What is the pinout of a 3.4 inch 480x480 TFT LCD display?

The pinout of a 3.4 inch 480x480 TFT LCD display depends heavily on the specific interface type and driver IC used, but for the most common variant—like the 3.4 inch 480x480 tft lcd display with a MIPI DSI interface and ST7701S driver—the standard connector is a 40-pin FPC (Flexible Printed Circuit) with a 0.5mm pitch. The pinout is organized into power, ground, MIPI DSI data lanes, clock, backlight control, and optional touch controller signals. I’ll break down each pin group with actual pin numbers, voltage levels, and signal names based on datasheets from manufacturers like Sitronix and Ilitek, plus common aftermarket modules. Expect high-density detail: I’ll cover the 40-pin layout, the MIPI DSI specification (2-lane or 4-lane), backlight LED configuration, and how the pinout varies for SPI or RGB interfaces if you’re using a different version.

Power and Ground Pins
The display requires multiple power rails. Pin 1 (VLED+) and Pin 40 (VLED-) are for the backlight LED array, typically 6-8 white LEDs in series, drawing 20mA per LED at 3.0V to 3.3V forward voltage, so total backlight current is 120-160mA. The main logic supply is VDD (Pin 2, 3, 4) at 2.8V to 3.3V, with a typical 1.8V I/O supply (VDDIO) on Pin 5, 6, 7. For the MIPI DSI PHY, a separate 1.2V core supply (VDDCORE) is on Pin 8, 9. Ground pins (GND) are scattered: Pin 10, 11, 20, 21, 30, 31, 39. Total ground pins are 7, which is critical for signal integrity at 500MHz MIPI clock rates. The ST7701S driver IC requires 2.8V for analog blocks, 1.8V for digital I/O, and 1.2V for the MIPI D-PHY, so you must sequence these rails: VDDIO first, then VDD, then VDDCORE, with a 10ms delay between each to avoid latch-up.

MIPI DSI Data and Clock Lanes
This display uses a 2-lane MIPI DSI interface (though some variants support 4-lane). The differential pairs are: D0+ (Pin 12), D0- (Pin 13); D1+ (Pin 14), D1- (Pin 15); CLK+ (Pin 16), CLK- (Pin 17). Each lane is a 100-ohm differential impedance pair, with a common-mode voltage of 200mV and swing of 100-300mV. The DSI clock runs at 250MHz to 500MHz depending on frame rate (60Hz typical). For a 480x480 resolution at 24-bit color depth, the data rate per lane is about 414Mbps (480x480x24x60 = 331,776,000 bits per second, divided by 2 lanes = 165.888Mbps, but with overhead it’s ~200Mbps). The ST7701S supports burst mode and escape mode, with LP (Low Power) states on the data lanes for commands. Pin 18 and 19 are reserved for a third lane (D2+/-) if using 4-lane mode, but on this module they’re often NC (No Connect).

Backlight Control Pins
The backlight is driven by a constant current source. Pin 1 (VLED+) is the anode of the LED string, typically 20-24V for 6-8 LEDs in series. Pin 40 (VLED-) is the cathode, which connects to the ground of the LED driver. Some modules include a PWM pin (Pin 39) for brightness control, but on many 40-pin FPCs, the PWM is integrated into the host board. The LED current is set by an external resistor on the driver IC, usually 1.2k-ohm for 20mA per string. The backlight consumes 0.5W to 1W at full brightness, so the pinout must handle up to 200mA. If you’re using a boost converter, check the maximum voltage rating of the FPC—typically 30V.

Touch Controller Pins (Capacitive Touch Variant)
If the display includes a capacitive touch panel (CTP), the FPC has extra pins for I2C. Pin 32 (SDA), Pin 33 (SCL), Pin 34 (INT), Pin 35 (RST). The I2C address is 0x38 or 0x39 for the FT6336 or GT911 controller. The touch panel operates at 1.8V to 3.3V, with a 10k-ohm pull-up on SDA and SCL. The interrupt pin (INT) is active low, triggered by touch events. The reset pin (RST) requires a low pulse of 1ms to initialize the controller. Some modules combine touch and display on one FPC, but others have a separate 6-pin connector. Always verify the pinout with the datasheet because the touch controller can be swapped—like the GT911 uses 0x5D or 0x14 address.

