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ADM00555

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
MCP1662 LED DRIVER
EVALUATION BOARD
USER’S GUIDE
2014 Microchip Technology Inc. DS50002285A-page 13
Chapter 2. Installation and Operation
2.1 INTRODUCTION
The MCP1662 has been developed for applications that require driving a string of LEDs
from a low-voltage source. Using a peak current mode control the MCP1662 offers
good line and load step responses over a wide output range (up to 32V total output volt-
age or 10 white LEDs). The integration of compensation and protection circuitry is an
important feature that minimizes the required number of additional components.
FIGURE 2-1: MCP1662 Boost 30, 60, 90 mA Constant Current Application.
2.2 FEATURES
The MCP1662 LED Driver Evaluation Board has the following features:
• It can be powered by two-cell Alkaline, NiCd, NiMH or Lithium AA cell batteries
• Input Voltage range (V
IN
): 2.4V to 5.5V, with V
IN
V
OUT
• Undervoltage Lockout: 2.3V to Start; 1.85V to Stop
• Adjustable Output Current: 30 mA, 60 mA or 90 mA, selected using a dual switch
on-board
• PWM Switching Frequency: 500 kHz
• Enable converter using switch on board
• 1.3A Peak Input Current Limit
• Overtemperature Protection (if the die temperature exceeds +150°C, with 15°C
hysteresis)
• Open Load Protection in case of: LED fail or FB disconnected/fault
+
-
ULT LITHIUM
+
-
ULT LITHIUM
V
IN
GND
V
FB
SW
EN
MCP1662
C
IN
10 µF
C
OUT
10 µF
L
4.7
µH
RB
1
RB
2
RB
3
101010
R
EN
1 M
1.85V to 3.4V
Note: The application will typically start if the voltage on the batteries is above 2.3V and will
continue to operate down to 1.85V.
EN
Switch
Current
Switch
Selector
MCP1662 LED Driver Evaluation Board User’s Guide
DS50002285A-page 14 2014 Microchip Technology Inc.
2.3 GETTING STARTED
The MCP1662 LED Driver Evaluation Board is fully assembled and tested to evaluate
and demonstrate the MCP1662 product. This board requires the use of external lab
supplies or two AA batteries.
2.3.1 Power Input and Output Connection
2.3.1.1 POWERING THE MCP1662 LED DRIVER EVALUATION BOARD
Soldered test points are available for input voltage connections. The maximum input
voltage should not exceed 5.5V. The output current will not remain in regulation for
input voltages that are greater than or equal to the forward voltage of the LEDs.
The MCP1662 LED Driver Evaluation Board was designed to help the engineer
validate the MCP1662 device. The package selected for the MCP1662 LED Driver
Evaluation Board is 5-Lead SOT-23.
SW1 is the enable switch, which gives the state of the converter, On or Off. A soldered
test point is also available for the EN pin, that can be used for PWM dimming. The
second switch is used to modify the value of the sense resistor, in order to modify the
LED current and achieve analog dimming.
2.3.1.2 BOARD POWER UP PROCEDURE:
1. Connect input supply as shown in Figure 2-2 or insert two AA batteries in the bat-
tery holder on the bottom side of the board. Respect the polarity of the batteries.
2. Using the EN switch, the state of the converter is changed from On to Off.
3. Change the value of the output current using the Current Switch Selector. There
are three available currents: 30 mA, 60 mA and 90 mA. When changing the posi-
tions of the Current Switch Selector, the value of the sense resistor is modified
and the brightness of the LEDs change.
Additional test points are available to visualize different signals (SW, output current,
FB) or to modify the output current by dimming, using the EN pin.
FIGURE 2-2: MCP1662 LED Driver Evaluation Board Setup.
Installation and Operation
2014 Microchip Technology Inc. DS50002285A-page 15
2.3.1.3 ADJUSTABLE LED CURRENT BY RECALCULATING THE SENSE
RESISTOR (ANALOG DIMMING)
The Sense Resistor (R
SET
) is used to modify the value of the output current. The value
for the resistor can be calculated using Equation 2-1:
EQUATION 2-1:
2.3.1.4 ADJUSTABLE LED CURRENT BY USING THE EN PIN (PWM DIMMING)
The MCP1662 allows PWM dimming by turning the LED on and off with a variable duty
cycle PWM signal applied to the EN pin. The maximum frequency for dimming is limited
by the start-up and the load. By varying the duty cycle of the PWM signal applied on
the EN input, the LED current changes linearly. An example of PWM dimming can be
observed in Figure 2-3.
By removing the 0 Ohms R1 Resistor, the soldered connectors (J3 and J4) can be used
to either insert a multimeter to measure the LED current or to create a loop through
which, with the help of an oscilloscope current probe, the current through the LED can
be visualized.
FIGURE 2-3: PWM Dimming with MCP1662.
R
SET
V
FB
I
LED
-----------=
Where: V
FB
= 0.300V
Note: If the Sense Resistor is recalculated, the Current Switch Selector will not
have the same functionality, as the Sense Resistor will add a resistor in par-
allel with the calculated component and the value of the current will be dif-
ferent than the one specified in the User Guide. The Sense Resistor will be
used in place of the RB
X
resistors.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22

ADM00555

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Manufacturer:
Microchip Technology
Description:
LED Lighting Development Tools MCP1662 Evaluation Board
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