TK11850L
WHITE LED DRIVER
FEATURES
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Very High Speed Adjustable OSC (Max 800 kHz)
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Very Wide Operating Voltage Range (2.3 V to 10 V)
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Low Loss Detector (Low Reference Voltage:
n
n
n
n
n
n
V
REF
= 0.5 V)
Operates with Toko D31FU Miniature Coil (Current
Limited by Input Current Sensor)
Internal Switching Transistor
Internal Diode
Active High On / Off Control
Available Intensity Control Using EN Pin with PWM
Signal
Very Small SOT23L-8 Surface Mount Package
APPLICATIONS
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LED Backlighting and Frontlighting
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LED Flashlights
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Step-up DC-DC Converters
voltage increase or the inrush current as start-up) that flows
through the coil. The ON /OFF control is built-in and the
circuit current can be decreased when the EN pin is low
(standby mode). The white LEDs can be dimmed by
applying a PWM signal to the EN (ON/OFF control) pin. With
this method, the white LED brightness is still controlled by
constant current resulting in constant chromaticity.
The TK11850L is available in the SOT23L-8 surface mount
package.
DESCRIPTION
The TK11850L is a pulse skipping step-up DC-DC converter
IC designed for White LED driver applications with the
following built in: a very high current switching transistor
(400 mA peak), an inductor current limit detector, low
voltage reference (Vref = 0.5 V), high speed oscillator, an
error comparator, a rectifier diode (for small power output)
and an ON/OFF control. The IC works with a very wide
operating supply range (2.3 V to 10 V) and the adjustable
output voltage can be set as high as 20 V. The device is in
the ON state when the EN pin is pulled to a high level. Using
the very small TK11850L and a few external components,
battery powered systems with LCD displays such as digital
cameras and cellular phones can be effectively backlit with
white LEDs. The white LEDs are connected in series and
driven at a constant current resulting in uniform brightness
and high efficiency. This IC has an oscillator, which allows
the designer to set the operating frequency by an external
capacitor with the output controlled by pulse skipping. The
reference voltage is a very low 0.5 V, achieving high
efficiency operation with the constant current output. A
small coil can be used because the inductor current limit
detector circuit limits the peak current (caused by an input
TK11850
VIN
IS
EXT
VOUT
8
EN
7
CX
GND
VFB
BLOCK DIAGRAM
0.1 V
VIN
IS COMP
+
-
BAND GAP REFERENCE
8 EN
OSC
0.86 V
IS
CX
0.3 V
7 CX
CLK
CLK
ORDERING INFORMATION
TK11850L
Tape/Reel Code
EXT
S
Q
VOUT
VREF
0.525 V
GND
ERROR
COMP
R
+
-
VFB
TAPE/REEL CODE
TL: Tape Left
May 2001 TOKO, Inc.
Page 1
TOKO [ TOKO, INC ]
