MCP1643
1 MHz Low Start-up Voltage Synchronous Boost
LED Constant Current Regulator
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
• Packages:
- MSOP-8
- 2x3 DFN-8
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
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.
Package Types
MCP1643
MSOP-8
MCP1643
2x3 DFN*
EN 1
VFB 2
NC 3
VOUT 4
8 VIN EN 1
8 VIN
7 SGND VFB 2 EP 7 SGND
6
PGNDVONUCT
3
4
9
6 PGND
5 SW
5 SW
* Includes Exposed Thermal Pad (EP), see Table 3-1.
2013 Microchip Technology Inc.
DS20005208A-page 1
