In the recent project I am working on I want to connect a TFT LCD to ESP32-S3. I would be using the LCD hardware interface of ESP32, so I only need to take proper care of display power management. The model I have currently, is ZJ050NA-08C by Innolux.
I have already figured out the way of generating all the needed voltages (DVDD, AVDD, VGH, VGL, VCOM) using boost converters and charge pumps (quite a common topology). But I have some doubts regarding the needed power-up and power-down sequence.
So first, the official datasheet mentions the following sentence:
Be sure to apply GND, DVDD and VGL to the LCD first, and then apply VGH
This gives me a hint already, about the correct sequence of events at start-up. There is also a timing diagram provided though:
Here we can see that after applying VDD (and I am assuming it's DVDD here, right?) I should apply AVDD asap, and introduce some small delay for VGL and VGH lines. This should be easy enough with some transistors and RC-based delay circuits on the VGL and VGH lines. What really is a mystery for me is a shut-down sequence:
Can you guys please help me understand that sequence? I have a few questions:
- I can see that I should keep the VGH and VGL lines for at least 20ms after the backlight turns off. This should be quite easy with some RC circuits again, as both VGL and VGH are said to consume only as little as 0.2mA of current. But do you happen to know where might that requirement come from?
- The sequence shows the AVDD and VCOM lines to go down after the VGH/VGL but without giving any specific timings. Does that mean I can turn these off whenever I want, as long as it's after VGH and VGL? This might be a bit tricky as AVDD line is said to consume around 10mA or current, so keeping it active might be a bit harder. Do you have any ideas how I can achieve this?
- We can see that I should release the data lines and shut down DVDD line at least 50+ms after VGH/VGL. That seems doable as long as I still have power supplied for the whole board. What if it's not a soft shut-down, triggered by the ESP but it's a result of cutting off the power for the whole board? For example if I unplug the power supply cable. I can maintain some power for the VGH and VGL lines, but doing this for AVDD and DVDD lines, which both can consume lots of current is not really doable for 50+ms (unless I have some battery). So how should I handle this case? Should I just ignore the 'full power loss' scenario, as it's generally a problem for the LCDs and I can't do anything about this?
