This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AFE4403 Green, Red and IR LEDs in the common anode configuration with swtiching TX3_MODE

Other Parts Discussed in Thread: AFE4403EVM, AFE4403

Hello,

As subject, once TX3_MODE is set at 1, then TX3_MODE keeps active all the time even though it is set back at 0, according to my test. Or should any settings of registers be set in advance before setting TX3_MODE = 0, like setting CONTROL1 TIMEREN = 0?

Please help comment the solution. Thanks.

  • Hello Ming,

    TX3_MODE can be independently controlled in write mode.

    Do you see this on the afe4403EVM  or in your development board?

    Can you  check if you put the device  back to write  mode  before setting the TX3_MODE = 0?

    Regards

    Praveen.

  • Hi Praveen,

    It is in write mode before setting TX3_MODE=0; to make sure of this, the CONTROL3 register 0x31 (49) value is read as 0x000008 (CLKOUT_TRI = 1b due to not used) dumped to PC via UART.

    The AFE4403 I got in May was engineering samples and designed in our development board, and except switching TX3_MODE, others look OK so far. Please help check why.

    Thanks.

    Ming

  • Hello Ming,

    If I understand correctly, you are able to read and write to all the bits in the AFE registers except TX3_MODE bit.

    For the TX3_MODE bit, you are able to write a '1' to it but unable to set to '0'.

    We have not come across this issue before.

    Provide your register settings so that we will try to replicate this at our end.

    Also provide a procedure that you follow to configure the TX3_MODE bit.

    Do you know who your local TI support is? How did you get the engineering samples?

      

    Regards

    Praveen.

  • Hi Praveen,

    Now, setting TX3_MODE bit at 1 or 0 can get the correct response, but a new issue is met as No. 3 as follows; here is the ADC data that LEDs are put to face a brown color desk:

    1. If TX3_MODE = 1 all the time with LED-On 100us and PRF 125HZ, register 42 (Green) and 44 (Red) values are stable around 0x010997 and 0x0718B2 respectively (variation at D11~D0).

    2. If TX3_MODE = 0 all the time with LED-On 100us and PRF 125HZ, register 42 (IR) and 44 (Red) values are stable around 0x0883EA and 0x0718CD respectively (variation at D11~D0).

    3. If TX3_MODE = 1 for 20 cycles and then 0 for 20 cycles with LED-On 100us and PRF 125HZ, register 44 (Red) value is still stable whenever TX3_MODE=1 or 0, but register 42 (Green/IR) values are not stable to vary 0x089458~0x011999 when TX3_MODE=1  and 0x02C721~0x088A07 when TX3_MODE=0. The variation of register 42 is not just for the first some cycles after changing TX3_MODE, which means each cycle data is different. However, if LED-On is changed to 500us, the ADC value becomes stable except the first 5 cycles after changing TX3_MODE.

    According to spec, a typical time delay of approximately 20ms is required for the receive channel to settle after a change to the TX3_MODE setting, and how should any registers be changed during the 20ms?

    The local contact window is AVNET in Taiwan, and I got the engineering samples from them, but their FAE is not familiar with AFE44xx series.

    Thanks.

    Best regards,

    Ming

  • Hi Ming,

     

    I evaluated a condition which you meant. However I couldn't see the behavior. It was stable. As far as I saw, the maximum variation was 0.008%(3312bit / 2^ 22bit) under following condition. Please see captures below.

     

    - The mode is switched per 20 PRF cycles.

    - LED current : 5mA

    - PRF : 125Hz

    - LED-On : 100us (Duty cycle : 6.25%)

    - Filter : 500Hz

    - R_f : 100 kOhms

     

    Note : it took 30ms to 40ms for settling the LED current after the mode transition.

     

    5773.ADC_code_20140723a.xlsx

    Could you provide us more detail? We would like to get detailed setting and captures.

    Please let me know if you have any questions.

     

    Regards,

     

    Takashi Onawa

  • Hi Takashi, 

    The settings in our development board are:

    The timing sequence of register 1 to 29 follows the way on page 33 of the AFE4403 sepc, but with different pulse On duration of 100, 200 and 500us.

    LED current of Green, Red and IR: 5mA

    PRF: 125Hz

    LED-On: 100us, 200us, and 500us

    NUMAV: 0

    Rf: 100K

    Cf: 5pF

    Please refer to the attached log data, and you can see the values with LED-On 100, 200 and 500us have some variation. 

    How to set Cf to get filter 500Hz? Thanks.

    0181.teraterm_LED5mA_RF100K_CF5pF_NUMAV0-20140724b.xlsx

    Best regards,

    Ming

  • Hi Ming,


    The settling time is dependent on a low-pass filter which is indicated on following figure.

    It needs more than 20ms if low Duty cycle such as 1.25% is applied. This is because a capacitor in the filter needs much time to charge itself first. So if you would like to use a low Duty cycle, you should wait more for the switching time. Please see the following graph which indicates Duty cycle vs settling time.

    We got a similar data to above graph in our evaluation. As a result, you need to wait more than 20 cycles to settle the detected current if you would like to use short LED-ON time. So we would like you to use 50 cycle or more for the TX3 switching on your condition.

    Please let me know if you have any questions.

    Regards,

    Takashi Onawa 

  • Hi Takashi,

    After testing with LED-On 500us and 48ms settling time for PRF 125Hz, the ADC data looks OK.

    #1. However, to set NUMAV at 0, 8 and 9 (for 500us, the maximum of NUMAV is 9), ADC data variation with NUMAV 0 is more stable; could you help check why?

    #2. If Stage2 Gain is enabled, how much noise level will be introduced, 3dB or else? Increasing LED current is a better way, I think, but it will increase power consumption; could you also comment that?

    Thanks.

    Ming

  • Hello Ming,

    We will have to make few measurements to look at the variation of ADC data with the number of averages for your settings. I am checking with my systems team for your second question.

    We will get back to you as soon as possible.

     

    Regards

    Praveen.

  • Hello Ming,

    #1.

    I measured RMS and P-P noise with your condition. But I didn't see the unstable phenomenon. Both noise tended to be decreased with the increasing number of NUMAV value.

    Could you tell us detailed conditions and provide us experimental results?

    These noise are influenced a great deal by environmental variation such as a shake or ambient light variation. We would like to confirm whether the issue was caused by the environmental variation or not.

    #2.

    Stage 2 gain will improve the SNR a bit – maybe 4-5 dB.

    You would use Stage 2 gain either if your signal at the TIA output is very small even with the highest TIA gain setting (or if you can subtract a DC level using the ambient DAC in order to be able to gain up the residual signal without saturating the ADC).

    The other way to increase the signal at the ADC input of course is to use a larger LED current setting but that would increase power consumption. One way to get around it would be to use shorter LED pulses – say as low as 50 or 100 us. To short a pulsewidth would cause amplification of both the sensor noise as well as the TIA noise.

    Regards,

    Takashi Onawa