SP6699 datasheet(9/12 Pages) EXAR

9 / 12 page

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Rev. 2.1.0

PWM signal when it is applied on the CTRL pin.

The typical frequency of this PWM signal is

200Hz to 1KHz. Please refer to figure 21.

Fig. 21: Dimming Control using a PWM Signal

on CTRL Pin

Secondly, adding a constant DC voltage

through a resistor divider to CTRL pin can

control the dimming. The FB voltage is

indirectly adjusted when the CTRL pin voltage

is between 50mV to 1.8V, which can be used

as dimming control. Please refer to figure 22.

Fig. 22: Dimming COntrol using a DC Voltage

on CTRL Pin

Thirdly, using a filtered PWM signal added to

the CTRL pin can achieve dimming control.

The filtered PWM signal can be considered as

an adjustable DC voltage. It will change the FB

voltage

indirectly

and

achieve

dimming

control. The circuit is shown in Figure 23.

Fig. 23: Dimming Copntrol using a Filtered PWM Signal

on CTRL Pin

Changing the effective feedback voltage

There are three methods to change the

effective feedback voltage.

First, adding a constant DC voltage through a

resistor divider to FB pin can control the

dimming. Changing the DC voltage or resistor

between the FB Pin and the DC voltage can

get appropriate luminous intensity. Comparing

with all kinds of PWM signal control, this

method features a stable output voltage and

LEDs current. Please refer to figure 24.

Fig. 24: Dimming Control using a DC Voltage

Second, using a filtered PWM signal can do it.

The filtered PWM signal can be considered as a

varying and adjustable DC voltage.

Fig. 25: Dimming Control using a Filtered PWM Voltage

Third, using a logic signal to change the

feedback voltage. For example, the FB pin is

connected to the GND through a MOSFET and

a resistor. And this MOSFET is controlled by a

logic signal. The luminous intensity of LEDs

will be changed when the MOSFET turns on or

off.

Fig. 26: Dimming Control using Logic Signal

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