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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: 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
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.
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
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
TYP
MAX
UNITS
OSCILLATOR SECTION (CX PIN) ICHG IDIS IDIS / ICHG VCX (HIGH) VCX (LOW) VOSC CX Charging Current CX Discharging Current Charge and Discharge Current Ratio CX Threshold Voltage + CX Threshold Voltage CX Oscillation Voltage VCX at ICHG = 0mA VCX at IDIS = 0mA (Vth +) - (Vth -) 810 260 520 VCX = 0.1 V VCX = 1.0 V 16 35 22 49 2.2 860 300 560 910 340 600 mV mV mV 30 65 mA mA
CURRENT LIMITING COMPARATOR SECTION (IS PIN) VLIMIT IIsIn Current Limit Sense Voltage IS Pin Bias Current VLIMIT = VIN - VIS VIN = VIS = 3 V 72 5 77 10 82 15 mV mA
OUTPUT SWITCH SECTION (EXT PIN) VSW, Sat ISW, Off Output Transistor Saturation Voltage Output Transistor Off Leakage Current VCX = 0 V, ISW = 200 mA VFB = 1 V, VEXT = 20 V 0.2 0.01 0.4 2 V mA
FEEDBACK COMPARATOR SECTION (VFB PIN) VREF IFBIn Reference Voltage VFB Pin Output Current VFB = 0.4 V 0.505 -2 0.525 -0.3 0.545 V mA
Note 1: Power dissipation is 400 mW when mounted. Derate at 3.2 mW / C for operation above 25 C.
Page 2
May 2001 TOKO, Inc.
TK11850L
TK11850 ELECTRICAL CHARACTERISTICS (CONT)
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
TYP
MAX
UNITS
SHUTDOWN SECTION (EN PIN) VEN (HIGH) VEN (LOW) IENIn EN Threshold Voltage + EN Threshold Voltage EN Pin Bias Current On Mode Shutdown Mode VIN = VEN = 3 V 0.6 2 5 8 2 V V mA
DIODE SECTION (EXT PIN - VOUT PIN) VF Forward Voltage ID = 10 mA 0.75 V
VIN SECTION (VIN PIN) VIN (LOW) VIN (HIGH) ICC (Off) ICC (On) Low Voltage Stop High Voltage Output Stop Shutdown Supply Current Quiescent Supply Current VEN = 0 v VFB = 1 V 1 1.7 11 2.0 12.5 0.01 1.5 2.3 14 1 2 V V mA mA
Reference Value Efficiency ILOAD = 20 mA, VOUT = 16.5 V, VIN = 3.6 V (Note 2) 78 %
Note 2: This value is different depending on the components used, circuit conditions, etc. Thus, this is reference data only. Refer to Reference data test circuit.
May 2001 TOKO, Inc.
Page 3
TK11850L
TEST CIRCUIT
ICC VIN VIN VIN V 10 F EN
8
IEN VEN V IDIS ICHG VCX 100 pF V
IIS IS VIS V IEXT EXT VEXT GND CX
7
V
IVOUT
VOUT VVOUT
VFB VFB V
IFB
V
REFERENCE DATA TEST CIRCUIT
ICC VIN 3.6 V V RSC 0.22 CIN 47 VIN
8
L 15
ILOAD D 2200p VOUT 20 mA
COUT 47 IS VOUT EXT 620k
EN
TK11850L
VFB
L = 15 mH D52LC (A914BYW - 150M) Toko D - SB07 - 03C Sanyo
7
CX CX 56 pF
GND
20k
Page 4
May 2001 TOKO, Inc.
TK11850L
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25 C, unless otherwise specified.
