MCP1643
1 MHz Low Start-up Voltage Synchronous Boost
LED Constant Current Regulator
Features
Description
• 1.6A Typical Peak Input Current Limit
• Up to 550 mA LED Load Current
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 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
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.
- 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
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.
• Inrush Current Limiting
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.
• Internal Soft-Start (240 µs typical)
• Shutdown (EN = GND):
- True Load Disconnect
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.
- Dimming Control by Variable Duty Cycle
• Shutdown Current: 1.2 µA (typical)
• Overtemperature protection
• Packages:
- MSOP-8
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.
- 2x3 DFN-8
Applications
The device also features a thermal shutdown at
+150°C, with +25°C hysteresis.
• One and Two Cell Alkaline and NiMH/NiCd
Portable LED Lighting Products
Two package options, MSOP-8 and 2x3 DFN-8, are
available.
• LED Flashlight and Head Lamps
• Rechargeable Flashlights
Package Types
• Wall LED Lamps with Motion Detectors
• LED supply for backlights
MCP1643
MCP1643
MSOP-8
2x3 DFN*
• General LED constant current applications
VIN
EN
1
8
7
6
5
EN
VIN
1
8
VFB
SGND
2
3
4
7
6
5
SGND
EP
9
V
FB 2
NC
PGND
SW
3
4
NC
VOUT
PGND
SW
VOUT
* Includes Exposed Thermal Pad (EP), see Table 3-1.
2013 Microchip Technology Inc.
DS20005208A-page 1