TPS65185: E-ink - Power down fading

Part Number: TPS65185

Hello,

We are using a TPS65185 with a E-ink screen on a custom board and we are experiencing some issues with repetitive partial-refreshes. The black and the white are getting grey at each partial refresh.

Click here to play this video

We discovered that the fading occurs at the power-down of the TPS65185. We are partially refreshing the screen at least every seconds and currently, the active discharge is not implemented on our board. The discharge of the rail seems to be too slow for the refresh frequency (especially VCOM).

Is it a known issue, and can the active discharge fix it?

What power consumption increase should we expect by implementing the active discharge?

Since we are refreshing the screen every second, is it worth it to turn off the TPS65185, or should we just keep it active as long as we refreshing the screen often?

Best,

Vincent LINTILHAC

  • Here some capture of the issues.

    - Fading of the black:

    - Grainy image:

  • Here the schematic for this project

  • Hi Vincent,

    This is a legacy device, so unfortunately I cannot comment whether this is a known issue, but I can assist with your troubleshooting.

    The power consumption by the active discharge circuits will be much smaller than the device operating currents.

    I will need some additional info before I can address your other questions:

    1. Is it possible to connect an external pull-down resistor to speed up the discharge and confirm if the active discharge can resolve the issue?
    2. Could you explain how you 'turn off' the PMIC during the refresh? Are you removing power, entering the SLEEP state, or something else?
    3. Could you please attach a higher resolution file of the schematic?

    Thanks,

    Gerard

  • Hi Gerard,

    1) We cannot connect an external pull-down resistor to try out the active discharge.

    2) After the refresh, POWRUP is pulled down, so the device is going from ACTIVE to STANDBY mode

    3) Please note the  R50 is not implemented on our board

    Let me know if you need anything else

  • Thank you Vincent. I will be having a look at this while Gerard is out of office. I should be able to get back to you on this by Wednesday. Thank you.

    Regards,

    Alex

  • Hi Vincent,

    Since you are unable to implement the active discharge, is it possible to lower the frequency of the refresh to allow for more time to discharge the rails?

    Regards,

    Alex

  • Hi Alex,

    Thanks for the answer, I'll try to reduce the refresh frequency, to see if this has an impact on the screen fading, and I'll let you know.

    I also have a question about Gerard comment about this product being a legacy device. What does he meant by that? The device is marked as ACTIVE on your website, is there a EOL notice that I missed and a replacement compatible if that's the case?

    Best,

    Vincent

  • Vincent,

    I will ask Gerard what he meant by that when he returns next week. I also see it active and am unaware of a replacement part myself but Gerard has more experience with this portfolio an likely knows something I do not.

    Regards,

    Alex

  • Hi Alex,

    I tried to reduce the refresh frequency but it doesn't have any effect on the problem. The fading occurs when the rails are discharging and not when the rails are brought back up.

    If I never discharge the rails, the problem is not occurring, but the power consumption is increase which is not the best option.

    Best,

    Vincent

  • Hi Alex,

    In that case it would be best to confirm if a faster discharge process eliminates the fading. Is there no way to add an external discharge resistor in parallel with the VCOM (and any other) output capacitors on your PCB?

    Unfortunately the schematic is still not readable for me. Do you have a PDF version or something downloadable? 

    Thanks,

    Gerard