read of the Device ID. This explains why you only see 4 channels worth of data.

    Once the power supplies are up, a /RESET pulse or SPI command should be issued after 218 tCLKS. This will bring up the device in the correct state.

    Best Regards,