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  Richtek Technology Electronic Components Datasheet  

RT9271 Datasheet

White LED Step-Up Converter

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RT9271
White LED Step-Up Converter in Tiny Package
General Description
The RT9271 is a step-up DC/DC converter specifically
designed to drive white LEDs with a constant current.
The device can drive one to three LEDs in series from a
Li-Ion cell. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness and
eliminating the need for ballast resistors. The RT9271
switches at 1.1 MHz, allowing the use of tiny external
components. The input and output capacitor can be as
small as 1uF, saving space and cost versus alternative
solutions. A low 0.25V feedback voltage minimizes power
loss in the current setting resistor for better efficiency.
The RT9271 is available in low profile SOT-26 package.
Ordering Information
RT9271
Package Type
B : SOT-25
E : SOT-26
Operating Temperature Range
C : Commercial Standard
P : Pb Free with Commercial Standard
Marking Information
For marking information, contact our sales representative
directly or through a RichTek distributor located in your
area, otherwise visit our website for detail.
Features
Inherently Matched LED Current
High Efficiency: 85% Typical
Drives Up to Three LEDs from 2.8V Supply
20V Internal Switch
Fast 1.1 MHz Switching Frequency
Uses Tiny 1 mm Height Inductors
Requires Only 1uF Output Capacitor
Low Profile SOT-26 Package
Optional 15V Over Voltage Protection
Applications
Mobile Phone
Digital Still Camera
PDAs, Handheld Computers
MP3 Players
GPS Receivers
Pin Configurations
(TOP VIEW)
LX 1
GND 2
FB 3
5 VCC
4 CE
LX 1 6 VCC
GND 2 5 OVP
FB 3 4 CE
SOT-25
SOT-26
Functional Pin Description
Pin No. Pin Name Pin Function
XB XE
11
LX Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI.
22
GND Ground Pin. Connect directly to local ground plane.
33
44
5
56
FB
CE
OVP
VCC
Feedback Pin. Reference voltage is 0.25V. Connect cathode of lowest LED and resistor
here. Calculate resistor value according to the formula: RFB = 0.25/ILED
Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.4V or less to disable
device.
Over Voltage Protection Pin. Voltage sensing input to trigger the function of over voltage
protection, the trip point is 15.5V. Leave it unconnected to disable this function.
Input Voltage Pin. Must be locally bypass with 1uF capacitor to GND.
DS9271-07 April 2004
www.richtek.com
1


  Richtek Technology Electronic Components Datasheet  

RT9271 Datasheet

White LED Step-Up Converter

No Preview Available !

RT9271
Typical AppIication Circuit
VIN
2.4 to 3.2V
C1
1uF
Dimming
Control
LX
10uH
D1
SS0520
VCC
CE
LX
OVP
GND
FB
C3 D2
1uF
R2
12Ω
Figure 1. RT9271 Drivers 1 WLED Application Circuit
VIN
2.4 to 5V
C1
1uF
Dimming
Control
LX
10uH
D1
SS0520
VCC
CE
LX
OVP
GND
FB
D2
C3
1uF
D3
R2
12Ω
Figure 2. RT9271 Drivers 2 Series WLEDs Application Circuit
VIN
2.4 to 6V
C1
1uF
Dimming
Control
LX
10uH
D1
SS0520
VCC
CE
LX
OVP
GND
FB
C3
1uF
R2
12Ω
D2
D3
D4
Figure 3. RT9271 Drivers 3 Series WLEDs Application Circuit
Note : 1. D1 is Schottky diode (SS0520).
2. D2 ~ D4 are the WLED (HT-S91CW-DT) of HARVATEK.
3. LX is the SH4018 series of ABC TAIWAN ELECTRONICS CORP.
www.richtek.com
2
DS9271-07 April 2004


Part Number RT9271
Description White LED Step-Up Converter
Maker Richtek
PDF Download

RT9271 Datasheet PDF






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