PAM2841

Document number: DS36411 Rev. 2 - 2

10 of 15

www.diodes.com

October 2017

© Diodes Incorporated

PAM2841

Figure 1

2.

Using an External PWM Signal to NMOS Gate

When PWM signal is at high level, N MOSFET turned on, then pull Comp pin down, then the LED current should be zero. When PWM signal is at

low level, N MOSFET turned off. The circuit uses resistor R1 to set the on state current. The average LED current changes proportionally with the

duty cycle of the PWM signal. A 100% duty cycle turns off the PAM2841 and leads to zero LED current. A 0% duty cycle generates full current.

Also the recommend frequency is between 100 and 500Hz. Frequency<100Hz can naturally cause LEDs to blink visibly.

Figure 2

3.

Using a DC Voltage

For some applications, a simple and direct way to control brightness is using an external variable DC voltage to vary the voltage drop on feedback

resistor. This will make the PAM2841 adjust the output current to follow the change of feedback voltage. The circuit is shown in Figure 3. As the

DC voltage increases, the voltage drop on R4 increases and the voltage drop on R3 decreases. Thus, the LED current decreases. The selection

of R4 and R5 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin current. For

VCC range from 0V to 2V, the selection of resistors in Figure 3 gives dimming control of LED current from 0mA to 20mA.

22µH

L1

D1

C3

1µF

R1

910k

R2

27k

R3

C2

1µF

C4

10nF

C1

10µF

PGND

VIN

ENA

Comp

SW

OVP

FB

GND

PWM

PAM2841

PGND

VIN

ENA

Comp

SW

OVP

FB

GND

PAM2841

VIN

VIN

ENA

PWM

L1

22µH

D1

C3

1µF

R1

910k

R2

27k

C1

10µF

C2

1µF

R3

C4

10nF

Q1