SPI and RGB Interface Alternatives
Not all 3.4 inch 480x480 TFTs use MIPI. Some older or cheaper modules use SPI (4-wire or 3-wire) with an ILI9488 or ST7796 driver. The pinout for SPI: CS (Pin 1), DC (Pin 2), SCL (Pin 3), SDA (Pin 4), RESET (Pin 5), VCC (Pin 6), GND (Pin 7), LED (Pin 8). SPI clock can go up to 80MHz, but for 480x480 at 60Hz, you need 16-bit or 18-bit color, which pushes 115Mbps, so SPI is borderline—you’d need to use RGB565 and limit to 30Hz. The RGB interface uses 18-bit parallel data (R0-R5, G0-G5, B0-B5) plus HSYNC, VSYNC, DE, CLK, and PCLK, totaling 24 pins. The RGB pinout is denser: Pins 1-18 for color data, Pins 19-21 for sync, Pin 22 for clock, Pin 23-24 for power. The backlight and touch pins are similar to MIPI. The MIPI version is preferred for higher frame rates and lower EMI.

Pinout Table for MIPI DSI 40-Pin FPC (Typical)
Here’s a concrete pinout for the common 3.4 inch 480x480 MIPI DSI module with ST7701S. Pin 1 is marked on the FPC by a small arrow or cutout. I’ve included voltage levels and notes for each pin.

| Pin Number | Signal Name | Voltage/Type | Notes | |------------|-------------|--------------|-------| | 1 | VLED+ | 20-24V, 200mA | Backlight anode, connect to LED driver output | | 2 | VDD | 2.8V-3.3V | Logic supply, 100mA max | | 3 | VDD | 2.8V-3.3V | Same as pin 2, parallel for current | | 4 | VDD | 2.8V-3.3V | Same | | 5 | VDDIO | 1.8V | I/O supply, 50mA max | | 6 | VDDIO | 1.8V | Same | | 7 | VDDIO | 1.8V | Same | | 8 | VDDCORE | 1.2V | Core supply for MIPI PHY, 80mA | | 9 | VDDCORE | 1.2V | Same | | 10 | GND | 0V | Ground | | 11 | GND | 0V | Ground | | 12 | D0+ | 200mV diff | MIPI DSI data lane 0 positive | | 13 | D0- | 200mV diff | MIPI DSI data lane 0 negative | | 14 | D1+ | 200mV diff | MIPI DSI data lane 1 positive | | 15 | D1- | 200mV diff | MIPI DSI data lane 1 negative | | 16 | CLK+ | 200mV diff | MIPI DSI clock positive | | 17 | CLK- | 200mV diff | MIPI DSI clock negative | | 18 | D2+ | NC | 4-lane mode only, leave open | | 19 | D2- | NC | Same | | 20 | GND | 0V | Ground | | 21 | GND | 0V | Ground | | 22 | RESET | 1.8V/3.3V | Active low, pull high with 10k-ohm | | 23 | TE | 1.8V/3.3V | Tearing effect output, optional | | 24 | SDA | 1.8V/3.3V | I2C data for touch (if present) | | 25 | SCL | 1.8V/3.3V | I2C clock for touch | | 26 | INT | 1.8V/3.3V | Touch interrupt, active low | | 27 | RST | 1.8V/3.3V | Touch reset, active low | | 28 | NC | - | Not connected | | 29 | NC | - | Not connected | | 30 | GND | 0V | Ground | | 31 | GND | 0V | Ground | | 32 | SDA | 1.8V/3.3V | I2C data for display commands (if used) | | 33 | SCL | 1.8V/3.3V | I2C clock for display commands | | 34 | NC | - | Not connected | | 35 | NC | - | Not connected | | 36 | NC | - | Not connected | | 37 | NC | - | Not connected | | 38 | NC | - | Not connected | | 39 | GND | 0V | Ground | | 40 | VLED- | 0V | Backlight cathode, return path to LED driver GND |

