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CAT37
CMOS White LED Driver Boost Converter
FEATURES
Low quiescent ground current (0.5mA typical) Power efficiency over 80% Compatible pinout with LT1937 Adjustable output current (up to 40mA) High frequency 1.2MHz operation Input voltage operation down to 2.5V Low resistance (0.5) power switch Drives up to 4 White LEDs in series Shutdown current less than 1A Load fault protection against open-circuits Low value external components Low profile (1mm) TSOT-23 5-lead package
DESCRIPTION
The CAT37 is a DC/DC step up converter that delivers a regulated output current. Operation at a constant switching frequency of 1.2MHz allows the device to be used with very small value external inductor and ceramic capacitors. The CAT37 is targeted to drive multiple white lightemitting diodes (LEDs) connected in series and provides the necessary regulated current to control the brightness and the color purity. An external resistor R1 controls the output current level. LED currents of up to 40mA can be supported over a wide range of input supply voltages from 2.5V to 7V, 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 (1mm max height) 5-lead TSOT-23 package.
L1 6.8H
APPLICATION
Color LCD and keypad backlighting Cellular phones Handheld terminals Digital cameras PDAs/Games Portable MP3 players For Ordering Information details, see page 11.
TYPICAL APPLICATION CIRCUIT
VIN 3V to 5V C1 1F
D1
5 VIN CAT37
1 SW
C2 1F
ON OFF
4
SHDN GND 2
FB
3
15mA
C1: Taiyo Yuden JMK212BJ475 C2: Taiyo Yuden EMK212BJ105 L1: Panasonic ELJEA6R8 or equivalent
R1 6.34
Figure 1. Driver for Four High-Brightness White LEDs
(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
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Doc. No. MD-5005 Rev. V
CAT37
ORDERING INFORMATION
Part Number CAT37TDI-T3 CAT37TDI-GT3 Package TSOT-23 5-lead (1) TSOT-23 5-lead (2) Quantity per Reel 3,000 3,000 Package Marking LM UL
PIN CONFIGURATION
TSOT-23 5-Lead Top View
SW GND FB 1 2 3 4 SHDN 5 VIN
1mm maximum height JA = 250C/W [free air]
PIN DESCRIPTION
Pin Number 1 2 3 4 5 Name SW GND FB 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. Shutdown pin. Input supply pin. This pin should be bypassed with a capacitor to ground. A 1F capacitor mounted close to the pin is recommended.
SHDN
VIN
Notes: (1) Matte-Tin Plated Finish (RoHS-compliant). (2) NiPdAu Plated Finish (RoHS-compliant).
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(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
CAT37
ABSOLUTE MAXIMUM RATINGS
Parameter VIN, FB, voltage SHDN SW voltage Storage Temperature Range Junction Temperature Lead Soldering Temperature (10 secs) ESD Rating - Human Body Model
(1)
Rating 8 20 -65 to +160 125 300 2000
Unit V V C C C V
RECOMMENDED OPERATING CONDITIONS
Parameter VIN Ambient Temperature Range Inductor L1 Input Capacitor C1 Output Capacitor C2 ILED with 1 to 4 LEDs in series Range 2.5 to 7 -40 to +85 6.8 20% typical 1.0 20% typical 1.0 20% typical 0 to 20 Unit V C H F F mA
Typical application circuit with external components is shown on page 1.
ELECTRICAL OPERATING CHARACTERISTICS
Over recommended operating conditions unless otherwise specified. TA = 25C, VIN = 3V and V = 3V. SHDN Symbol IQ ISD VFB IFB Parameter Input Voltage Range Quiescent Current Shutdown Current FB Pin Voltage FB Pin Leakage Current Shutdown High Threshold Shutdown Low Threshold ISHDN fSW DC ISWL Shutdown Pin Current Boost Converter Frequency Maximum Switch Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current Efficiency ISW = 300 mA Switch Off, VSW = 5 V Figure 1 with specified components 0.8 90 400 1.2 95 550 150 0.01 83 780 200 5 0.85 0.25 1 1.6 VFB = 0.2 V VSHDN = 0 V 4 LEDs at 15 mA 85 Conditions Min 2.5 0.5 0.05 95 1 Typ Max 7 0.7 1 105 2 Units V mA A mV A V V nA MHz % mA mV A %
Notes: (1) These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground.
(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
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Doc. No. MD-5005 Rev. V
CAT37
TYPICAL CHARACTERISTICS
VIN = 3.6V, TAMB = 25C, CIN = 4.7F, COUT = 1F, L = 6.8H, unless otherwise specified.