OSC PERIOD vs. CX CAPACITANCE 12 11 10 9 8 7 6 5 4 3 2 1 0 300
MAXIMUM DUTY CYCLE (%)
OSC FREQUENCY (kHz)
OSC FREQUENCY vs. TEMPERATURE
VIN = 3 V VIN = 5 V VIN = 10 V
MAXIMUM DUTY CYCLE vs. OSC FREQUENCY 80
VIN = 3 V VIS = VEN = VIN VFB = 0 V
OSC PERIOD (S)
VIN = 3 V VIS = VEN = VIN
280 260 240 220 200 180
VIS = VEN =VIN CX = 100 pF
75
70
0
100 200 CX CAPACITANCE (pF)
300
-30
-10 10 30 50 70 TEMPERATURE (C)
90
65 10 100 OSC FREQUENCY (kHz) 1000
SWITCHING CURRENT vs. SWITCH SATURATION VOLTAGE 500
INDUCTOR CURRENT-LIMIT SENSE VOLTAGE vs. SUPPLY VOLTAGE
-20 C 25 C 85 C Vlimit = VIS - VIN VEN = VIN
IS INPUT BIAS CURRENT vs. IS VOLTAGE
IS INPUT BIAS CURRENT (A)
SWITCHING CURRENT (mA)
400
-20 C 25 C
INDUCTOR CURRENT-LIMIT SENSE VOLTAGE (mV)
100 90 80 70 60 50 40 30 20 10 0
100 90 80 70 60 50 40 30 20 10 0 0 2
-20 C 25 C 85 C
300 200 100 0
85 C
VIN = 3 V VIS = VEN = VIN VFB = 0 V VCX = 0 V
VIN = VEN = VIS VFB = 1 V
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 SWITCH SATURATION VOLTAGE (V)
2
4 6 8 10 SUPPLY VOLTAGE (V)
12
4
6 8 10 12 14 16 18 20 IS VOLTAGE (V)
REFERENCE VOLTAGE vs. SUPPLY VOLTAGE 530 REFERENCE VOLTAGE (mV)
REFERENCE VOLTAGE (mV)
REFERENCE VOLTAGE vs. TEMPERATURE 530 528 526 524 522 520 518 516 -30 -10 10 30 50 70 TEMPERATURE (C) 90
VIN = 3 V VIS = VEN = VIN
SUPPLY CURRENT vs. EN VOLTAGE 10 9
-20 C 25 C 85 C
SUPPLY CURRENT (mA)
528 526 524 522 520 518 516 0 2 4 6 8 SUPPLY VOLTAGE (V) 10
VIS = VEN = VIN
8 7 6 5 4 3 2 1 0
VIN = 3 V VIS = VIN VFB = 0 V CX = 100 pF
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 EN VOLTAGE (V)
May 2001 TOKO, Inc.
Page 5
TK11850L
TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)
TA = 25 C, unless otherwise specified.
SUPPLY CURRENT vs. EN INPUT BIAS CURRENT
EN INPUT BIAS CURRENT (A)
EN INPUT BIAS CURRENT vs. EN VOLTAGE 100 90 80 70 60 50 40 30 20 10 0 0 2 4
VIN = 3 V VIS = VIN -20 C 25 C 85 C
10 9 SUPPLY CURRENT (mA) 8 7 6 5 4 3 2 1 0
VIN = 3 V VIS = VIN VFB = 0 V CX = 100 pF -20 C 25 C 85 C
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 EN INPUT BIAS CURRENT (A)
6 8 10 12 14 16 18 20 EN VOLTAGE (V)
DIODE CURRENT vs. DIODE FORWARD VOLTAGE 10 8 6 4 2 0
SUPPLY CURRENT vs. SUPPLY VOLTAGE 2 1.8
SUPPLY CURRENT (mA)
DIODE CURRENT (mA)
VIS = VEN = VIN
1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0
VIS = VEN = VIN VFB = 1 V CX = 100 pF -20 C 25 C 85 C
300 400 500 600 700 800 DIODE FORWARD VOLTAGE (mV)
0
1
23456789 SUPPLY VOLTAGE (V)
10
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(SHUTDOWN MODE)
10 9
SUPPLY CURRENT (A)
-20 C 25 C 85 C VIS = VIN VEN = 0.6 V
8 7 6 5 4 3 2 1 0 0
2 4 6 8 10 12 14 16 18 20 SUPPLY VOLTAGE (V)
Page 6
May 2001 TOKO, Inc.
