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CAT32 CMOS White LED Driver
Description
The CAT32 is a DC/DC step up converter that delivers a regulated output current. Operation at a constant switching frequency of 1.2 MHz allows the device to be used with very small value external inductor and ceramic capacitors. The CAT32 is targeted to drive multiple white light-emitting diodes (LEDs) connected in series and provides the necessary regulated current to control the brightness and the color purity. An external resistor RSET controls the output current level. LED currents of up to 40 mA can be supported over a wide range of input supply voltages from 2 V to 7 V, making the device ideal for battery-powered applications. A high voltage output stage allows up to 4 White LEDs to be driven in series. Series drive provides inherent current matching. LED dimming can be done by using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The shutdown input pin allows the device to be placed in power-down mode with "near zero" quiescent current. In addition to overcurrent limiting protection, the device also includes detection circuitry to ensure protection against open-circuit load fault conditions. The device is available in a low profile (1 mm max height) 6-lead TSOT-23 package.
Features
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1 TSOT-23 TD SUFFIX CASE 419AF
PIN CONNECTIONS
1 SW GND LED VIN SHDN RSET
TSOT-23 1 mm Maximum Height qJA = 250C/W (free air) (Top View)
* * * * * * * * * * * * *
Low Quiescent Ground Current (0.5 mA Typical) Power Efficiency Over 80% Compatible Pinout with LT1932 Adjustable Output Current (up to 40 mA) High Frequency 1.2 MHz Operation Input Voltage Operation down to 2.0 V Low Resistance (0.5 W) High Voltage Power Switch Drives up to 4 White LEDs in Series Shutdown Current Less than 1 mA Load Fault Protection Against Open-circuits Low Value External Components Low Profile (1 mm) TSOT-23 6-lead Package These Devices are Pb-Free, Halogen Free/BFR Free and are RoHS Compliant Color LCD and Keypad Backlighting Cellular Phones Handheld Terminals Digital Cameras PDAs/Games Portable MP3 Players
MARKING DIAGRAMS
LLYM
VFYM
LL = CAT32TDI-T3 VF = CAT32TDI-GT3 Y = Production Year (Last Digit) M = Production Month (1-9, A, B, C)
ORDERING INFORMATION
Device CAT32TDI-T3 CAT32TDI-GT3 Package TSOT-23 (Pb-Free) TSOT-23 (Pb-Free) Shipping 3,000/ Tape & Reel 3,000/ Tape & Reel
Applications
* * * * * *
(c) Semiconductor Components Industries, LLC, 2010
March, 2010 - Rev. 4
1
Publication Order Number: CAT32/D
CAT32
Typical Application Circuit
VIN 2.7 V to 4.2 V L1 6.8 mH D1 C1: Taiyo Yuden JMK212BJ475 C2: Taiyo Yuden EMK212BJ105 D1: Zetez ZHCS400 L1: Sumida CLQ4D106R8 (Panasonic ELJEA6R8)
C1 4.7 mF
6 VIN CAT32 5 SHDN RSET 4 RSET 1.50 kW
1 SW
PWM DIMMING CONTROL
LED GND 2
3 15 mA
C2 1 mF
TSOT-23 Pin Numbers
Figure 1. Li-Ion Driver for Four High-Brightness White LEDs Table 1. PIN DESCRIPTION
Pin Number SOT23 1 2 3 4 5 6 - Pin Number TDFN 8 5 6 4 3 2 1 Name SW GND LED RSET SHDN VIN Power Ground Function Switch pin. This is the drain of the internal power switch. For minimum EMI, minimize the trace area connected to this pin. Ground pin. Connect pin 2 to ground. LED (cathode) connection pin. RESET pin. A resistor connected from pin 4 to ground sets the LED current. This pin is also used to dim the LEDs. Shutdown pin. Input supply pin. This pin should be bypassed with a capacitor to ground. A 4.7 mF capacitor mounted close to the pin is recommended. Power Ground
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CAT32
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter VIN, LED, SHDN voltage SW voltage RSET voltage Storage Temperature Range Junction Temperature Lead Soldering Temperature (10 secs) ESD Rating - Human Body Model Rating 8 20 1 -65 to +150 125 300 2000 Unit V V V C C C V
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability.
