LED step-up regulator, 0.5 ... 5 Vin, 1 MHz, 5 Vout, MSOP-8

MCP1643, 1 MHz Low Start-up Voltage Synchronous Boost LED Constant Current Regulator

Description:
MCP1643 is a compact, high-efficiency, fixed frequency, synchronous step-up converter optimized to drive one LED with constant current, that operates from one and two-cell alkaline and NiMH/NiCd batteries. The device can also drive two red/green/yellow series connection LEDs. Low-voltage technology allows the regulator to start up without high-output voltage and load-current overshoot from a low 0.65V input. High efficiency is accomplished by integrating the low resistance N-Channel Boost switch and synchronous P-Channel switch. All compensation and protection circuitry are integrated to minimize external components. The internal feedback (VFB) voltage is set to 120 mV for low power dissipation when sensing and regulating LED current. A single resistor sets the constant current output that drives the LED load. The device features an output overvoltage protection that limits the output voltage to 5.0V typical, in case the LED fails or output load is disconnected. The LED will either be turned OFF or turned ON using the enable input. A True Output Load Disconnect mode provides input-to-output isolation while Shutdown (EN = GND) by removing the normal boost regulator diode path from input to output. Shutdown state consumes 1.2 µA from input at room temperature. The LED can be turned on and off with a variable duty cycle pulse-width modulation (PWM) signal applied to the EN pin for dimming applications. The device also features a thermal shutdown at +150°C, with +25°C hysteresis. Two package options, MSOP-8 and 2x3 DFN-8, are available.

Features:
- 1.6A Typical Peak Input Current Limit
- Up to 550 mA LED Load Current
- Low Start-up Voltage: 0.65V (typical, 25 mA LED Current)
- Low Operating Input Voltage: down to 0.5V
- Maximum Input Voltage < VLED < 5.0V
- Maximum Output Voltage:
- 5.0V
- Overvoltage Protection
- Low Reference Voltage:
- VFB = 120 mV
- Minimal Power Loss on Sense Resistor
- Pulse-Width Modulation Mode Operation (1 MHz)
- Internal Synchronous Rectifier
- Internal Compensation
- Inrush Current Limiting
- Internal Soft-Start (240 µs typical)
- Shutdown (EN = GND):
- True Load Disconnect
- Dimming Control by Variable Duty Cycle
- Shutdown Current: 1.2 µA (typical)
- Overtemperature protection

Typical Applications
- One and Two Cell Alkaline and NiMH/NiCd Portable LED Lighting Products
- LED Flashlight and Head Lamps
- Rechargeable Flashlights
- Wall LED Lamps with Motion Detectors
- LED supply for backlights
- General LED constant current applications