PAM2841 Datasheet, PDF (11/16 Pages) Power Analog Micoelectronics – 1.5ASW Current, 40V Precision WLED Driver

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PAM2841
Application Information (cont.)
3). Using a DC Voltage
For some applications, a simple and direct way to control brightness is use 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.
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.
PAM2841
Document number: DSxxxxx Rev. 1 - 5
Figure 4
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