Table 3. RECOMMENDED OPERATING CONDITIONS
Parameter VIN Ambient Temperature Range Inductor L1 Input Capacitor C1 Output Capacitor C2 ILED with 1 to 4 LEDs in series NOTE: Typical application circuit with external components is shown on page 2. Range 2 to 7 -40 to +85 6.8 20% typical 4.7 20% typical 1.0 20% typical 0 to 20 Unit V C mH mF mF mA
Table 4. ELECTRICAL OPERATING CHARACTERISTICS
(Over recommended operating conditions unless otherwise specified. TA = 25C, VIN = 2 V and VSHDN = 1.2 V.) Symbol IQ IGND VLED ILED ILED Parameter Quiescent Current Ground Current in Shutdown LED Pin Voltage LED Current Adjust Range Programmed LED Current RSET = 562 W RSET = 750 W RSET = 1.5 kW RSET = 4.53 kW ILED VRSET LED Pin Current Temperature Coefficient RSET Pin Voltage Shutdown Pin Logic High Level Shutdown Pin Logic Low Level fSW ISWL RSW Boost Converter Frequency Switch Current Limit Switch Resistance VIN = 2 V, ISW = 100 mA VIN = 3 V, ISW = 100 mA Switch Leakage Current Efficiency Switch Off, VSW = 5 V Components shown on Figure 1 0.8 400 1.2 550 0.7 0.5 0.01 83 ILED = 15 mA RSET = 1.5 kW 0.85 0.25 1.6 780 1.2 0.9 5 mA % Conditions VRSET = 0.2 V VSHDN = 0 V VIN < VOUT, ILED = 15 mA 5 33 25 12.5 38 30 15 5 -0.01 100 mA/C mV V V MHz mA W Min Typ 0.5 0.05 120 Max 0.7 1 180 40 45 36 17.5 Unit mA mA mV mA mA
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CAT32
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, TAMB = 25C, CIN = 4.7 mF, COUT = 1 mF, L = 6.8 mH, unless otherwise specified.) 600 QUIESCENT CURRENT (mA) QUIESCENT CURRENT (mA) 600 VIN = 7 V
500
500
VIN = 2 V 400
400
300
300
200
2
3
4
5
6
7
200 -50
-25
0
25
50
75
100
125
INPUT VOLTAGE (V)
TEMPERATURE (C)
Figure 2. Quiescent Current vs. Input Voltage
2.0 SWITCH FREQUENCY (MHz) 1.6 1.2 0.8 0.4 0 SWITCH FREQUENCY (MHz) 2.0 1.6 1.2 0.8 0.4
Figure 3. Quiescent Current vs. Temperature
2
3
4
5
6
7
0 -50
-25
0
25
50
75
100
125
INPUT VOLTAGE (V)
TEMPERATURE (C)
Figure 4. Switching Frequency vs. Input Voltage
35 30 LED CURRENT (mA) 25 20 15 10 5 0 2 3 4 5 6 7 0 -50 RSET = 1.13 kW RSET = 1.50 kW RSET = 2.26 kW RSET = 750 W LED CURRENT (mA) 15 20
Figure 5. Switching Frequency vs. Temperature
10
5
-25
0
25
50
75
100
125
INPUT VOLTAGE (V)
TEMPERATURE (C)
Figure 6. LED Current vs. Input Voltage
Figure 7. LED Current vs. Temperature
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CAT32
TYPICAL CHARACTERISTICS
(VIN = 3.6 V, TAMB = 25C, CIN = 4.7 mF, COUT = 1 mF, L = 6.8 mH, unless otherwise specified.) 1.0 SWITCH RESISTANCE (W) 0.8 0.6 0.4 0.2 0 SWITCH RESISTANCE (W) 1.0 0.8 0.6 0.4 0.2 0 -50
VIN = 3 V
2
3
4 INPUT VOLTAGE (V)
5
6
-25
0
25
50
75
100
125
TEMPERATURE (C)
Figure 8. Switch Resistance vs. Input Voltage
300 250 200 150 100 50 0
Figure 9. Switch Resistance vs. Temperature
LED PIN VOLTAGE (mV)
0
8
16
24
32
40
LED CURRENT (mA)
Figure 10. LED Pin Voltage vs. LED Current
85 80 EFFICIENCY (%) 75 70 65 60 4 LEDs at 15 mA VOUT = 13 V
Figure 11. VSW, IL, & VOUT Signal Waveforms
2
3
4 INPUT VOLTAGE (V)
5
6
Figure 12. Efficiency vs. Input Voltage
Figure 13. PWM on SHDN Pin Waveform
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CAT32
