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PDF RT9288A Data sheet ( Hoja de datos )
| Número de pieza | RT9288A | |
| Descripción | PWM Step-Up DC/DC Controller | |
| Fabricantes | Richtek Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT9288A (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
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RT9288A
PWM Step-Up DC/DC Controller for White-LED Driver
General Description
The RT9288A is a wide input operating voltage range step-
up controller. High voltage output and large output current
are feasible by using an external N-MOSFET. The RT9288A
input operating range is from 3V to 13.5V. Besides, it
could support up to 60V output at 12V input.
The RT9288A is an optimized design for WLED driver
applications. Adjusting the output current of the RT9288A
changes the brightness of the WLEDs. Chip Enable pin
can be used as a digital input allowing WLED brightness
control with a logic-level PWM signal.
Ordering Information
RT9288A
Package Type
E : SOT-23-6
Note :
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Features
z VIN Operating Range : 3V to 13.5V
z Fixed PWM Frequency : 1MHz
z 200Hz to 200kHz PWM Dimming Frequency
z Flexible PWM/Analog Dimming Control
z Voltage Mode with External Compensation
z Soft Start Function
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z TFT LCD Panels
z LED Backlighting
Pin Configurations
(TOP VIEW)
EXT GND COMP
654
23
VDD EN FB
SOT-23-6
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Functional Pin Description
Pin No. Pin Name
Pin Function
1 VDD
Supply Input Voltage Pin. Bypass an 1uF capacitor to GND to reduce the input noise.
2 EN
Chip Enable (Active High).
3 FB
4 COMP
5 GND
6 EXT
Feedback to Error Amplifier Input.
Output of Error Amplifier. Connect a capacitor between the COMP pin and GND for
compensation. While shutdown, this pin is pulled down by an internal resistor.
Ground Pin.
Output for External Transistor.
DS9288A-02 April 2011
www.richtek.com
1
1 page  
RT9288A
Parameter
Symbol
Test Conditions
Output driver
On Resistance (P-MOSFET)
RDS(ON)_P
On Resistance (N-MOSFET)
RDS(ON)_N
Output rising/falling time (Note 5)
Logic
CL = 1000pF, VFB = Low
EN Pin Low Voltage
EN Pin High Voltage
VIL
VIH
Min Typ Max Unit
-- 30 60 Ω
-- 20 40 Ω
-- 100 -- ns
-- -- 0.5 V
1.8
--
VDD
V
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in the natural convection at TA = 25°C on a low effective thermal conductivity test board of
JEDEC 51-3 thermal measurement standard.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. Guarantee by design.
DS9288A-02 April 2011
www.richtek.com
5
5 Page 
RT9288A
Input Current
ΔIL
Inductor Current
ΔVOUT1
Output Current
Time
(1-D)TS
Output Ripple
Voltage (ac)
Time
Figure 5. The Output Ripple Voltage without the
Contribution of ESR
Main Switch Selection
The RT9288A uses an N-MOSFET as the main switch to
achieve power conversion. The main switch stays in two
states in the operation, one is the on state and the other
is the off state. The potential of switching point, LX, is 0V
in the on state. Nevertheless, the potential of LX rises to
output voltage plus the forward voltage of D1 in the off
state, this potential is the highest voltage in the Boost
converter. Thus, the absolute VDS rating of the main switch
must be greater than this voltage to prevent main switch
damage in the off state or reliability problem. Another key
parameter of main switch is the maximum continuous
drain current. For a safety design, it is important to choose
a maximum continuous drain current at two times the
maximum input current. Energy saving is the trend in
recent years. Therefore, design a high efficiency system
is the important course. Conduction loss and switching
loss play important roles for the efficiency in heavy load
and light load respectively. Main switch with a small on
resistance leads to lower conduction loss, however, it also
means a greater gate capacitance. Great gate capacitance
prolongs rising and falling transition in LX, t1 and t2. IL and
VLX produce the main switching loss during t1 and t2. Thus,
choose a main switch with proper gate capacitance could
reduce switching loss.
VIN
CIN
L1 LX D1
IL
VDD
EXT
M1
VOUT
COUT
RT9288A
FB
RF1
RF2
VEXT
VLX
t1
IL
VIN
t2
ΔIL
VTH
Time
VOUT + VD1
Time
IOUT
Time
Figure 6. The Waveforms of EXT, LX and Inductor Current
Related to the Switching Loss
Loop Compensation
It is easy to compensate the loop stability for the
RT9288A's application in LED driving. Compensation
network only contains a capacitor between COMP pin and
GND as shown in figure 1. The best criterion to optimize
the loop compensation is by inspecting the transient
response and adjusting the compensation network.
Layout Consideration
The PCB layout is a very important issue for switching
converter circuits design. There are some recommended
layout guidelines that are shown as follows :
` The power components M1, L1, D1, CIN and COUT should
be placed as close to the IC as possible to reduce the
ac current loop. The connections between power
components must be short and wide as possible due to
large current stream flowing through these traces during
operation.
` The function of C1 is to regulate VDD. Place C1 close to
pin 1 is necessary.
DS9288A-02 April 2011
www.richtek.com
11
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| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet RT9288A.PDF ] | |
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