Installation and Operation

 2015 Microchip Technology Inc.

DS50002363A-page 15

2.3.1.3

ADJUSTING LED CURRENT BY RECALCULATING THE SENSE

RESISTOR (ANALOG DIMMING)

The sense resistor is used to modify the value of the output current. The value for the

resistor can be calculated using the following equation:

EQUATION 2-1:

SENSE RESISTOR CALCULATION

Figure 2-3 shows the maximum output current for four LEDs:

FIGURE 2-3:

Maximum Output Current vs. Input Voltage.

For the MCP1664 LED Driver Evaluation Board, if the current select switch is set to

90 mA, the input voltage range varies from 2.4V to 5.5V; when the current select

switch is set to 180 mA, the input voltage range is from 3V to 5.5V; when the current

select switch is set to 270 mA, the input voltage range runs from 4.5V to 5.5V

Where:

RSENSE

VFB

ILED

--------------

=

Note: If the sense resistor is recalculated, the switch used for current selecting will

not be used, as it will add a resistor in parallel with the calculated compo-

nent and the value of the current will be different than the one specified in

the User Guide.