Operation The CAT32 device is a high efficiency, constant frequency, current regulating boost converter. The device includes a switch and an internally compensated loop for the regulation of the LED current. Operation can be best understood by examining the block diagram. The RSET pin is regulated at 100 mV and the current through the external resistor will set the regulated current in the LEDs (from 5 mA to 40 mA) with a multiplication factor of 225. Block Diagram
VIN C1 Over Voltage Protection (22 V) L1 1 SW D1 C2
While maintaining LED current regulation, the CAT32 automatically adjusts the LED pin voltage to be as low as possible. A low LED pin voltage ensures high efficiency. Current through the internal power switch is continuously monitored cycle-by-cycle. If the current limit is exceeded, the switch is immediately turned off, protecting the device, for the remainder of the cycle. PWM dimming operation can be achieved by switching the SHDN pin or by pulling the RSET pin higher than 0.1 V.
1.2 MHz Oscillator - + LED 3 ILED
PWM & Logic + Current Sense - Amp 6 5 VIN SHDN IS CAT32 2 GND 4 RSET RSET
100 mV
Current Control 225x
ILED = 225 x IS
Figure 14. CAT32 Block Diagram
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CAT32
Application Information
Inductor Selection and Efficiency
Inductor vendors are shown below. Contact the manufacturer for detailed technical data and new product information.
Table 5. INDUCTOR MANUFACTURERS
Inductor ELJEA4R7 ELJEA6R8 LQH3C4R7M24, LQH32CN4R7M11 LQH3C100K24, LQH32CN100K11 LB2016B4R7 LB2016B100 CMD4D06-4R7 CMD4D06-6R8 CLQ4D10-4R7 CLQ4D10-6R8 L (mH) 4.7 6.8 4.7 Maximum DCR (mW) 180 250 260 Maximum Height (mm) 2.2 2.2 2.2 Vendor Panasonic 714.373.7334 Web www.panasonic.com
Murata 770.436.1300
www.murata.com
10 4.7 3.8 4.7 6.8 4.7 6.8
300 250 350 216 296 162 195
2.2 2.0 2.0 0.8 0.8 1.2 1.2 Sumida 847.956.0666 www.sumida.com Taiyo Yuden 408.573.4150
www.t-yuden.com
Capacitor Selection
Diode Selection
Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. The low ESR and small package options available with multilayer ceramic capacitors make them excellent choices. The X5R and X7R capacitor types are preferred because they retain their capacitance over wider voltage and temperature ranges than the Y5V or Z5U types. A 1.0 mF or 2.2 mF output capacitor is recommended for most applications. The voltage rating of the output capacitor C2 depends on the number of LEDs driven in series. A 10 V ceramic capacitor is recommended when driving two LEDs. A 16 V ceramic capacitor is recommended when driving 3 or 4 LEDs.
Table 6. CERAMIC CAPACITOR MANUFACTURERS
Supplier Taiyo Yuden Murata Kemet Phone 408.573.4150 814.237.1431 408.986.0424 Web www.t-yuden.com www.murata.com www.kemet.com
Schottky diodes, with their low forward voltage drop and fast switching speed, are the ideal choice for high efficiency applications. Table 7 shows several different Schottky diodes that work well with the CAT32. Make sure that the diode has a voltage rating greater than the output voltage. The diode conducts current only when the power switch is turned off (typically less than one-third the time), so a 0.4 A or 0.5 A diode will be sufficient for most designs.