LED Current vs. Input Voltage
30 3 3 LEDs LEDs 16.0
LED Current vs. Temperature
LED CURRENT [mA]
20
LED CURRENT [mA]
20mA 20mA
15.5
15.0 4 4 LEDs LEDs 14.5
10mA 10mA 10
0 2 3 4 INPUT VOLTAGE [V] 5 6
14.0 -50 -25 0 25 50 75 100
TEMPERATURE [C]
FB Pin Voltage vs. LED Current
110 105 100
FB Pin Voltage vs. Temperature
FB PIN VOLTAGE [mV]
100 95 90 85 80 0 5 10 LED CURRENT [mA]
3 LEDs 3 LEDs
FB PIN VOLTAGE [mV]
95
90
85
4 LEDs at 15mA 4LEDs at 15mA VIN = 3.6V VIN = 3.6V
80 15 20 -50 -25 0 25 50 75 100 TEMPERATURE [C]
Switching Frequency vs. Input Voltage
1.3 1.3
Switching Frequency vs. Temperature
SWITCHING FREQUENCY [MHz]
SWITCH FREQUENCY [MHz]
1.2
1.2
1.1
1.1 LOAD = mA LOAD =20 20mA 1.0 LOAD ==33LEDs VIN LOAD LEDs =VIN = 3.6V 3.6V
1.0
0.9 4 LEDs 4 LEDs 0.8 1 2 3 4 5 6
0.9
0.8 -50 -25 0 INPUT VOLTAGE [V] 25 50 TEMPERATURE [C] 75 100
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(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
CAT37
TYPICAL CHARACTERISTICS
VIN = 3.6V, TAMB = 25C , CIN = 4.7F, COUT = 1F, L = 6.8H, unless otherwise specified.
Efficiency vs. Input Voltage
90 85 86 LOAD = 20 mA 84
Efficiency vs. Temperature
EFFICIENCY [%]
80 75 70 65 60 2 3 4 5 6 3 3 LEDs at 15mA LEDS at 15mA VOUT = = 10V VOUT 10V
EFFICIENCY [%]
82 80 78 76 74 -50 -25 LOAD = 3 LEDs = VIN = 3.6V 3.6V
LOAD = 15 mA LOAD = 10 mA
INPUT VOLTAGE [V]
0 25 50 TEMPERATURE [C]
75
100
VSW, IL, & VOUT Waveforms
PWM on SHDN pin at 1kHz
Enable Power-Up Waveforms
(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
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Doc. No. MD-5005 Rev. V
CAT37
OPERATION
The CAT37 device is a high efficiency, constant frequency, current regulating boost driver for white LEDs. The device includes a switch and an internally compensated loop for the regulation of the current in the LEDs. Operation can be best understood by examining the block diagram. The FB pin is regulated at 95mV and the current through the external resistor will set the regulated current in the LEDs at:
ILED = 0.095 R1
While maintaining LED current regulation, the CAT37 boost converter automatically adjusts the FB pin voltage to be as low as possible. A low FB 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 pin or by pulling the FB pin SHDN higher than 95mV.
BLOCK DIAGRAM
L1 VIN C1 VIN 4 SHDN Over Voltage Protection (22V) 5 1 SW C2 D1
1.2MHz Oscillator
90k 6k ILED FB 3 Error Amp R1 0.095V REF
PWM & Logic
Current Sense Amp CAT37 GND 2
Figure 2. CAT37 Block Diagram
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(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
CAT37
APPLICATION INFORMATION
CAPACITOR 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 1.0F output capacitor is recommended for most applications. The voltage rating of the output capacitor C2 depends on the number of LEDs driven in the series. A 16V ceramic capacitor is recommended when driving 3 or 4 LEDs. Low profile ceramic capacitors with a 1mm 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 CAT37. A 1F or 4.7F input capacitor is recommended. Table 1 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information as new products and package options are introduced regularly. Table 1: Ceramic Capacitor Manufacturers Supplier Taiyo Yuden Murata Kemet AVX Web www.t-yuden.com www.murata.com www.kemet.com www.avxcorp.com For other LED current values, use the following equation to choose R1.
R1 = 0.095 ILED
Table 2: Schottky Diode Suppliers Part MBR0520 MBR0530 MBR0540 Supplier ON Semiconductor www.onsemi.com 800.282.9855
LED CURRENT PROGRAMMING The LED current is programmed with a single resistor connected to the FB pin. The FB pin is internally regulated to 95 mV, which sets the current flowing through R1 and the LEDs as equal to 0.095/R1. For the best accuracy, a 1% or better resistor is recommended. Table 3 shows several typical 1% R1 values. Table 4: R1 Resistor Values ILED (mA) 40 30 20 15 12 10 5 R1 () 2.37 3.16 4.75 6.34 7.87 9.53 19.1
DIODE SELECTION Schottky diodes, with their low forward voltage drop and fast switching speed, are the ideal choice for high efficiency applications. Table 2 shows several different Schottky diodes that work well with the CAT37. 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 0.4A or 0.5A diode will be sufficient for most designs.
Most white LEDs are driven at maximum currents of 15mA to 20mA. Some higher power designs will use two parallel strings of LEDs for greater light output, resulting in 30mA to 40mA (two strings of 15mA to 20mA) flowing through the R1 resistor.
(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
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Doc. No. MD-5005 Rev. V
CAT37
LED DIMMING WITH DC SIGNAL Dimming the LEDs can be done by applying a variable DC voltage as shown on Figure 3. As the VDC increase the voltage across R1 decreases and therefore lower the LED current. The resistors R2 and R3 must be large enough so that their current (tens of A) is much smaller than the LED current but much larger than the FB leakage current (IFB). When adjusting VDC between 0V and 2V, the resistors shown on Figure 3 will set the LED current between 0mA and 15mA. LED DIMMING WITH PWM SIGNAL 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 5kHz to 40kHz PWM signal is used. A filtered PWM signal is used to dim the LEDs, as shown in Figure 4. 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 15mA or 20mA. 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.
