Multi-Output Power Supply with VCOM Amplifier and High-Voltage Gamma Reference for LCD TVs

The MAX17114 generates all the supply rails for thin-film transistor liquid-crystal display (TFT LCD) TV panels operating from a regulated 12V input. It includes a step-down and a step-up regulator, a positive and a negative charge pump, an operational amplifier, a high-accuracy, high-voltage gamma reference, and a high-voltage switch control block. The MAX17114 can operate from input voltages from 8V to 16.5V and is optimized for an LCD TV panel running directly from 12V supplies.

The step-up and step-down switching regulators feature internal power MOSFETs and high-frequency operation allowing the use of small inductors and capacitors, resulting in a compact solution. The step-up regulator provides TFT source driver supply voltage, while the step-down regulator provides the system with logic supply voltage. Both regulators use fixed-frequency current-mode control architectures, providing fast load-transient response and easy compensation. A current-limit function for internal switches and output-fault shutdown protects the step-up and step-down power supplies against fault conditions. The MAX17114 provides soft-start functions to limit inrush current during startup. In addition, the MAX17114 integrates a control block that can drive an external p-channel MOSFET to sequence power to source drivers.

The positive and negative charge-pump regulators provide TFT gate-driver supply voltages. Both output voltages can be adjusted with external resistive voltage-dividers. A logic-controlled, high-voltage switch block allows the manipulation of the positive gate-driver supply. The MAX17114 includes one high-current operational amplifier designed to drive the LCD backplane (VCOM). The amplifier features high output current (±200mA), fast slew rate (45V/µs), wide bandwidth (20MHz), and rail-to-rail outputs.

Also featured in the MAX17114 is a high-accuracy, high-voltage adjustable reference for gamma correction.

The MAX17114 is available in a small (7mm x 7mm), ultra-thin (0.8mm), 48-pin, TQFN-EP package and operates over the -40°C to +85°C temperature range.

Applications

* LCD TV Panels

* 8.0V to 16.5V IN Supply-Voltage Range

* Selectable Frequency (500kHz/750kHz)

* Current-Mode Step-Up Regulator

* Fast Load-Transient Response

* High-Accuracy Output Voltage (1.0%)

* Built-In 20V, 3.5A, 100mΩ MOSFET

* High Efficiency

* Adjustable Soft-Start

* Adjustable Current Limit

* Low Duty-Cycle Operation (13.2VIN - 13.5V AVDD)

* Current-Mode Step-Down Regulator

* Fast Load-Transient Response

* Built-In 20V, 3.2A, 120mΩ MOSFET

* High Efficiency

* 3ms Internal Soft-Start

* Adjustable Positive Charge-Pump Regulator

* Adjustable Negative Charge-Pump Regulator

* Integrated High-Voltage Switch with Adjustable Turn-On Delay

* High-Speed Operational Amplifier

* ±200mA Short-Circuit Current

* 45V/µs Slew Rate

* High-Accuracy Reference for Gamma Buffer

* ±0.5% Feedback Voltage

* Up to 30mA Load Current

* Low-Dropout Voltage 0.5V at 60mA

* External p-Channel Gate Control for AVDD Sequencing

* XAO Comparator

* Input Undervoltage-Lockout and Thermal-Overload Protection

* 48-Pin, 7mm x 7mm, Thin QFN Package