TK11850L
APPLICATION CIRCUIT (2 LEDs in Series)
VIN CIN 4.7 F GND VIN 0.1 V IS COMP EN BAND GAP REFERENCE 8 ON/OFF
+
RSC 0.39 IS
OSC 0.86 V CX 0.3 V 7 CX
CLK L 33 uH D31FU TOKO CLK CX 100 pF
EXT
GND
* Input Voltage: 2.7 V * LED Current : 20 mA * On/Off: Pin Number 8 (EN Pin)
LED Current (ILED) is set by RLED. ILED doesn't depend on VIN because ILED is controlled by the feedback circuit.
SB07-03C SANYO VOUT Q
S
ERROR COMP
VFB
R
+ VREF 0.525 V
RLED 27
COUT 2.2 uF VLED
ILED
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25 C, unless otherwise specified. LED Current and Efficiency Characteristics
VIN (V) 2.7 3.0 3.5 4.5 IIN (mA) 71.3 62.9 52.8 39.9 VLED (V) 7.01 7.01 7.02 7.02 ILED (mA) 18.81 18.85 18.95 19.10 EF LED (%) 68.6
L: D31FU, 33 mH Toko Part Number: 888FU-330M
EF LED (%) = 100 * VLED * ILED / VIN * IIN
70.0 71.9 74.8
EF LED vs. VIN 100 80
EF LED (%)
ILED vs. VIN 20 18
ILED (mA)
60 40 20
16 14 12
0
0
2 VIN (V)
4
6
10
0
2 VIN (V)
4
6
May 2001 TOKO, Inc.
Page 7
TK11850L
APPLICATION CIRCUIT (3 LEDs in Series)
VIN CIN 4.7 F GND VIN 0.1 V IS COMP EN BAND GAP REFERENCE 8 ON/OFF
+
RSC 0.27 IS
OSC 0.86 V Cx 0.3 V 7 CX
CLK
* Input Voltage: 2.7 V * LED Current: 20 mA * On/Off: Pin Number 8 (EN Pin)
LED Current (ILED) is set by RLED. ILED doesn't depend on VIN because ILED is controlled by the feedback circuit.
L 22 uH D31FU TOKO
CLK CX 82 pF
EXT SB07-03C SANYO VOUT
GND
S Q
ERROR COMP
VFB
RLED 27
R
+ VREF 0.525 V
COUT 2.2 uF VLED
ILED
TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)
TA = 25 C, unless otherwise specified. LED Current and Efficiency Characteristics
VIN (V) 2.5 2.7 3.0 3.5 4.5 6.0 IIN (mA) 115.9 106.9 95.4 79.1 59.2 42.9 VLED (V) 10.38 10.38 10.38 10.38 10.39 10.39 ILED (mA) 19.41 19.49 19.52 19.52 19.56 19.60 EF LED (%) 69.52 70.09
L: D31FU, 22 mH Toko Part Number: 888FU-220M
EF LED (%) = 100 * VLED * ILED / VIN* IIN
70.83 73.19 76.26 79.04
ILED vs. VIN 20 18
ILED (mA)
EF LED vs. VIN 100 80
EF LED (%)
60 40 20
16 14 12
0
0
2
4 VIN (V)
6
8
10
0
2
4 VIN (V)
6
8
Page 8
May 2001 TOKO, Inc.
TK11850L
APPLICATION CIRCUIT (4 LEDs in Series)
VIN CIN 4.7 F GND VIN 0.1 V IS COMP EN BAND GAP REFERENCE 8 ON/OFF
+
RSC 0.22 IS
OSC 0.86 V CX 0.3 V 7 CX
CLK
* Input Voltage: 2.7 V * LED Current: 20 mA * On/Off: Pin Number 8 (EN Pin)
LED Current (ILED) is set by RLED. ILED doesn't depend on VIN because ILED is controlled by the feedback circuit.
