PMIC Circuit

 Deep Knowledge About PMIC Circuits Used in LCD TV Panels By Imran Ashraf 

Power Management Integrated Circuits (PMICs) are critical components in **LCD TV panels**, responsible for efficiently managing and distributing power to various subsystems such as the **T-Con board (Timing Controller), backlight LEDs, source/gate drivers, and audio/video processing chips**. Below is a detailed breakdown of their functions, architecture, and key considerations.

1. Role of PMIC in LCD TVs

PMICs in LCD TVs perform several essential functions:

Voltage Regulation: Converts input power (e.g., 12V/24V from SMPS) to required voltages (1.8V, 3.3V, 5V, ±15V, etc.).

Power Sequencing: Ensures correct startup/shutdown order to prevent latch-up or damage.

Backlight Driver Control: Manages LED backlight current (constant current drivers for mini-LED/OLED).

Efficiency Optimization  :Uses **buck, boost, and LDO regulators** to minimize power loss.

Protection Circuits: Overvoltage (OVP), overcurrent (OCP), and thermal shutdown (TSD).

2. Key PMIC Sub-Blocks in LCD TVs

A. DC-DC Converters (Buck/Boost)

Buck Converters  Step down voltage (e.g., 12V → 5V for T-Con).

-Boost Converters: Step up voltage (e.g., 12V → 24V for gate drivers).

- Synchronous vs. Non-Synchronous: Synchronous designs improve efficiency (>90%).

B. LED Backlight Drivers

Constant Current Drivers : For LED strings (PWM dimming control).

- Mini-LED Local Dimming  Requires multiple channels (up to 1000+ zones in high-end TVs).

-OLED TV PMICs**: Use **high-voltage boost converters** (up to 60V for OLED panel bias).

C. LDOs (Low-Dropout Regulators)**

- Used for noise-sensitive circuits (e.g., T-Con logic, audio ICs).

- **Low noise & high PSRR** (Power Supply Rejection Ratio) for stable video signals.

D. Power Sequencing Controller**

- Ensures proper startup sequence (e.g., **T-Con before source drivers**).

- Prevents inrush current and voltage spikes.

E. Protection & Monitoring**

- **OVP/OCP/UVLO (Under-Voltage Lockout)**.

- **I²C/SPI Interface** for digital control and fault reporting.

3. Advanced PMIC Features in Modern LCD TVs**

A. Dynamic Voltage Scaling (DVS)**

- Adjusts voltage based on load (saves power in dark scenes).

- Used in **high-refresh-rate (120Hz/144Hz) panels**.

B. Digital Power Management (Digital PMICs)**

- **Programmable via I²C/SPI** (e.g., adjusting backlight dimming curves).

- Supports firmware updates for adaptive power control.

C. Integration with T-Con & Source Drivers**

- Some PMICs integrate **gamma voltage buffers** for precise panel control.

-eDP (Embedded DisplayPort) PMICs** manage power for high-resolution displays.

D. Thermal Management**

- **Smart heat dissipation** via load balancing.

- **Junction temp monitoring** to prevent overheating

4. Common PMIC ICs Used in LCD TVs

| Manufacturer| PMIC Model | Key Features** |

|-----------------|--------------|-----------------|

Texas Instruments | TPS651xx | Dual-output (+15V/-15V) for T-Con |

Maxim Integrated| MAX171xx | High-efficiency LED drivers |

ON Semiconductor | FAN534x | Boost converter for OLED bias 

Richtek| RT693x | Multi-channel backlight driver 

Dialog Semiconductor | DA921x | Digital multi-phase buck converter |

Design Challenges & Solutions

EMI Issues

Spread-spectrum clocking (SSC) in DC-DC converters to reduce noise.

Shielding & proper PCB layout (minimize high-frequency loops).

Power Efficiency

Synchronous rectification  vs. diode-based designs.

Light-load efficiency modes (PWM/PFM switching).

Mini-LED & Local Dimming Complexity

- Requires multi-channel PMICs with precise current matching.

-Hybrid dimming (PWM + analog) for smooth brightness transitions.

Heat Dissipation

Thermal vias & heatsinks for high-current paths.

Dynamic power throttling** in high-temperature conditions.

6. Future Trends in TV PMICs

GaN (Gallium Nitride) PMICs for higher efficiency and compact designs.

AI-based power optimization (adjusts voltages based on content).

- **Fully integrated PMIC + T-Con SoCs** for slimmer designs.

Conclusion

PMICs in LCD TVs are evolving with **higher integration, digital control, and advanced backlight management**. Understanding their architecture helps in troubleshooting power-related display issues (e.g., flickering, no backlight) and optimizing TV power consumption.