Integrated Multi-Channel DC/DC Converter for TFT LCD Panels


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The RT9921 includes a high-performance boost regulator, a low dropout linear regulator (LDO), a gate pulse modulator (GPM), a voltage detector, a VCOM buffer (unity-gain OPA), and a VGH charge pump controller for active-matrix thin-film transistor (TFT) liquid-crystal displays (LCDs).

The boost converter provides the regulated supply voltage for the panel source driver ICs. The converter is a high switching frequency (640kHz or 1.2MHz) current-mode regulator with an integrated 16V N-Channel 0.2W MOSFET that allows the use of ultra-small inductors and ceramic capacitors. It provides fast transient response to pulsed loading while achieving efficiency over 90%. The device can produce output voltage as high as 15V from an input as low as 2.5V. Soft-Start is programmed by external capacitor, which sets the input-current ramp-rate.

The low-dropout (LDO) linear regulator can supply up to 350mA current while input voltage is 3.3V. It uses an internal P-MOSFET as the pass device. It is suitable for the supply voltage of the timing controller.

The GPM is controlled by frame signals from timing controller to modulate the Gate-On voltage, VGHM, which acts a flicker compensation circuit to reduce the coupling effect between gate lines and pixels. It also can delay the Gate-On voltage while power-on for achieving a corrected power-on sequence for gate driver ICs. Both of power-on delay time and the falling time of the Gate-On voltage are programmable by external capacitor and resistor.

The voltage detector monitors the supply voltage to issue a reset signal while the detected voltage is too low. The detecting level is decided by an external resistor divider and the delay time is programmable by an external capacitor.

The VCOM buffer can drive the LCD VCOM voltage that features high short-circuit current (140mA), fast slew rate (12V/μs), wide bandwidth (12MHz) and rail-to-rail inputs and outputs.

The VGH charge pump controller provides regulated TFT Gate-On voltage. The regulation of the positive charge pump is generated by the internal comparator that senses the output voltage and compares it with an internal reference.


Key Spec.
RT9921 RT9921A
Status Active Active
Vin (min) (V) 2.5 2.5
Vin (max) (V) 5.5 5.5
Number of Channels 5 5
Number of Buck Converters 0 0
Number of Boost Converters 1 1
Number of Negative Outputs 1 1
Number of LED Drivers 0 0
Number of LDO Regulators 1 1
Application LCD Bias LCD Bias
Features Adjustable Frequency;Adjustable Soft-Start;Current Mode Control;Cycle-by-Cycle Current Limit;OCP;UVP Adjustable Frequency;Adjustable Soft-Start;Current Mode Control;Cycle-by-Cycle Current Limit;OCP;UVP
Package Type VQFN-4x4-24 VQFN-4x4-24
  • 2.5V to 5.5V Input Supply Voltage
  • 640kHz/1.2MHz Current-Mode Boost Regulator
    ► Fast Transient Response to Pulsed Load
    ► Adjustable Output Voltage (±1%)
    ► Built-In 16V, 2A, 0.2Ω N-MOSFET
    ► High Efficiency Up to 90%
    ► Programmable Soft-Start
    ► Over-Current Protection
    ► Output Under-Voltage Protection
  • Low Dropout Voltage Linear Regulator
    ► Adjustable Output Voltage : 1.5V to VIN - 0.5V
    ( ±1.5%)
    ► Maximum Output Current : 350mA
  • On-Chip GPM Controller with Adjustable
    ► Falling Time and Power-On Delay
    ► Flicker Compensator
    ► Power-On Sequence Control
  • Low Voltage Detector
    ► Programmable Detecting Voltage (±2%) and Delay Time
  • Unity-Gain Operation Amplifier for VCOM Buffer
  • Charge Pump for VGH regulation
  • Over-Temperature Protection
  • Thin 24 Lead VQFN Package
  • RoHS Compliant and 100% Lead (Pb)-Free
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Integrated Multi-Channel DC/DC Converter for TFT LCD Panels2019/04/10