Use of NVCC_LCD

[AndrewS_]

Hey,

I was unable to find much regarding use of i.MX53 NVCC_LCD in datasheet/User's Guide/Quick Start Reference Manual or Forums. I was wondering, if I am not planning to use an LCD panel nor the DISP0_DAT[0..23] GPIOs, but I am going to use the TVE/LDB, is it safe to tie the NVCC_LCD to ground? Or it should be left floating is such case?

My concerns are: saving power and component space.

[JorgeRama_rezRi]

Hi Mark,

I wasn't aware about this new info. Thanks for sharing it!

Best regards.

Jorge.

[TheAdmiral · Accepted solution]

Do not connect NVCC_LCD to ground. The i.MX53 Processor was not designed to run in this condition. In all ICs, there are internal leakages. Think of the IC like the SR-1 Spy plane. It leaks fuel on the tarmac, but the gaskets seal in flight at designed operating altitudes. The processor was designed to run with all modules powered for best performance, or for standby condition, core voltages applied, and module voltages turned off (but not connected to ground).

The recommendation is to tie NVCC_LCD to a voltage rail even if it is not being used. 1.8V or 2.775V is recommended by the datasheet, if available. The good news is that coupling capacitors would not be required in this case, so you are saving on components. Power savings can be maximized by disabling the pull ups/keepers for each pin. If you float NVCC_LCD, you will still get some power loss through this module from surrounding modules.

This is information from the chip team that just came up in the last week Jorge. I'm not trying to make you look bad. :) My first guess would have been floating would be all right.

[paulmichalczuk]

Hi Mark,

I was wondering if you were able to share any insight on using the TVDAC_COMP and TVDAC_VREF pins if I do not plan on using the the TVE functions (just GPIO). I apologize if this is in the manual/PDFs.

Thank You,

Paul

[Paul1z]

If we are using the NVCC_LCD pins as GPIO (1.8V), do I need to have a cap on the TVDAC_COMP pin and a resistor on the TVDAC_VREF pin? You mentioned that decoupling caps would not be needed - would we still need an inductor in series (we are using an inductor in series from the power supply with 2x bypass caps going to the TVDAC_AHVDDRGB_1, TVDAC_AHVDDRGB_2, and TVDAC_DHVDD pins).

[JorgeRama_rezRi]

Hi A.S,

If none of the pins that are supplied by NVCC_LCD are being used, then NVCC_LCD can be left floated. Please take into account the following note in the datasheet:

- All IO pins should not be externally driven while the IO power supply for the pin (NVCC_xxx) is off. This can cause internal latch-up and malfunctions due to reverse current flows.

Also, please take into account that even if you are not using the LCD panel, the LCD pins are muxed with signals of other blocks, so you may want to use these pins for another purpose. If you are sure you won't use any of these pins, then you can leave NVCC_LCD floated.

Best regards.

Jorge.