Table 7. SCHOTTKY DIODE SUPPLIERS
Part MBR0520 MBR0530 s MBR0540 ZHCS400 Supplier ON Semiconductor www.onsemi.com 800.282.9855 Zetex
LED Current Programming
Low profile ceramic capacitors with a 1 mm maximum height/thickness are available for designs height requirements. Ceramic capacitors also make a good choice for the input capacitor, which should be mounted as close as possible to the CAT32. A 2.2 mF or 4.7 mF input capacitor is recommended. Table 6 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information as new products and package options are introduced regularly.
The LED current is programmed with a single resistor connected to the RSET pin. The RSET pin is internally regulated to 100 mV, which sets the current flowing out of this pin, ISET, equal to 100 mV/RSET. The CAT32 regulates the current into the LED pin, ILED, to 225 times the value of ISET. For the best accuracy, a 1% or better resistor is recommended. Table 8 shows several typical 1% RSET values.
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CAT32
Table 8. RSET RESISTOR VALUES
ILED (mA) 40 30 25 20 15 10 5 RSET 562 W 750 W 909 W 1.13 kW 1.50 kW 2.26 kW 4.53 kW
For other LED current values, use the following equation to choose RSET.
R SET + 255 0.1 V I LED
In addition to providing the widest dimming range, PWM brightness control also ensures the "purest" white LED color over the entire dimming range. The true color of a white LED changes with operating current, and is the "purest" white at a specific forward current, usually 15 mA or 20 mA. If the LED current is less than or more than this value, the emitted light becomes more blue. Applications involving color LCDs can find the blue tint objectionable. When a PWM control signal is used to drive the SHDN pin of the CAT32, the LEDs are turned off and on at the PWM frequency. The current through them alternates between full current and zero current, so the average current changes with duty cycle. This ensures that when the LEDs are on, they can be driven at the appropriate current to give the purest white light. LED brightness varies linearly with the PWM duty cycle.
LED Dimming with a Logic Signal
Most white LEDs are driven at maximum currents of 15 mA to 20 mA. Some higher power designs will use two parallel strings of LEDs for greater light output, resulting in 30 mA to 40 mA (two strings of 15 mA to 20 mA) flowing into the LED pin.
LED Dimming with PWM Signal
For applications that need to adjust the LED brightness in discrete steps, a logic signal can be used. RMIN sets the minimum LED current value (when the NMOS is OFF):
R MIN + 255 0.1 V I LED(MIN)
PWM brightness control provides the widest dimming range (greater than 20:1). By turning the LEDs ON and OFF using the control signal the LEDs operate at either zero or full current, but their average current changes with the PWM signal duty cycle. Typically, a 5 kHz to 40 kHz PWM signal is used. PWM dimming with the CAT32 can be accomplished two different ways. The SHDN pin can be driven directly or a resistor can be added to drive the RSET pin. If the SHDN pin is used, increasing the duty cycle will increase the LED brightness. Using this method, the LEDs can be dimmed and turned off completely using the same control signal. A 0% duty cycle signal will turn off the CAT32, reducing the total quiescent current to near zero. If the RSET pin is used, increasing the duty cycle will decrease the brightness. Using this method, the LEDs are dimmed using RSET and turned off completely using SHDN. If the RSET pin is used to provide PWM dimming, the approximate value of RPWM should be calculated (where VMAX is the "HIGH" value of the PWM signal):
R PWM + R SET V MAX *1 0.15 V
RINCR determines how much LED current increases when the external NMOS switch is turned ON.
