RT9363A RICHTEK [Richtek Technology Corporation], RT9363A Datasheet - Page 10

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

RT9363A
Typical Operation
As shown in the typical application circuit, the power of
the RT9363A is provided from the external adapter or
battery. When EN pin is low, the white LED for backlighting
is turned off and draws a very low current from battery
supply.
When EN pin is high, RT9363A provides a twice mode
load switch (x1) and high efficiency (x2) charge pump device
intended for white LED backlight applications. To maximize
the power conversion efficiency, an internal sensing circuit
monitors the voltage required on each constant sink input
and sets the load switch and charge pump modes based
on the input battery voltage and the current sink input
voltage. RT9363A provides the option to control the
16-steps brightness of white LEDs with a digital pulse signal
applied to EN pin and the detailed timing of pulse dimming
is shown in Figure 5.
Capacitors Selection
To get the better performance of RT9363A, the selection
of peripherally appropriate capacitor and value is very
important. These capacitors determine some parameters
such as input and output ripple, power efficiency, maximum
supply current by charge pump, and start-up time.
To reduce the input and output ripple effectively, the low
ESR ceramic capacitors are recommended. Generally,
to reduce the output ripple, increasing the output
capacitance C
the start-up time of output voltage. For LED driver
applications, the input voltage ripple is more important
than the output ripple. Input ripple is controlled by input
capacitor C
can further reduce the ripple. Practically, the input voltage
ripple depends on the power supply's impedance. Tantalum
capacitors are not recommended for the RT9363A. If
tantalum must capacitors are needed, C
larger than 10μF and 1μF. Because tantalum capacitors'
values are less than normal when using for high frequency
applications. So tantalum capacitor values and ceramic
capacitor values can't be the same. But C
tantalum capacitor, because during the x2 mode charge
pump the V
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10
OUT
IN
, increasing the value of input capacitance
OUT
is negative voltage.
is necessary. However, this will increase
IN
and C
OUT
can't use
FLY
must
The traces running from pins to
flying capacitor should be short
and wide to reduce parasitic
resistance and prevent noise
radiation.
All the traces of LED and VIN running
from chip to LEDs should be wide and
short to reduce the parasitic connection
resistance and shielded, isolated by
ground plane. The Anodes of LEDs
must connect to C
directly.
Figure 7. Efficiency of RT9363A. (I
PCB Board Layout
Figure 6. Li-ion Battery Energy Capacity Versus Battery
Battery Voltage
100
90
80
70
60
50
40
3.65
4.2
4.0
2.6
(V)
C
FLY
50
2.8
IN
LED3
LED2
LED1
, not battery
Figure 8. PCB Layout Guide
CN
CP
Battery Life
3.0
LED Efficiency vs. V
1
2
3
4
5
80%
3.2
Voltage.
The exposed pad, GND
pad should be connected
to a strong ground plane
for heat sinking and noise
prevention.
GND
3.4
V
Output capacitor must be placed close to
the VOUT and connect to GND plane.
IN
(V)
10
3.6
9
8
7
9
DS9363A-03 April 2011
650
LED
EN
ISET
VOUT
VIN
GND
= 60mA, V
3.8
Capacity (mAH)
C
R
OUT
IN
4.0
SET
Input capacitor must
be placed close to
the VIN and connect
to GND plane.
C
4.2
F
IN
= 3.5V)
4.4