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PDF RT9271 Data sheet ( Hoja de datos )
| Número de pieza | RT9271 | |
| Descripción | White LED Step-Up Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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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
1 page  
Typical Operating Characteristics
Efficiency vs. VIN (Driving 1 WLED)
92
TA = 25°C
91
90
89
88
87
86 IO = 20mA
85 IO = 15mA
84
83
82
2
2.5 3 3.5
VIN (V)
4
Efficiency vs. VIN (Driving 3 WLEDs)
90
TA = 25°C
89
88
87
86
85 IO = 20mA
84
83 IO = 15mA
82
81
80
23456
VIN (V)
VFB vs. Temperature
260 Driving 3 WLEDs
VIN = 3.6V
255
250
245
240
235
230
0
10 20 30 40 50 60 70
Temperature (°C)
DS9271-07 April 2004
RT9271
Efficiency vs. VIN (Driving 2 WLEDs)
90
89 TA = 25°C
88
87
86 IO = 20mA
85
84
83 IO = 15mA
82
81
80
2
345
VIN (V)
6
Frequency vs. VIN
1.3 Driving 3 WLEDs
TA = 25°C
1.2
1.1
1
0.9
0.8
0.7
23456
VIN (V)
VIN vs. Temperature
3
2.8
2.6
3 WLEDs
2.4
2.2
Minimum Input Voltage vs. Temperature
for Delivering Full Brightness
2
20 30 40 50 60
Temperature (°C)
70
www.richtek.com
5
5 Page 
Outline Dimension
RT9271
D
CB
H
L
b
A
e
A1
Symbol
A
A1
B
b
C
D
e
H
L
Dimensions In Millimeters
Min Max
0.889
1.295
0.000
0.152
1.397
1.803
0.356
0.559
2.591
2.997
2.692
3.099
0.838
1.041
0.080
0.254
0.300
0.610
Dimensions In Inches
Min Max
0.035
0.051
0.000
0.006
0.055
0.071
0.014
0.022
0.102
0.118
0.106
0.122
0.033
0.041
0.003
0.010
0.012
0.024
SOT- 25 Surface Mount Package
DS9271-07 April 2004
www.richtek.com
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet RT9271.PDF ] | |
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