CAT32 datasheet(9/14 Pages) CATALYST

9 / 14 page

CAT32

Doc. No. MD-5001 Rev. AD

Characteristics subject to change without notice

LED DIMMING WITH A LOGIC SIGNAL

For applications that need to adjust the LED

brightness in discrete steps, a logic signal can be

used. RMIN sets the minimum LED current value

(when the NMOS is OFF):

RINCR determines how much LED current increases

when the external NMOS switch is turned ON.

LED DIMMING WITH A DC VOLTAGE

PCB Layout Guidelines

The CAT32 is a high-frequency switching regulator

and therefore proper PCB board layout and

component placement can minimize noise and

radiation and increase efficiency. To maximize

efficiency, the CAT32 design has fast switch rise and

fall times. To prevent radiation and high frequency

resonance problems minimize the length and area of

all traces connected to the SW pin and use a ground

plane under the switching regulator.

The switch, schottky output diode and output

capacitor signal path should be kept as short as

possible. The ground connection for the RSET resistor

should be tied directly to the GND pin and not be

shared with other components.

)

MIN

(

LED

MIN

255

)

Increase

(

LED

INCR

255

–

225

)

MIN

(

LEAD

)

MAX

(

LED

MAX

ADJ

CAT32

SHDN

PWM

CAT32

RSET

PWM

RPWM

RSET

CAT32

RSET

VDC

RSET

RADJ

RPWM

CAT32

RSET

PWM

10kΩ

0.1µF

RSET

RMIN

CAT32

RSET

RINCR

Logic

Signal

Figure 3. LED Dimming Circuits

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