RGB LCD Ghosting/Burn-in After Backlight Timeout - ST7262 Controller (Waveshare ESP32-S3-Touch-LCD-5B)

[ReacherS3]

RGB LCD Screen Ghosting/Burn-in Issue

Hardware Configuration

• Board: Waveshare ESP32-S3-Touch-LCD-5B
• MCU: ESP32-S3
• LCD: 1024x600 RGB LCD with ST7262 timing controller
• Interface: 16-bit RGB565, 21MHz pixel clock
• Backlight: Switch-type via CH422G IO expander (pin 2)
• ESP-IDF: v5.4.3
• Library: ESP_Panel_Library (ESP Display Panel)

Problem Description

When implementing a backlight timeout feature (turn off backlight after 30 seconds of inactivity), the LCD exhibits significant ghosting/burn-in effects. After the backlight turns off and remains off for 5+ minutes, a faint "ghost" image of the last displayed content persists on the screen even after the backlight turns back on.

Attempts to Resolve

1. Display Control Commands

Attempted: Using lcd->setDisplayOnOff(false) to send DISPOFF command
Result: Error - "function not supported"
Reason: ST7262 is an RGB timing controller, not a command-based LCD controller. It has no command interface.

2. Software Black Overlay

Attempted: Created full-screen black LVGL object before turning off backlight

black_overlay = lv_obj_create(lv_scr_act());
lv_obj_set_style_bg_color(black_overlay, lv_color_black(), 0);
lv_refr_now(NULL);
vTaskDelay(pdMS_TO_TICKS(100));
backlight->off();

Result: Ghosting still occurs after 5+ minutes
Reason: RGB LCD continuously receives data from ESP32 RGB peripheral regardless of content

3. Hardware LCD Reset

Attempted: Pulling LCD_RST low via CH422G IO expander (pin 3) before turning off backlight

expander->digitalWrite(LCD_RST_EXPANDER_PIN, 0);  // Pull reset low
vTaskDelay(pdMS_TO_TICKS(5000));
backlight->off();

Result: No effect - ghosting persists
Reason: LCD_RST may not actually cut power to the panel, or reset doesn't affect the liquid crystal state

4. Enhanced Rendering with Delays

Attempted: Multiple render cycles with delays

lv_obj_move_to_foreground(black_overlay);
lv_refr_now(NULL);
vTaskDelay(pdMS_TO_TICKS(150));

Result: No improvement

Technical Analysis

RGB LCD Architecture

• ST7262: RGB timing controller that passes through RGB data from ESP32
• No frame buffer: Unlike SPI LCDs, RGB LCDs have no internal GRAM
• Continuous refresh: ESP32 RGB peripheral continuously sends pixel data
• No power management: ST7262 has no built-in display enable/disable capability

Board Configuration

// From BOARD_WAVESHARE_ESP32_S3_TOUCH_LCD_5_B.h
#define BOARD_LCD_RGB_IO_DISP                   (-1)  // No display enable pin available
#define BOARD_IO_EXPANDER_OUTPUT_IO_0_PINS      {2, 3, 1}  // Backlight, LCD_RST, Touch_RST

Root Cause

The ghosting appears to be an inherent physical characteristic of the LCD panel's liquid crystals. Some lower-cost RGB TFT panels have slower liquid crystal response times and retain a faint image even when:

1. Displaying solid black
2. Backlight is off
3. No power signal changes occur

Questions for Espressif

1. RGB Peripheral Control: Is there an API to pause/stop the ESP32-S3 RGB peripheral (stop PCLK, disable DE signal) while keeping the LCD initialized?

2. Panel Blanking: Does ESP-IDF provide any low-level functions to "blank" an RGB panel without destroying the driver instance?

3. Hardware Recommendations: For RGB LCDs that need power management, what is the recommended hardware approach? Should we:

   • Add external circuitry to cut VDD to the LCD panel?
   • Use a different LCD type (MIPI DSI, SPI) for applications requiring display off?
   • Accept this as normal behavior for RGB LCD panels?

4. Best Practices: What is Espressif's recommended approach for implementing screen timeout on RGB LCD panels to minimize ghosting/burn-in?

Current Workaround

Currently using simple backlight on/off with acceptance that some ghosting may occur as a hardware limitation of the LCD panel.

Request

Looking for guidance on whether:

• This is expected behavior for RGB LCD panels
• There are undocumented APIs or techniques to mitigate this
• Hardware modifications are necessary
• Different display technology should be used for this use case

Any insights would be greatly appreciated!