R INCR + 255 0.1 V I LED(Increase)
LED Dimming with a DC Voltage R ADJ + 225 V MAX * 0.1 V I LED(MAX) * I LEAD(MIN)
PCB Layout Guidelines The CAT32 is a high-frequency switching regulator and therefore proper PCB board layout and component placement can minimize noise and radiation and increase efficiency. To maximize efficiency, the CAT32 design has fast switch rise and fall times. To prevent radiation and high frequency resonance problems minimize the length and area of all traces connected to the SW pin and use a ground plane under the switching regulator. The switch, schottky output diode and output capacitor signal path should be kept as short as possible. The ground connection for the RSET resistor should be tied directly to the GND pin and not be shared with other components.
CAT32 CAT32 RSET 4 RINCR Logic Signal
CAT32 SHDN 5
CAT32 RSET 4 RSET RPWM
CAT32 RSET 4 RSET 10 kW 0.1 mF RPWM
PWM
PWM
PWM
RSET 4 RSET RADJ
VDC
RMIN
Figure 15. LED Dimming Circuits http://onsemi.com
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CAT32
TYPICAL APPLICATION CIRCUITS
(The application diagrams below are shown for the TSOT-23 packages.) VIN 6 VIN C1 4.7 mF CAT32 5 SHDN LED GND 2 3 15 mA L1 6.8 mH 1 SW C2 2.2 mF D1
2.5 V DC DIMMING CONTROL
RSET 4 60.40 kW RSET 1.50 kW
Figure 16. Two LEDs with DC Level Dimming Control
VIN 6 VIN C1 4.7 mF CAT32 5 SHDN RSET 4 LED GND 2 3 15 mA L1 6.8 mH 1 SW C2 1 mF EFFICIENCY (%) D1 85 VIN = 4.2 V 80 75 70 65 60 VIN = 3.0 V
2.5 V DC 60.40 kW DIMMING CONTROL
RSET 1.50 kW
0
5
10 LED CURRENT (mA)
15
20
Figure 17. Three LEDs with DC Level Dimming Control
VIN L1 6.8 mH D1 85 C1 4.7 mF 80 VIN PWM DIMMING CONTROL CAT32 5 SHDN RSET 4 RSET 1.50 kW LED GND 2 3 15 mA C2 1 mF SW EFFICIENCY (%) 6 1 75 70 65 60
Figure 18. Efficiency - Three LEDs
VIN = 4.2 V VIN = 3.0 V
0
5
10 LED CURRENT (mA)
15
20
Figure 19. Four LEDs with PWM Dimming Control
Figure 20. Efficiency - Four LEDs
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CAT32
PACKAGE DIMENSIONS
TSOT-23, 6 LEAD CASE 419AF-01 ISSUE O SYMBOL
A A1 A2 b c D E1 E E E1 e L L1 L2 0.30 0.01 0.80 0.30 0.12 0.15 2.90 BSC 2.80 BSC 1.60 BSC 0.95 TYP 0.40 0.60 REF 0.25 BSC 0.50 0.05 0.87
D e
MIN
NOM
MAX
1.00 0.10 0.90 0.45 0.20
TOP VIEW
0
8
A2 A
q
b
A1 L1
L
c
L2
SIDE VIEW Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC MO-193.
END VIEW
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CAT32
Example of Ordering Information (Note 3)
Prefix CAT Device # 32 Suffix TD I -G T3
Company ID (Optional)
Product Number 32
Package TD: TSOT-23
Temperature Range I = Industrial (-40C to +85C)
Lead Finish G: NiPdAu
Tape & Reel (Note 5) T: Tape & Reel 3: 3,000 / Reel
1. 2. 3. 4. 5.
All packages are RoHS-compliant (Lead-free, Halogen-free). The standard lead finish is NiPdAu. The device used in the above example is a CAT32TDI-GT3 (TSOT-23, Industrial Temperature Range, NiPdAu, Tape & Reel, 3,000 / Reel). For additional package and temperature options, please contact your nearest ON Semiconductor Sales office. For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D.
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303-675-2175 or 800-344-3860 Toll Free USA/Canada Fax: 303-675-2176 or 800-344-3867 Toll Free USA/Canada Email: orderlit@onsemi.com N. American Technical Support: 800-282-9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81-3-5773-3850 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative
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CAT32/D

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