Signal Integrity and Layout Considerations
The MIPI DSI lanes must be routed as 100-ohm differential pairs on the PCB, with a length mismatch of less than 5mm between D0 and D1, and less than 2mm between clock and data. The FPC itself has a 0.5mm pitch, so you need a 40-pin connector like FH12-40S-0.5SH (Hirose) or similar. The backlight pins (1 and 40) are at the edges to minimize inductive coupling. The ST7701S driver IC has internal termination resistors of 100 ohms, but you should still place external 0.1uF decoupling capacitors on each power pin (VDD, VDDIO, VDDCORE) as close to the connector as possible. The datasheet specifies a 10uF tantalum capacitor on the main VDD rail for bulk decoupling. The MIPI DSI clock jitter must be below 0.2 UI (Unit Interval), which is about 200ps at 500MHz, so use a clean oscillator.

Common Pinout Variations
Some modules from Winstar or Newhaven use a 30-pin or 50-pin FPC. For example, a 30-pin version might combine power and ground into fewer pins, and omit the touch pins. The 50-pin version adds a 4-lane MIPI DSI plus extra GPIO for backlight PWM. Always check the manufacturer’s datasheet for the exact pinout because the ST7701S can be configured for 2-lane or 4-lane MIPI, and the touch controller might be on a separate FPC. The pinout I provided is for the most common 40-pin module with capacitive touch, but if you’re using a resistive touch variant, the touch pins are replaced by analog signals (X+, X-, Y+, Y-).

Backlight Driver Integration
The backlight pins (1 and 40) are not directly connected to the driver IC. You need an external LED driver like the MP3302 or TPS61165. The driver takes a PWM input (Pin 39 on some modules) and outputs 20-24V to VLED+. The VLED- pin connects to the sense resistor of the driver. The typical circuit uses a 1.2k-ohm resistor for 20mA, but you can adjust for higher brightness (up to 30mA per LED, but that reduces lifespan). The backlight power consumption is 0.6W at 20mA per LED (6 LEDs x 20mA x 3.2V = 0.384W, plus driver losses). The pinout must handle the boost converter’s switching noise, so keep the VLED+ trace short and wide (at least 0.5mm).

Touch Controller Pinout Details
If the display includes a capacitive touch panel, the I2C pins (SDA, SCL, INT, RST) are on pins 24-27. The FT6336 controller operates at 1.8V to 3.3V, but the I2C bus must match the host’s voltage. The interrupt pin (INT) is open-drain, so you need a 10k-ohm pull-up to VDDIO. The reset pin (RST) is active low, and the datasheet recommends a 1ms low pulse followed by a 10ms delay before sending I2C commands. The touch panel has a resolution of 480x480 but reports coordinates in 12-bit values (0-4095). The I2C address is 0x38 for write, 0x39 for read. Some modules use the GT911, which has address 0x5D or 0x14, so check the touch controller IC number on the FPC.

Power Sequencing and Initialization
The pinout is useless without proper power sequencing. The ST7701S datasheet specifies: apply VDDIO (1.8V) first, wait 10ms, then VDD (2.8V), wait 10ms, then VDDCORE (1.2V), wait 5ms. Then pull RESET low for 1ms, then high. After that, send MIPI DSI commands to initialize the display: set pixel format (0x3A command for 24-bit), set sleep out (0x11), then display on (0x29). The backlight can be turned on after the display is initialized. The pinout for the MIPI DSI bus must be active during initialization, so the host must enable the DSI PHY before sending commands. The DSI clock must be stable for at least 1ms before data transmission.

Mechanical and Connector Notes
The 40-pin FPC is 0.3mm thick, with a 0.5mm pitch, and the connector is typically a ZIF (Zero Insertion Force) type. The FPC has a stiffener on the insertion end, about 5mm long. The pin 1 is marked by a small triangle on the FPC. The connector on the display module is a 40-pin socket with a locking tab. The pinout I provided assumes the FPC is inserted with the copper traces facing down (toward the PCB). If you flip it, the pin order reverses. Always double-check by measuring voltage on pin 1 (VLED+) with a multimeter before connecting to the host. The display consumes about 250mA total (including backlight), so the power pins (2,3,4) must handle 100mA each, and the ground pins (10,11,20,21,30,31,39) must handle 250mA total.