L 15 uH D52LC TOKO
CLK CX 56 pF
EXT SB07-03C SANYO VOUT
GND
S Q
ERROR COMP
VFB
RLED 27
R
+ VREF 0.525 V
COUT 2.2 uF VLED
ILED
TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)
TA = 25 C, unless otherwise specified. LED Current and Efficiency Characteristics
VIN (V) 2.5 2.7 3.0 3.5 4.5 6.0 IIN (mA) 144.4 132.2 117.9 99.0 75.3 55.3 VLED (V) 13.68 13.68 13.68 13.68 13.68 13.68
EF LED vs. VIN 100 80
EF LED (%)
ILED (mA) 19.32 19.30 19.27 19.28 19.35 19.34
EF LED (%) 73.30 73.97
L: D52LC, 15 mH Toko Part Number: A914BYNW - 150M
EF LED (%) = 100 * VLED * ILED / VIN * IIN
74.44 76.07 78.06 79.71
ILED vs. VIN 20 18
ILED (mA)
60 40 20
16 14 12
0
0
2
4 VIN (V)
6
8
10
0
2
4 VIN (V)
6
8
May 2001 TOKO, Inc.
Page 9
TK11850L
DIMMING
The following are 3 kinds of dimming methods. 1. Dimming by RLED The current of the LED (ILED) is determined by RLED,which can be set by switches such as transistors. Example of 3 LEDs with a 4 brightness level circuit:
VIN CIN RSC GND IS VIN 0.1 V IS COMP EN BAND GAP REFERENCE 8 ON/OFF
+ -
OSC 0.86 V Cx 0.3 V 7 CX
ILED =
CX
CLK CLK L
VREF RLED
CLK EXT GND
D VOUT Q
S
RLED: Total value of Resistors VREF = 0.525 V (typ) VFB Voltage = 0.525 V (typ)
ERROR COMP
VFB
R
+ VREF 0.525 V
COUT VLED ILED RLED1 RLED2 RLED3
SW1
CONTROL SIGNAL 1
CONTROL SIGNAL 2 SW2
ILED vs. RLED
RLED (9) 24 27 36 51 100 510 ILED (mA) 21.9
ILED (mA)
20 18 16 14 12 10 8 6 4 2 0 10
LED CURRENT (ILED) vs. TOTAL RESISTANCE (RLED)
19.5 14.6 10.4 5.4 1.1
100 RLED ()
1000
Page 10
May 2001 TOKO, Inc.
TK11850L
2. PWM Dimming Apply the PWM signal to the EN Terminal (Pin no. 8). In this case, a signal frequency of approximately120 Hz is adequate. The average current of the LED changes due to the On/Off cycle of the IC, which follows the duty cycle of the PWM signal. Set the PWM signal at a high level over 2 V and a low level under 0.6 V, with a driving current over 2 mA.
VIN CIN RSC GND IS VIN 0.1 V IS COMP EN BAND GAP REFERENCE 8 ON/OFF
DIMMING (CONT)
+ -
OSC 0.86 V Cx 0.3 V 7 CX
CLK CLK L CX CLK EXT GND
LED CURRENT CURVE vs. PWM SIGNAL CURVE LED SETTING CURRENT LED CURRENT
D VOUT Q
S
Ton
ERROR COMP VFB
Toff
R
+ VREF 0.525 V
2.0 V PWM SIGNAL
(Applied to On/Off pin.)
0.6 V
fdim = 1 / T = 120 Hz Duty (%) = (Ton * 100) / T
COUT VLED ILED RLED
T
(LED CURRENT)
The PWM dimming LED current follows the PWM signal. (As shown above) The average LED current is obtained from the formula below. The graph below shows an example with ILED(MAX) (20 mA) at a Duty Cycle up to 100%. ILED(AVG) = ILED(MAX) * Duty ILED vs. DUTY 100
DUTY (%) 100 90 80 70 60 50 40 30 20 10 ILED (mA) 20.0 18.0 16.0
20 LED CURRENT (ILED) vs. DUTY CYCLE OF INPUT PWM SIGNAL 18 16 14
14.0 12.0
ILED (mA)
10.0 8.0 6.0 4.0 2.0
12 10 8 6 4 2 0 0 20 40 60 DUTY CYCLE (%) 80 100
May 2001 TOKO, Inc.
