CAT32

9

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):

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

should be tied directly to the GND pin and not be

shared with other components.

)

MIN

(

LED

MIN

I

V

1

.

0

×

255

=

R

)

Increase

(

LED

INCR

I

V

1

.

0

×

255

=

R

I

–

I

V

1

.

0

–

V

×

225

=

R

)

MIN

(

LEAD

)

MAX

(

LED

MAX

ADJ

CAT32

SHDN

5

PWM

CAT32

RSET

4

PWM

CAT32

RSET

4

CAT32

RSET

PWM

10kΩ

0.1µF

4

CAT32

RSET

Logic

Signal

4

Figure 3. LED Dimming Circuits