What is the pinout of an HDMI to LVDS adapter?

An HDMI to LVDS adapter converts the digital video signal from an HDMI source into a Low-Voltage Differential Signaling (LVDS) format, which is commonly used to drive flat-panel displays like those in laptops, industrial monitors, and embedded systems. The pinout of such an adapter is not universal; it varies significantly based on the specific chipset, the number of LVDS channels (single or dual), and the target display panel's wiring. However, the core interface typically involves a standard HDMI input connector (Type A, 19-pin) on one side and a multi-pin LVDS output connector (often 20-pin, 30-pin, or 40-pin, depending on the panel) on the other. The HDMI side follows the hdmi to lvds display adapter standard, with pins for TMDS data lanes (channels 0, 1, 2, and clock), +5V power, hot plug detect, and DDC (I²C for EDID). The LVDS side, on the other hand, breaks out into differential pairs for each data lane, along with power, ground, and backlight control signals. Let's dive deep into the specifics, because the devil is in the details when you're trying to wire up a display without a datasheet.

The HDMI input connector on these adapters is almost always a standard 19-pin female HDMI Type A. Pin 1 is the TMDS Data2+ lane, pin 2 is TMDS Data2 Shield, and pin 3 is TMDS Data2-. This pattern repeats for Data1 (pins 4, 5, 6) and Data0 (pins 7, 8, 9). Pin 10 is the TMDS Clock+ lane, pin 11 is the TMDS Clock Shield, and pin 12 is the TMDS Clock-. Pin 13 is the CEC (Consumer Electronics Control) pin, which is rarely used in these adapters. Pin 14 is reserved (often left unconnected), pin 15 is the SCL (DDC clock), and pin 16 is the SDA (DDC data). Pin 17 is the ground for DDC and CEC. Pin 18 is the +5V power supply (typically 50 mA max, but some adapters draw up to 500 mA if the source can provide it). Pin 19 is the Hot Plug Detect (HPD), which signals the source that a display is connected. The shield of the HDMI connector is connected to ground. This is the fixed side; you don't modify it. The adapter's built-in bridge chip, commonly a TFP401, RTD2556, or CH7511, decodes the HDMI stream and converts it into parallel RGB data, then serializes it into LVDS differential pairs.

Now, the LVDS output side is where things get messy. Most adapters use a 30-pin or 40-pin connector (often a JST or Hirose DF13 series) with a 1.0mm or 1.25mm pitch. The pinout is determined by the display panel's specification, but there are common patterns. For a single-channel 6-bit LVDS (18-bit color), you typically have 4 differential data pairs (TX0+, TX0-, TX1+, TX1-, TX2+, TX2-, CLK+, CLK-) plus power and ground. For a single-channel 8-bit (24-bit color), you get 4 data pairs as well, but the mapping includes the extra two bits (LSB) within the existing pairs. For dual-channel 8-bit, you have 8 data pairs (4 per channel) plus a clock pair per channel, totaling 10 differential pairs. That's a lot of pins. Let's break down a typical 30-pin single-channel LVDS connector pinout that many generic HDMI-to-LVDS boards use:

Pin Number	Signal Name	Description
1	VCC (3.3V or 5V)	Power supply for the panel logic, typically 3.3V, but some panels need 5V or 12V. Check the panel datasheet.
2	VCC	Same as pin 1, often doubled for current capacity.
3	GND	Ground return.
4	GND	Ground return.
5	RX0-	LVDS differential pair 0, negative. Carries the first data channel (includes R0, R1, R2, G0, G1, B0, B1, Hsync, Vsync, DE in 7-bit serialized format).
6	RX0+	LVDS differential pair 0, positive.
7	GND	Ground between differential pairs.
8	RX1-	LVDS differential pair 1, negative. Carries the second data channel (R3, R4, R5, G2, G3, G4, B2, B3).
9	RX1+	LVDS differential pair 1, positive.
10	GND	Ground.
11	RX2-	LVDS differential pair 2, negative. Carries the third data channel (R6, R7, G5, G6, G7, B4, B5).
12	RX2+	LVDS differential pair 2, positive.
13	GND	Ground.
14	RXCLK-	LVDS clock pair, negative. The clock is typically 7 times the pixel clock frequency.
15	RXCLK+	LVDS clock pair, positive.
16	GND	Ground.
17	RX3-	LVDS differential pair 3 (optional, for 8-bit panels). Carries the fourth data channel (B6, B7, and spare bits).
18	RX3+	LVDS differential pair 3, positive.
19	GND	Ground.
20	NC	No connection, or sometimes used for backlight control.
21	NC	No connection.
22	BL_EN	Backlight enable signal (typically 3.3V logic, high to turn on the backlight inverter).
23	BL_PWM	Backlight brightness control (PWM signal, typically 0-3.3V, frequency around 200 Hz to 20 kHz).
24	GND	Ground for backlight control.
25	VLED+	Backlight power supply (usually 12V, but can be 5V or 24V depending on the panel).
26	VLED+	Same as pin 25, doubled for current.
27	VLED-	Backlight ground return.
28	VLED-	Same as pin 27.
29	GND	Additional ground.
30	GND	Additional ground.