Page 11
TK11850L
Input PWM signal curve vs. LED current curve (ex. Three LEDs, Output current 20 mA)
LED CURRENT
(1) Duty Cycle = 80%
10 mA/Div 2.0 mSec/Div
PWM SIGNAL
(Applied to On/Off pin.)
1.0 V/Div 2.0 mSec/Div
(2) Duty Cycle = 50%
LED CURRENT
10 mA/Div 2.0 mSec/Div
PWM SIGNAL
(Applied to On/Off pin.)
1.0 V/Div 2.0 mSec/Div
(3) Duty Cycle = 20%
LED CURRENT
10 mA/Div 2.0 mSec/Div
PWM SIGNAL
(Applied to On/Off pin.)
1.0 V/Div 2.0 mSec/Div
Page 12
May 2001 TOKO, Inc.
TK11850L
DIMMING (CONT)
3. Dimming by DAC (D/A Converter) output Dimming is achievable by applying a DAC output to the VFB terminal with the addition of RDAC1 and RDAC2.
VIN CIN RSC GND IS VIN 0.1 V IS COMP EN BAND GAP REFERENCE 8 ON/OFF
+ -
OSC 0.86 V Cx 0.3 V 7 CX
CLK CLK L CX CLK EXT GND
D VOUT Q
S
ERROR COMP
VFB
R
+ VREF 0.525 V
DAC OUTPUT RDAC1
RDAC2
COUT VLED ILED RLED 1
Example Conditions: RDAC1 = RDAC2 RLED = 49 W
ILED vs. VDAC
DAC VOLTAGE (V) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 LED CURRENT (mA) 19.58 17.45 15.32 13.21 11.08 8.95 6.84 4.71 2.6 0.5
ILED (mA)
20 18 16 14 12 10 8 6 4 2 0 0 0.2 0.4 0.6 VDAC (V) 0.8 1 LED CURRENT (ILED) vs. DAC VOLTAGE (VDAC)
May 2001 TOKO, Inc.
Page 13
TK11850L
PACKAGE OUTLINE
SOT23L-8
0.45
Marking Information
Marking TK11850L
1.0
1850
8
5 Marking
e 0.8 1 e 0.8 4
+0.15
Recommended Mount Pad 0.1 Cl
0.3 - 0.05
3.5
+0.3 - 0.1
(3.4)
(0.3)
2.2
1.4max
1.2
e1 3.0
0 - 0.1
+0.15 - 0.15
0.4 3.3
+ 0.3
0.1
Dimensions are shown in millimeters Tolerance: x.x = 0.2 mm (unless otherwise specified)
Toko America, Inc. Headquarters 1250 Feehanville Drive, Mount Prospect, Illinois 60056 Tel: (847) 297-0070 Fax: (847) 699-7864
TOKOAMERICAREGIONALOFFICES
Midwest Regional Office Toko America, Inc. 1250 Feehanville Drive Mount Prospect, IL 60056 Tel: (847) 297-0070 Fax: (847) 699-7864 Western Regional Office Toko America, Inc. 2480 North First Street , Suite 260 San Jose, CA 95131 Tel: (408) 432-8281 Fax: (408) 943-9790 Semiconductor Technical Support Toko Design Center 4755 Forge Road Colorado Springs, CO 80907 Tel: (719) 528-2200 Fax: (719) 528-2375
Visit our Internet site at http://www.tokoam.com
The information furnished by TOKO, Inc. is believed to be accurate and reliable. However, TOKO reserves the right to make changes or improvements in the design, specification or manufacture of its products without further notice. TOKO does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of third parties which may result from the use of its products. No license is granted by implication or otherwise under any patent or patent rights of TOKO, Inc.
Page 14
(c) 1999 Toko, Inc. All Rights Reserved IC-XXX-TKXXXXX 0798O0.0K
0.15
15 max
May 2001 TOKO, Inc.
Printed in the USA

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