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TPS65186 VCOM fault

Andrew Felch
Prodigy 20 points
Other Parts Discussed in Thread: TPS65186

Hello,

I am trying to power up the TPS65186 epaper power chip but any time I try to power up the rails I get a VCOM fault (INT2 register has bit 2, the 3rd bit, set).  I measure voltage on VCOM and it is around 0.5v, which is within the range of -5v to 1v described by the datasheet as OK.  

Do I have to run a VCOM setup routine?  Is there some way to get this chip to power up?  Is there a known good startup routine?  We have VCOM tied to both VBORDER and VCOM of the screen, and have tried it with the screen plugged in and without.

-Andrew

  • 0
    Prodigy 20 points

    If I set VCOM to HiZ (set bit 5, sixth bit, of VCOM2 to 1) prior to setting PWR_UP to 1, then i get a PWR_UP = 250, i.e. success - but when I have a screen plugged in it gives me the same VCOM2 fault error.  I tied VCOM output with a strong pull (470 ohm) to ground and, with screen plugged in, get a new error: INT2 has bit 5, sixth bit, set indicating "VN_UV", "Inverting buck-boost converter under voltage detected - under voltage on DCD2 detected".  Did I get further in the process to powering up the screen, or less far?  (i.e. did the pull to ground help?)

  • 0 in reply to Andrew Felch
    TI__Genius 10885 points

    Hi Andrew,

    Since DCDC2 is likely the source for VCOM_PWR, this strong pull-down may be just introducing an additional fault condition on DCDC2. The VCOM fault seems defined by the -5.5 to 1V range, so possibly VCOM is rising the addtional 500mV from your measured value.

    Have you tried the VCOM adjustment mentioned in section 8.3.6 and 8.3.6.1 of the datasheet?