How to Distinguish VCC, IOVCC, and VDD in Small and Medium-Sized LCD Panel Hardware Design

    In the design of small and medium-sized LCD panels, hardware engineers often encounter difficulties in understanding the differences between VCC, VDD, and IOVCC.  Here, Shenzhen Hongjia Technology provides some explanation:

In general, the key difference lies in the different components they power.

ONE. Summary of Key Differences

Name Full Name and Meaning Power Supply Target Typical Voltage Function

VCC Voltage to the Common Collector (originally used in TTL circuits) The "analog" part of the entire screen (e.g., backlight driver circuit, level shifter) High, e.g., 5V, 12V Provides power to the core analog circuits and high-voltage parts of the screen

VDD Voltage to the Drain of the MOSFET (originally used in CMOS circuits) The core digital logic of the screen driver IC (e.g., timing controller, row/column driver) Low, e.g., 1.8V, 3.3V Provides the core operating voltage for the screen's "brain" (digital chip)

IOVCC Input/Output Voltage (or VCI) The voltage level of the screen interface (e.g., LCD pins, I/O ports for communication with the controller) Commonly 1.8V or 3.3V Ensures communication level compatibility between the screen and the main controller chip (e.g., CPU)

TWO. Detailed Explanation

1. VCC (Analog Power)

· What it is: VCC usually refers to the main power supply input. It supplies power to the analog circuits within the LCD panel that require higher voltage.

· Why it's needed: Some modules inside the screen, such as the backlight LED driver circuit, gamma correction circuit, and level shifter (which converts low-voltage digital signals into high-voltage analog signals to control the liquid crystal molecules), require higher voltage than digital logic circuits.

· Characteristics: Higher voltage, potentially higher current. For example, a screen might require 12V VCC to drive its backlight circuit.

2. VDD (Digital Core Power)

· What it is: VDD usually refers to the digital core voltage. It supplies power to the digital logic circuits inside the LCD driver chip (such as the Source Driver, Gate Driver, and T-Con). • Why it's needed: Modern chips are based on CMOS technology, and their core components (CPU, logic gates, memory, etc.) operate at lower voltages to reduce power consumption. This voltage is VDD.

• Characteristics:  It's a relatively low voltage, evolving with semiconductor technology (e.g., 3.3V -> 1.8V -> 1.2V). It's the power the chip needs to "think."

3. IOVCC (Interface Power)

• What it is: IOVCC specifically refers to the voltage for the input/output interface. It determines the logic level standard used for communication between the screen and the external controller chip (e.g., your phone's processor or microcontroller).

• Why it's needed: To ensure successful communication, both sides must use the same "language," i.e., the same voltage levels to represent "0" and "1."

• If the controller chip's GPIO port is 1.8V, then the screen's IOVCC must also be 1.8V.

• If the controller is 3.3V, then IOVCC must be 3.3V.

• Characteristics: Level matching is crucial. Connecting the wrong IOVCC voltage will likely result in communication failure or even damage to the interface circuitry.

THREE. A Simple Analogy

Imagine a LCD screen as a computer:

• VCC is like the computer's main power supply, powering the entire system (including power-hungry components like the graphics card and fan).

• VDD is like the voltage powering the CPU core (very precise and low voltage).

• IOVCC is like the voltage standard for USB and Ethernet ports; it ensures your computer can communicate with external devices (like a USB drive or router) using the correct "voltage language."

FOUR. Practical Considerations

1. Consult the Datasheet: Different LCD screen models may have subtle differences in the definitions and allowed voltage ranges for these three pins. Never assume anything; always strictly follow the official datasheet.

2. Power-on Sequence: In some complex systems, there may be strict requirements for the power-on and power-off sequence of VCC, VDD, and IOVCC to avoid latch-up or communication errors. This will be specified in the datasheet. 3. Power Supply Quality: These power supply pins typically require a very stable and clean (low-noise) power source. Appropriate decoupling capacitors (such as a 100nF ceramic capacitor and a 10µF tantalum capacitor) should usually be added to the design for this purpose.

    We hope the above explanation helps you fully understand the differences!