PAM2841

Document number: DS36411 Rev. 2 - 2

11 of 15

www.diodes.com

October 2017

© Diodes Incorporated

PAM2841

Figure 3

4.

Using a Filtered PWM Signal

The filtered PWM signal can be considered as an adjustable DC voltage. Such regulated signal is often with some grade of ripple because of

some simple configuration of circuit. With appropriated arrangement of PWM frequency and level, and filter parameters, it can be used to replace

the variable DC voltage source in dimming control.

The circuit is shown in Figure 4.

Figure 4

Layout Consideration

As for all switching power supplies, especially those in high frequency and high current ones, layout is an important design step. If layout is not

carefully done, the regulator could suffer from instability as well as noise problems.

1.

Use separate traces for power ground and signal ground. Power ground and signal ground are connected together to a quite ground (input

connector).

2.

To prevent radiation of high frequency resonance, proper layout of the high frequency switching path is essential. Minimize the length and

area of all traces connecting to the SW pin. The loop including the PWM switch, Schottky diode and output capacitor, contains high current

rising and falling in nanosecond and thus it should be kept as short as possible.

3.

The input capacitor should be close to both the VIN pin and the GND pin in order to reduce the IC supply ripple.

4.

Keep the signal ground traces short and as close to the IC as possible. Small signal components should be placed as close as possible to the

IC, thus minimizing control signal noise interference.

VIN

ENA

L1

D1

C3

1µF

R1

910k

R2

27k

C1

10µF

C2

1µF

PGND

PGND

VIN

ENA

Comp

ENA

VIN

Comp

SW

OVP

FB

GND

R4

5k

R5

90k

R3

C4

10nF

SW

OVP

FB

GND

PAM2841

PAM2841

VIN

ENA

C1

10µF

L1

22µH

D1

C3

1µF

R1

910k

R2

27k

C2

1µF

R4

R5

90k

5k

R3

R6

C4

10nF

C5

100nF

10k

5V

0V

PWM

22µH