RT9363A RICHTEK [Richtek Technology Corporation], RT9363A Datasheet - Page 9

• Manufacturer Part Number: RT9363A
• Description: 3 Channels 90mA x1/x2 Charge Pump White LED Driver
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Application information
The RT9363A uses a fractional switched capacitor charge
pump to power up to three white LEDs with a programmable
current. The part integrates current sources and automatic
mode selection charge pump. It maintains the high
efficiency by utilizing an x1/x2 fractional charge pump and
current sources. The small equivalent x1 mode open loop
resistance and ultra-low dropout voltage of current source
extend the operating time of x1 mode and optimize the
efficiency in white LED applications. The operating voltage
range is from 2.8V to 5.5V. Internal soft start circuitry
effectively reduces the in-rush current while both start-up
and mode transition. The load is disconnected from V
while shutdown and the shutdown current is less than 1uA.
High Efficiency x1/x2 Charge Pump
Before the discussion of efficiency in RT9363A, two things
need to be illustrated. One is the Li-ion battery life time,
the other is the forward voltage of white LED. The Li-ion
battery energy is not linearly proportion to battery voltage.
In the
is arranged from 3.65V to 4.0V. The other voltage range
occupies less than 20% battery energy and is insignificant.
In the backlight application, the forward voltage of white
LEDs most likely falls in 3.2 to 3.5V @I
developing concept of RT9363 is based on the backlight
application with Li-ion battery. RT9363A is very cost-effective
product for white LEDs backlight driving. It extends the
80% battery life by the reduction of open loop resistance
at x1 mode and current source drop out voltage. Figure 7
is the efficiency diagram of RT9363 and 80% battery life is
marked by red rectangle. The RT9363A maximize the
x1 mode operating range in the 80% battery life. Therefore,
the efficiency is not significant different to that without
x1.5 mode charge pump. The peak efficiency of RT9363A
is 93% and the average is 84%. Comparing to the LED
drivers with x1.5 mode, only 1 to 2% efficiency loss by x2
mode. (Assume 5% battery life in charge pump mode and
the efficiency difference of x1.5 and x2 modes is 25%, the
efficiency loss thus is 5%x25% = 1.25%).
DS9363A-03 April 2011
Figure 6, It shows the 80% battery life of Li-ion
LED
= 20mA. The
IN
Protection
The RT9363A includes a soft start circuit to limit the inrush
current at power on and mode transition.
Soft start circuit holds the input current level long enough
for output capacitor C
When the soft start off, the RT9363A won't sink spike
current from V
the output voltage from dangerous high voltage. The OVP
turns off charge pump when the voltage difference between
V
LED Current Setting
In Backlighting part, an internal R
initial current (20mA) of white LED and implements a 4-bit
DAC for brightness control. Users can easily configure the
LED current by a serial pulse. The dimming of white LEDs'
current can be achieved by applying a pulse signal to the
EN pin. There are totally 16 steps of current could be set
by users. An automatic R
this part. RT9363A can automatically select the
or external R
current can be calculated by the following equation.
where V
connected from ISET pin to GND.
I
LED
IN
and V
= 276
SET
OUT
12.1k
30.1k
R
10k
15k
20k
⎛
⎜
⎝
SET
= 1.1V (typ.) and R
R
V
SETs
is over the designed target.
IN
LED Current Setting Table
SET
SET
. An over voltage protection function protect
by the connection of ISET pin. The LED
⎞
⎟
⎠
OUT
reaching a desired voltage level.
SET
selection is implemented in
SET
LED current (m A)
SET
is the external resistor
RT9363A
30.3
25.1
20.2
15.2
10.1
is used to set the
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internal
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