YB1315 Datasheet, PDF (7/10 Pages) YOBON TECHNOLOGIES,INC. – High Efficiency Charge Pump White LED Driver

Preliminary YB1315
High Efficiency Charge Pump White LED Driver
Application Information
Soft-Start Circuitry
The YB1315 includes soft-start circuitry to
limit inrush current at turn-on. Once the
input voltage is applied, the output
capacitor is charged directly from the input
with a ramped current source (with no
charge-pump action) until the output
voltage approaches the input voltage.
Once this occurs, the charge pump
determines if 1x or 1.5x mode is required.
In the case of 1x mode, the soft-start is
terminated and normal operation begins. In
the case of 1.5x mode, soft-start operated
until the lowest of LED1-LED5 reaches
regulation.
ENABLE (EN1, EN2)
The enable pins EN1 and EN2 are used to
enable or shutdown the device. The
YB1315 is enabled if one of the enable pins
is pulled higher than the enable trip point of
1.2V. The device starts up by going
through the soft start routine as described
above. Pulling both pins to GND, after a
delay, forces the device into to shutdown
mode. In shutdown, the charge pump,
current sources, voltage reference,
oscillator, and all other functions are turned
off and the supply current is reduced to
0.1μA.
Methods for Dimming Control
YB1315 offers flexible ways for dimming
control.
1. EN1 and EN2 can be used for dimming.
The logic levels at EN1 and EN2 set the
minimum voltage at the current mirrors
and the voltage at the ISET pin to GND.
This sets the current at the LEDs to be
either the full current or a fraction of the
full current. See Table 4 for further
details. The maximum current through
the LEDs is set by a resistor connected
between ISET and GND described
later.
Table 4. Enable Levels
Enable Level
EN2 EN1
MODE
LED
Current
0
0
Shutdown
0
0
1
V_ISET=200mV
1/3
1
0
V_ISET=400mV
2/3
1
1
V_ISET=600mV
Full
2. EN1 and EN2 can also be used for
PWM dimming. The LED brightness
level is directly dependent on the duty
cycle of the PWM signal and the
configuration. The PWM signal can
either be applied to EN1 or EN2, or both
tied together, and the PWM signal can
be applied to both pins. Depending on
the configuration, the current during
PWM dimming is switched between
0mA and its maximum (EN1 and EN2
connected to the PWM signal) or
between 0mA and 1/3 of the full LED
current if EN2= 0 and EN1 is toggled.
When EN1 = 0 and EN2 is toggled, the
output current can be changed between
0mA and 2/3 of the full range.
LED Current Setting
The current of white LED connected to
YB1315 can be set by R_SET. Every current
flow through the white LED is 250 times
YB1315 Rev.0.1
www.yobon.com.tw
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