BAT54 View Datasheet(PDF) - Samhop Mircroelectronics
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SAMHOP Microelectronics Corp.
1.2MHz STEP-UP CONVERTER
GENERAL DESCRIPTION
The SM8237 is a step-up DC/DC converter
specifically designed to drive white LEDs with a
constant current. The device can drive two, three
or four 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
SM8237 switches at 1.2 MHz, allowing the use of
tiny external components. The output capacitor can
be as small as 0.22μF, saving space and cost
versus alternative solutions. A low 95mV feedback
voltage minimizes power loss in the current setting
resistor for better efficiency.
FEATURES
* Inherently matched LED current
* High efficiency : 84% typical
* Drives up to four LEDs from a 2.8V supply
* Drives up to six LEDs from a 5V supply
* 36V rugged bipolar switch
* Fast 1.2MHz switching frequency
* Uses tiny 1 mm tall inductors
* Requires only 0.22μF output capacitor
* Low profile TSOT package
TYPICAL APPLICATION
Vin
3.3 V
OFF ON
L1
22 uH
D1
C1
4.7 uf
5
1
Vin
SW
4 SD SM8237 FB 3
GND
2
R1
51 K
Vout
5V / 100 mA
C2
1 uf
C1 , C2 : X7R Dielectric
D1 : Frontier electronics SS14
R2
L1 : Frontier electronics CSS0218P-22ON-LFR
1K
OUTPUT VOLTAGE vs. LOAD CURRENT
5.20
5.15
5.10
5.05
5.00
Vin = 3.3V
4.95
4.90
4.85
4.80
0 10 20 30 40 50 60 70 80 90 100 105
OUTOPuUtpTutCCUurRreRnEt (NmTA)(mA)
100
95
90
85
80
75
70
65
60
55
50
0
EFFICIENCY vs. LOAD CURRENT
Vin = 3.3V
Vout = 5V
10 20 30 40 50 60 70 80 90 100 105
OUTPOUuTtpuCt CUuRrrRenINt (mTA()mA)
Page 1
V.1.3 Aug 28,2007
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