YB1506 Datasheet, PDF (7/10 Pages) YOBON TECHNOLOGIES,INC. – Step-up DC-DC Converter , White LED Driver

YB1506
Step-up DC-DC Converter , White LED Driver
LED Current Control
The LED current is controlled by the
feedback resistor (R1 in Figure 1). The
feedback reference is 400mV. The LED
current is 400mV/R1. In order to have
accurate LED current, precision resistors
are preferred (1% is recommended).
The formula and table for R1 selection are
shown below.
R1 = 95mV/ILED
Table 4. R1 Resistor Value Selection
ILED(mA)
20
15
10
5
1
R1(Ω)
20
26.6
40
80
400
Dimming Control
of brightness control is a variable DC
voltage to adjust the LED current.
The dimming control using a DC
voltage is shown in Figure 5. As the
DC voltage increases, the voltage
drop on R2 increases and the voltage
drop on R1 decreases. Thus, the LED
current decreases. The selection of
R2 and R3 will make the current from
the variable DC source much smaller
than the LED current and much larger
than the FB pin bias current. For VDC
range from 0V to 2V, the selection of
resistors in Figure 5 gives dimming
control of LED current from 0mA to
15mA.
3. Using a Filtered PWM Signal
The filtered PWM signal can be
considered as an adjustable DC
voltage. It can be used to replace the
variable DC voltage source in
dimming control. The circuit is shown
in Figure 7.
There are four different types of dimming
control circuits:
1. Using a PWM Signal to SHDN Pin
With the PWM signal applied to the SHDN
pin, the YB1506 is turned on or off by the
PWM signal. The LEDs operate at either
zero or full current. The average LED
current increases proportionally with the
duty cycle of the PWM signal. A 0% duty
cycle will turn off the YB1506 and
corresponds to zero LED current. A 100%
duty cycle corresponds to full current. The
typical frequency range of the PWM signal
is 1kHz to 10kHz. The magnitude of the
PWM signal should be higher than the
minimum SHDN voltage high.
4. Using a Logic Signal
For applications that need to adjust
the LED current in discrete steps, a
logic signal can be used as shown in
Figure 6. R1 sets the minimum LED
current (when the NMOS is off). RINC
sets how much the LED current
increases when the NMOS is turned
on. The selection of R1 and RINC
follows formula (1) and Table 4.
2. Using a DC Voltage
For some applications, the preferred
YB1506 MRev1.1
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