MCP1650 Multiple White LED Demo Board User’s Guide
DS51586A-page 6 © 2005 Microchip Technology Inc.
1.2 WHAT IS THE MCP1650 MULTIPLE WHITE LED DEMO BOARD?
The MCP1650 Multiple White LED Demo Board demonstrates the use of a conven-
tional boost topology in a LED application. The board also serves as a platform to
evaluate the MCP1650 boost controller.
Since designers are tasked with improving efficiency, lowering cost and decreasing
size, white LEDs are now being used. Powering white LEDs, which have a forward drop
(V
F
) of 3.6V, typically becomes more difficult when the application requires multiple
LEDs. It also requires the output current to be maintained constant with the degrading
battery life and temperature variation. In the MCP1650 Multiple White LED Demo
Board, a solution using the MCP1650 is discussed and shown to be greater than 80%
efficient and also controls the intensity of the LEDs through the PIC10F microcontroller.
The intensity of the LEDs can be controlled through a momentary switch.
The MCP1650 Multiple White LED Demo Board demonstrates the use of the PIC10F
microcontroller in controlling the intensity of the nine white LEDs connected in series.
The board also serves the purpose of evaluating the MCP1650 device.
The design of the demo board is done with boost controller IC MCP1650, which is
capable of generating an output voltage of over 100V. The MCP1650 family has numer-
ous features that include soft-start operation, peak inductor current monitoring, scal-
able external MOSFET, a shutdown pin for external control, low battery detect and a
power good output. The MCP1650 can be configured in either, the conventional boost
topology (Figure 1-1), a boot-strapped boost topology or a SEPIC topology. The output
voltage of the boost converter is determined by the number of LEDs being driven and
accordingly, the external MOSFET, Schottky diode and the output capacitor need to be
selected.
The feedback voltage (V
FB
) for the MCP1650 is 1.22V. This is only 4% of the total out-
put voltage when powering nine white LEDs. When the voltage developed across the
sense resistor (R
SENSE
) is below the internal reference voltage, the internal oscillator
is gated on and the external N-channel MOSFET is pulsed on and off to transfer energy
from the source to the load. This continues until the voltage across R
SENSE
is above
the 1.22V threshold, gating off the internal oscillator.
1.3 WHAT THE MCP1650 MULTIPLE WHITE LED DEMO BOARD KIT INCLUDES
This MCP1650 Multiple White LED Demo Board kit includes:
• MCP1650 Multiple White LED Demo Board
• MCP1650 Multiple White LED Demo Board User’s Guide
