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TLC4545 initialization error

Vladimir Aparin
Expert 2610 points

Other Parts Discussed in Thread: TLC4545

My client have error with TLC4545.

They are trying to init the ADC like described on page 12 http://www.ti.com/lit/ds/symlink/tlc4545.pdf
Oscillograms of SCLK(red) and CS(blue) signals are presented on image below.

But about half of ADC IC's are not initialized after this operation and not working properly - ADC sending wrong data.
After power switching down for 5 seconds for all PCB and powering up again - half of ADC IC's is starting properly.
If time of power down less that 5 seconds - ICs is not starting again.
Initialization of TLC4545 started after ending of transient process in power line (i check it on VDD - just a straight line, here is no pulses or oscillations).
How i can fix it?

  • 0
    TI__Expert 4405 points

    Vladimir,

    I apologize for this delay in responding to your post.

    It does appear as though that the TLC4545 is not reset correctly during power up – possibly because of some digital or analog input being applied before the power supplies are stable.

    A few questions to help me understand the problem better:

    1. It is not clear to me how many devices are present on the board? Are some devices always failing or are the failures random?
    2. If there are a large number of devices present, has it been ensured that the SCLK and CS drivers have the drive strength required?
    3. If a valid RESET cycle is issued and recognized by the device, the SDO output during the following cycle is FF00h. Is this how the customer is determining that the reset is failing?

    In case the problem is a power sequence issue alone (and not a drive strength related which, looking at the oscilloscope plot, looks unlikely) one way to work around the problem is to issue a dummy READ cycle before issuing the RESET cycle after power up. Could you request your customer to try this and see if they are able to reset all devices successfully?

    Thanks.

    Regards,

    Sandeep