This is a generic example, but many adapters have different pin assignments. For instance, some boards use a 40-pin connector for dual-channel LVDS, where pins 1-20 are for channel 0 and pins 21-40 are for channel 1, but the power and backlight pins are shared. The data mapping within the LVDS pairs follows the JEIDA or VESA standard. The VESA standard is more common in newer panels. In VESA mapping, the 7-bit serialized data within each differential pair is arranged as: Bit 0 = R0, Bit 1 = R1, Bit 2 = R2, Bit 3 = G0, Bit 4 = G1, Bit 5 = B0, Bit 6 = B1 for the first pair. The second pair: Bit 0 = R3, Bit 1 = R4, Bit 2 = R5, Bit 3 = G2, Bit 4 = G3, Bit 5 = G4, Bit 6 = B2. Third pair: Bit 0 = R6, Bit 1 = R7, Bit 2 = G5, Bit 3 = G6, Bit 4 = G7, Bit 5 = B4, Bit 6 = B5. Fourth pair (if 8-bit): Bit 0 = B6, Bit 1 = B7, Bit 2 = Hsync, Bit 3 = Vsync, Bit 4 = DE, Bit 5 = spare, Bit 6 = spare. The clock pair runs at the pixel clock frequency multiplied by 7. For a 1024x768 panel at 60 Hz, the pixel clock is about 65 MHz, so the LVDS clock is 455 MHz. That's a high-frequency signal, so the differential pairs must be impedance-matched to 100 ohms, and the cable length should be kept under 30 cm to avoid signal degradation.

The adapter's chipset determines the actual pinout. For example, the TFP401 from Texas Instruments is a popular HDMI receiver that outputs 24-bit parallel RGB data (24 bits per pixel, 3 bytes per pixel) along with horizontal sync, vertical sync, data enable, and pixel clock. This parallel bus then goes to an LVDS serializer, like the DS90C385 or a similar chip, which converts it into the differential pairs. The DS90C385 has 28 data inputs (for 24-bit color plus control signals) and outputs 4 differential data pairs plus a clock pair. The pinout of the adapter board is thus a direct mapping from the serializer's output pins to the connector. If you look at the datasheet of the DS90C385, the output pins are labeled TxOUT0+, TxOUT0-, TxOUT1+, TxOUT1-, etc. The adapter board's connector pins are wired to these. But the problem is that many Chinese-manufactured adapters don't follow a strict standard. I've seen boards where the power pins are swapped, or the backlight enable is on a different pin number. The only reliable way to know the pinout is to measure continuity with a multimeter between the LVDS connector pins and the known points on the board (like the chip's output pins or the power input).

Another critical factor is the voltage level. The LVDS signals are differential, with a typical swing of 350 mV (1.2V common mode). The power supply for the panel logic is usually 3.3V, but some older panels use 5V. The backlight power is often 12V, but it can be 5V for small panels or 24V for larger ones. The adapter board itself usually gets its power from the HDMI +5V pin, but that's only 5V at 50 mA, which is not enough to power a panel. So the adapter board typically has a separate power input, often a barrel jack or a 2-pin header, that supplies 12V (or the panel's required voltage). This 12V is then regulated down to 3.3V or 5V for the logic. The backlight power is usually passed through directly from the external supply. If you're using a panel that requires a specific voltage, you must set the adapter's jumper or solder bridge accordingly. Many adapters have a jumper to select between 3.3V and 5V for the LVDS power. Get this wrong, and you'll fry the panel's timing controller.

