Simplified Block Diagram
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- +4.5V to +5.5V Input-Voltage Range
- Output Voltages
- +14V Output at 700mA (Step-Up Switching Regulator)
- +28V Output at 50mA (Positive Charge Pump)
- -9V Output at 50mA (Negative Charge Pump)
- Three High-Current Op Amps (±180mA)
- 1.2MHz Switching Frequency
- All Output Voltages are Resistor Adjustable
- Logic-Controlled, High-Voltage Switch
- High-Voltage Stress Mode for the Step-Up and Positive Charge-Pump Output Voltages
- Capacitor-Controlled Initial Startup Delay and Positive Charge-Pump Delay
- Low-Profile Surface-Mount Components
- Fully Assembled and Tested
- LCD TVs and LCD Monitors
The EV kit operates from a DC supply voltage of +4.5V to +5.5V, as configured. The step-up switching regulator is configured for a +14V output providing at least 700mA. The positive charge pump is configured for a +28V output providing at least 50mA. The negative charge pump is configured for a -9V output providing at least 50mA. The three high-current op amps are each configured for a +7V output that can source or sink 180mA. The high-voltage switch can be controlled by external logic. The EV kit's input voltage range can be lowered to +4V at slightly lower load currents.
The MAX8784 step-up switching regulator operates at 1.2MHz, allowing the use of tiny surface-mount components. The MAX8784 thin QFN package (0.8mm max height), with low-profile external components, allows this circuit to be less than 3mm high.