Overview
The LP8557AYFQT, produced by Texas Instruments, is a high-efficiency LED driver designed for backlighting applications in tablets and similar devices. This component integrates a DC-DC inductive boost converter and six high-precision current sinks, making it highly efficient and versatile. The LP8557 is available in two variants: the LP8557, which uses a pulse width modulated (PWM) signal for brightness control, and the LP8557I, which adds support for I2C communication. This allows for more flexible and precise control over the backlighting system.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| Input Voltage Range (VDD) | 2.7 | 5.5 | V | |
| Standby Current (IDDQ) | 1 | µA | ||
| Operating Current (IDD) | 2.2 | mA | ||
| Internal Oscillator Frequency Accuracy | -4% | 4% | 7% | % |
| Thermal Shutdown Threshold (TTSD) | 150 | °C | ||
| Maximum Sink Current (ILED_MAX) | 25 | mA | ||
| LED Current Accuracy (ILED_ACC) | -4% | 4% | % | |
| PWM Frequency (ƒPWM) | 75 | 25000 | Hz |
Key Features
- Integrated DC-DC Inductive Boost Converter: With adaptive output voltage control to minimize power consumption.
- Six High-Precision Current Sinks: Each capable of sinking up to 25 mA of current.
- Adaptive Current Sink Headroom Voltage Control: Scales the headroom voltage with the LED current for optimal system efficiency.
- LED String Count Auto-Detect: Enables the use of the same device in systems with 1 to 6 LED strings for maximum design flexibility.
- Hybrid PWM Plus Current Dimming: Combines PWM dimming and LED current-dimming control methods for better optical efficiency.
- Phase Shift PWM Mode: Reduces audible noise and allows for smaller boost output capacitors.
- Flexible CABC Support: Combines brightness level selections based on PWM input and I2C commands.
- Programmable Boost SW Slew Rate Control and Spread Spectrum Scheme: For reduced switching noise and improved EMI performance.
- Fault Detection: Includes input undervoltage lockout, thermal shutdown, overcurrent protection, overvoltage protection, and LED open and short detection.
Applications
The LP8557AYFQT is primarily designed for backlighting applications in tablets and other portable devices. Its high efficiency, precision current control, and adaptive features make it an ideal choice for systems requiring reliable and efficient LED backlight management.
Q & A
- What is the input voltage range of the LP8557AYFQT?
The input voltage range is from 2.7 V to 5.5 V.
- How many high-precision current sinks does the LP8557AYFQT have?
The LP8557AYFQT has six high-precision current sinks.
- What is the maximum sink current per LED current sink?
The maximum sink current per LED current sink is 25 mA.
- Does the LP8557AYFQT support I2C communication?
The LP8557I variant supports I2C communication, while the LP8557 variant does not.
- What is the purpose of the adaptive boost voltage and LED current sink headroom controls?
These controls minimize power consumption by adjusting the voltage to the lowest sufficient level under all conditions and scaling the headroom voltage with the LED current for optimal system efficiency.
- How does the phase shift PWM mode benefit the system?
The phase shift PWM mode reduces audible noise and allows for smaller boost output capacitors.
- What types of fault detection does the LP8557AYFQT include?
The device includes input undervoltage lockout, thermal shutdown, overcurrent protection, overvoltage protection, and LED open and short detection.
- Can the LP8557AYFQT auto-detect the number of LED strings connected?
Yes, the LP8557AYFQT can auto-detect the number of LED strings attached and adjust the phasing of the remaining current sinks accordingly.
- How does the hybrid PWM plus current dimming control work?
This control combines PWM dimming and LED current-dimming control methods to achieve better optical efficiency and smooth brightness control.
- What is the purpose of the programmable boost SW slew rate control and spread spectrum scheme?
These features reduce switching noise and improve EMI performance.