Let's talk about the EDID (Extended Display Identification Data) handling. The HDMI source reads the EDID from the adapter's EEPROM (usually a 24C02 or similar I²C EEPROM) to determine the supported resolutions and timings. The adapter's EDID is programmed to match the connected panel. If the adapter is generic, it might have a default EDID for a common resolution like 1366x768 or 1920x1080. If the panel's native resolution is different, you might need to reprogram the EDID via an I²C programmer. Some adapters have a flash memory that can be updated via a USB port. The pinout of the I²C bus (SCL and SDA) is on the HDMI connector (pins 15 and 16), and it's also often broken out on the adapter board for debugging. The hot plug detect pin (HDMI pin 19) is pulled high (to 5V) by the adapter when it's ready, which tells the source to read the EDID.

Now, let's get into the specific data rates and bandwidth. A single-channel LVDS can handle a maximum pixel clock of about 85 MHz, which corresponds to a resolution of 1366x768 at 60 Hz (with blanking, the pixel clock is about 85 MHz). For 1920x1080 at 60 Hz, the pixel clock is about 148.5 MHz, which exceeds the single-channel limit. That's why dual-channel LVDS is used for Full HD panels. Dual-channel LVDS splits the pixel data into two halves: odd pixels on channel 0, even pixels on channel 1, or left half on channel 0 and right half on channel 1, depending on the mapping. The dual-channel LVDS connector has 8 data pairs (4 per channel) and 2 clock pairs (one per channel). The total number of pins on the connector can be 40 or more. For example, a common 40-pin dual-channel LVDS pinout might have pins 1-10 for channel 0 data and clock, pins 11-20 for channel 1 data and clock, and the rest for power, ground, and backlight. But again, the pinout is not standardized. Some manufacturers use a 30-pin connector for dual-channel by multiplexing the power and ground pins.

I've worked with adapters based on the RTD2556 chip, which is an all-in-one HDMI-to-LVDS converter. This chip integrates the HDMI receiver, the LVDS serializer, and the backlight control. Its pinout for the LVDS output is fixed in the chip's datasheet, but the board layout determines which pins go to the connector. The RTD2556 supports both single and dual-channel LVDS, and it can be configured via I²C or strapping pins. The typical pinout for the RTD2556's LVDS output is: LVDS_CLKP/N (clock), LVDS_D0P/N, LVDS_D1P/N, LVDS_D2P/N, LVDS_D3P/N (for 8-bit), and for dual-channel, another set of the same. The chip also outputs a backlight enable and PWM signal. The connector pinout on the board is then a direct trace from these chip pins. If you have the board in hand, you can trace the PCB to find the exact mapping. But if you're buying a generic adapter, you have to rely on the seller's documentation, which is often incomplete or wrong. I've seen adapters advertised as "HDMI to LVDS for 15.6-inch laptop screen" that have a fixed pinout for a specific panel, but the seller doesn't provide the pinout diagram. In that case, you have to reverse-engineer it by comparing the board's silkscreen markings with known panel pinouts.

Another important detail is the backlight control. The LVDS connector usually includes pins for backlight enable (BL_EN) and backlight PWM (BL_PWM). The enable signal is a simple on/off logic level (0V for off, 3.3V for on). The PWM signal is a square wave with a duty cycle that controls the brightness. The frequency of the PWM signal is typically between 200 Hz and 20 kHz, depending on the inverter. Some adapters have a potentiometer or a jumper to set the PWM frequency. The backlight power (VLED+ and VLED-) is separate from the logic power. The current draw for the backlight can be several hundred milliamps to a few amps, depending on the panel size and LED configuration. For a 15.6-inch panel, the backlight might draw 300 mA at 12V (3.6 watts). For a 21.5-inch panel, it could be 600 mA at 12V (7.2 watts). The adapter's power supply must be able to handle this load. If you're using a laptop panel, the backlight is usually LED-based and requires a constant current driver, which is often built into the panel itself. The adapter just provides the power and control signals.

Let's look at the data mapping in more detail with a practical example. Suppose you have a 1366

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