CFAG160160B Current draw at power-up

[Tot]

I have been using this display successfully for some time now but have one issue with it.

I am controlling it directly from a PIC micro (EN, CS, RS, RXW direct from 3V3 logic) , with the data lines (DB0-7) going via a level-shifter.

At power-up, when all control lines (3V3) are floating (and level-shifter i/o are hi-z), I find the +5V rail goes into current-limit and drops to around 3V.

Once the code is running the current drops to within the regulator's supply limits and all is fine (although I haven't measured the ACTUAL current).

I cannot see anything in the datasheet regarding initialisation states of the control pins. Am I missing something? Eg, does EN pin have to be low at power application? Is there a defined power-up sequence?

Regards,

Tot

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[CF Tech]

Having CMOS lines floating can be bad.

Maybe put a pull-up (or pull-down, as needed) on the level shifter's enable line so its outputs are driven low (or high, does not really matter) for the time between when the power is applied and the micro gets control.

Another method would be to put a pull-up (or down) on every line going to the LCD.

Please give one of these a try and see if it helps.

 

[Tot]

Thanks for the prompt reply.

Since earlier today I discovered that trimming the contrast pot (in the direction of reduced contrast) resulted in the display not going into the high-current mode.

It only took a slight adjustment to get stability. Any explanation for this?


Further info on the unstable mode: At power-up the voltage rail is always stable 5V. After a few seconds current then ramps up and the rail drops.

Regards,

Tot

 

[Tot]

Looking back through my notes and comparing with my colleague, we have had problems a while ago where the units seemed to die. See my post from 2006/02/03.

It appeared this was related to the negative voltage generator. Do you have a known design issue with this? Could this be part of this issue?

I have tried using pull-downs on the pins (albeit separately one-by-ne) and this doesn't appear to make any difference.

Regards,

Tot