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Step-Up Converter. AF5121 Datasheet

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Step-Up Converter. AF5121 Datasheet






AF5121 Converter. Datasheet pdf. Equivalent




AF5121 Converter. Datasheet pdf. Equivalent





Part

AF5121

Description

Fixed Frequency White LED Step-Up Converter



Feature


AF5121 Fixed Frequency White LED Step-Up Converter Features  Inherently Mat ched LED Current  High Efficiency:82 %  Drives Up to Six LEDs from 2.2V S upply  20V Over Voltage Protection  Fast 1.4MHz Switching Frequency  Requires Only 1μF Output Capacitors SOT-23-6 Package Applications  C ommunication equipment  White LED Ba cklight Display for PDA  Pocket PC .
Manufacture

AFSEMI

Datasheet
Download AF5121 Datasheet


AFSEMI AF5121

AF5121;  Handheld Devices  Cellular Phones  White LED display backlighting Ge neral Description The AF5121 is a step- up DC/DC converter specifically designe d to drive up to 6 series white LEDs wi th constant current. Series connection of the LEDs provides identical LED curr ents resulting in uniform brightness an d eliminates the need for ballast resis tors. The AF5121 switche.


AFSEMI AF5121

s at 1.4MHz, allowing the use of tiny ex ternal components. A low 0.25V feedbac k voltage minimizes power loss in the c urrent setting resistor for high effici ency. The OVP pin monitors the output v oltage and turns off the converter wh .


AFSEMI AF5121

.

Part

AF5121

Description

Fixed Frequency White LED Step-Up Converter



Feature


AF5121 Fixed Frequency White LED Step-Up Converter Features  Inherently Mat ched LED Current  High Efficiency:82 %  Drives Up to Six LEDs from 2.2V S upply  20V Over Voltage Protection  Fast 1.4MHz Switching Frequency  Requires Only 1μF Output Capacitors SOT-23-6 Package Applications  C ommunication equipment  White LED Ba cklight Display for PDA  Pocket PC .
Manufacture

AFSEMI

Datasheet
Download AF5121 Datasheet




 AF5121
AF5121
Fixed Frequency White LED Step-Up Converter
Features
Inherently Matched LED Current
High Efficiency:82%
Drives Up to Six LEDs from 2.2V
Supply
20V Over Voltage Protection
Fast 1.4MHz Switching Frequency
Requires Only 1μF Output Capacitors
SOT-23-6 Package
Applications
Communication equipment
White LED Backlight Display for PDA
Pocket PC
Handheld Devices
Cellular Phones
White LED display backlighting
General Description
The AF5121 is a step-up DC/DC converter
specifically designed to drive up to 6 series white
LEDs with constant current. Series connection of
the LEDs provides identical LED currents
resulting in uniform brightness and eliminates the
need for ballast resistors. The AF5121 switches
at 1.4MHz, allowing the use of tiny external
components. A low 0.25V feedback voltage
minimizes power loss in the current setting
resistor for high efficiency. The OVP pin monitors
the output voltage and turns off the converter
whenever the LEDs are open.
The AF5121 is available in low profile SOT-23-6
package.
Block Diagram
Analog Future Ver1.0
1 www.afsemi.com




 AF5121
Pin Assignment
AF5121
Fixed Frequency White LED Step-Up Converter
SOT23-6(Top View)
SW 1
6 VIN
GND 2
5 OVP
FB 3
4 SHDN
Order Information
AF5121①②
Designator
Symbol
E
R
G
Description
Package:SOT23-6
RoHS / Pb Free
Halogen Free
Typical Application Circuit
Analog Future Ver1.0
2 www.afsemi.com




 AF5121
AF5121
Fixed Frequency White LED Step-Up Converter
Absolute Maximum Ratings
Input Voltage ..............................................20V
FB Voltage ............................................0.25V
OVP Voltage...................................................20V
SW Frequence..........................................1.4Mhz
SHDN Voltage ........................................6V
Storage Temperature .......................-65 to 150
Continuous Power Dissipation……...600mW
Operating Junction Temperature…….-20 to 85
Note: These are stress ratings only. Stresses exceeding the range specified under “Absolute Maximum
Ratingsmay cause substantial damage to the device. Functional operation of this device at other
conditions beyond those listed in the specification is not implied and prolonged exposure to extreme
conditions may affect device reliability.
Electrical Characteristics
Parameter
Symbol
Input Voltage
Vin
Feedback Voltage
VFB
Switching Frequency
FSW
SHDN Voltage High
VH
SHDN Voltage Low
VL
OVP Voltage
Vovp
FB Pin Bias Current
Supply Current
Shutdown Current
Maximum Duty Cycle
Switch Current Limit
Switch Leakage Current
Switch Vcesat
IFB
IIN
IOFF
DMAX
ILIM
ISW
VSAT
Test Conditions
--
Iout=20 mA,6LED
Iout=20mA
--
--
--
IOUT=20mA
IOUT=0mA
VSHDN=0V
VSW=5V
ISW=250mA
VEN=3.8VVIN=3.8VTa=25
Min Typ Max Unit
2.2
--
20.0
V
210 250 275 mV,
1.1 1.4 1.5 MHz
1.2 --
-- V
-- -- 0.8 V
-- 20 -- V
50 100 200 nA
-- 3.0 5.0 mA
-- 0.5 1.0 uA
-- 85 90 %
600 700 750 mA
-- 0.1 1 A
-- 300 -- mV
Function Description
The AF5121 uses a constant frequency control scheme to provide excellent line and load regulation. Operation can be
best understood by referring to the block diagram. At the start of each oscillator cycle, the SR latch is set, which turns
on the power switch M1. An artificial ramp is generated to the positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the SR latch is reset turning off the power switch. The level at the
negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the
feedback voltage and the reference voltage of 0.254V. In this manner, the error amplifier sets the correct peak current
level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output, if
it decreases, less current is delivered.
Analog Future Ver1.0
3 www.afsemi.com



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