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TK11850L Datasheet Preview

TK11850L Datasheet

WHITE LED DRIVER

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TK11850L
WHITE LED DRIVER
FEATURES
n Very High Speed Adjustable OSC (Max 800 kHz)
n Very Wide Operating Voltage Range (2.3 V to 10 V)
n Low Loss Detector (Low Reference Voltage:
VREF = 0.5 V)
n Operates with Toko D31FU Miniature Coil (Current
Limited by Input Current Sensor)
n Internal Switching Transistor
n Internal Diode
n Active High On / Off Control
n Available Intensity Control Using EN Pin with PWM
Signal
n Very Small 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
ORDERING INFORMATION
TK11850L
Tape/Reel Code
TAPE/REEL CODE
TL: Tape Left
APPLICATIONS
n LED Backlighting and Frontlighting
n LED Flashlights
n 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.
TK11850
VIN
IS
EXT
VOUT
8 EN
7 CX
GND
VFB
BLOCK DIAGRAM
0.1 V
IS COMP
VIN +
-
IS
BAND GAP REFERENCE
OSC
0.86 V
CX 0.3 V
CLK
CLK
8 EN
7 CX
EXT
VOUT
S
QR
ERROR
COMP
+
-
VREF
0.525 V
GND
VFB
May 2001 TOKO, Inc.
Page 1




TOKO

TK11850L Datasheet Preview

TK11850L Datasheet

WHITE LED DRIVER

No Preview Available !

TK11850L
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ........................................................ 20 V
Switching Voltage .................................................... 20 V
Operating Voltage Range ............................... 2.3 to 10 V
Power Dissipation (Note 1) ................................. 400 mW
Storage Temperature Range ..................... -55 to +150 °C
Operating Temperature Range ..................... -30 to +85 °C
Switching Peak Current ....................................... 400 mA
Diode Current ........................................................ 10 mA
Maximum Frequency ...................................... ~ 800 kHz
TK11850 ELECTRICAL CHARACTERISTICS
Test Conditions: VIN = 3 V, VIS =VEN = VIN, VEXT = Open, VFB = GND, CX = 100 pF, TA = 25 °C, unless otherwise specified.
SYMBOL
PARAMETER
TEST CONDITIONS
MIN
OSCILLATOR SECTION (CX PIN)
I C Charging Current
CHG
X
IDIS CX Discharging Current
IDIS / ICHG
Charge and Discharge
Current Ratio
V = 0.1 V
CX
VCX = 1.0 V
16
35
VCX (HIGH) CX Threshold Voltage +
VCX at ICHG = 0mA
VCX (LOW) CX Threshold Voltage -
VCX at IDIS = 0mA
VOSC
CX Oscillation Voltage
(Vth +) - (Vth -)
CURRENT LIMITING COMPARATOR SECTION (IS PIN)
VLIMIT
Current Limit Sense
Voltage
VLIMIT = VIN - VIS
810
260
520
72
IIsIn IS Pin Bias Current
VIN = VIS = 3 V
OUTPUT SWITCH SECTION (EXT PIN)
5
VSW, Sat
Output Transistor
Saturation Voltage
VCX = 0 V, ISW = 200 mA
I
SW, Off
Output Transistor Off
Leakage Current
V = 1 V, V = 20 V
FB EXT
FEEDBACK COMPARATOR SECTION (VFB PIN)
VREF Reference Voltage
0.505
IFBIn
VFB Pin Output Current
VFB = 0.4 V
-2
Note 1: Power dissipation is 400 mW when mounted. Derate at 3.2 mW / °C for operation above 25 °C.
TYP
22
49
2.2
860
300
560
77
10
0.2
0.01
0.525
-0.3
MAX UNITS
30 mA
65 mA
910 mV
340 mV
600 mV
82 mV
15 mA
0.4 V
2 mA
0.545
V
mA
Page 2
May 2001 TOKO, Inc.


Part Number TK11850L
Description WHITE LED DRIVER
Maker TOKO
Total Page 14 Pages
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