RINCR = 0.095 V ILED(INCREASE )
LED DIMMING WITH A LOGIC SIGNAL For applications that need to adjust the LED brightness in discrete steps, a logic signal can be used as shown in Figure 5. R1 sets the minimum LED current value (when the NMOS switch is OFF):
R1 = 0.095 V ILED(MIN)
RINCR determines how much LED current increases when the external NMOS switch is turned ON.
PCB LAYOUT GUIDELINES The CAT37 is a high-frequency switching regulator where proper PCB board layout and component placement can minimize noise and radiation and increase efficiency. To maximize efficiency, the CAT37 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 SW pin, schottky diode and capacitor C2 signal path should be kept as short as possible. The ground connection for the R1 resistor should be tied directly to the GND pin and not be shared with other components.
CAT37 FB R3 180k VDC R1 6.3 R2 10k PWM 10k
CAT37 FB R3 180k R2 10k R1 6.3
CAT37 FB RINCR Logic Signal R1 6.3
0.1F
2N7002
Figure 3. Dimming with a DC Voltage
Figure 4. Dimming with a Filtered PWM Signal
Figure 5. Dimming with a Logic Signal
Doc. No. MD-5005 Rev. V
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(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
CAT37
TYPICAL APPLICATION CIRCUITS
Two LEDs with DC Level Dimming Control
L1 6.8H D1
90 VIN = 3.6V VIN = 3.6V VIN = 3.0V VIN = 3.0V
Efficiency - Two LEDs
VIN 3V to 4.2V C1 1F VDC Dimming 5 VIN CAT37 4 SHDN GND 2 FB 3 1 SW C2 1F
85
EFFICIENCY [%]
80 75 70 65 60
180k 15mA 10k
R1 6.34
0
5
10
15
20
25
30
LED CURRENT [mA]
Three LEDs with DC Level Dimming Control
L1 6.8H D1
90
Efficiency -- Three LEDs
VIN 3V to 4.2V C1 1F VDC Dimming 5 VIN CAT37 4 SHDN GND 2 FB 3 1 SW C2 1F
85
VIN = 3.6V VIN=3.6V VIN =VIN=3.0V 3.0V
EFFICIENCY [%]
80 75 70 65 60
180k 15mA 10k
R1 6.34
0
5
10
15
20
25
30
LED CURRENT [mA]
Four LEDs with PWM Dimming Control
L1 6.8H D1 PWM C1 1F 10k 5 VIN CAT37 4 SHDN GND 2 FB 3 10k R1 6.34 1 SW 180k 15mA 0.1F C2 1F VIN 3V to 4.2V
90 85
Efficiency - Four LEDs
EFFICIENCY [%]
VIN = 3.6V VIN=3.6V
80 75 70 65 60 0 5 10 15 20 LED CURRENT [mA] 25 30
VIN=3.0V VIN = 3.0V
(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
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Doc. No. MD-5005 Rev. V
CAT37
PACKAGE OUTLINE DRAWING
TSOT-23 5-Lead (TD) (1)(2)
D e
SYMBOL A A1 A2 b c D
E1 E
MIN 0.01 0.80 0.30 0.12
NOM 0.05 0.87 0.15 2.90 BSC 2.80 BSC 1.60 BSC 0.95 TYP
MAX 1.00 0.10 0.90 0.45 0.20
E E1 e L L1 L2 0 0.30
0.40 0.60 REF 0.25 BSC
0.50
8
TOP VIEW
A2 A
b
A1 L1
L
c
L2
SIDE VIEW
END VIEW
For current Tape and Reel information, download the PDF file from: http://www.catsemi.com/documents/TapeandReel.pdf
Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC standard MO-193.
Doc. No. MD-5005 Rev. V
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(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
CAT37
EXAMPLE OF ORDERING INFORMATION 1
Prefix CAT
Device # 37
Suffix TD I -G T3
Product Number 37 Optional Company ID
Industrial Temperature I: Range -40C to + 85C
Tape & Reel T: Tape & Reel 3: 3,000/Reel
Package TD: TSOT-23
Lead Finish Blank: Matte-Tin G: NiPdAu
Notes: (1) All packages are RoHS-compliant (Lead-free, Halogen-free). (2) The standard lead finish is NiPdAu. (3) The device used in the above example is a CAT37TDI-GT3 (TSOT-23, NiPdAu, Tape & Reel, 3,000/Reel). (4) For additional package and temperature options, please contact your nearest ON Semiconductor Sales office.
(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
11
Doc. No. MD-5005 Rev. V
CAT37
REVISION HISTORY
Date Rev. Reason Updated Ordering Information - part numbers Changed L1 for each figure from 22H to 6.8H Changed VIN for Typical Application from 2.7V to 4.2V to 3V to 5V Changed C1 for each typical application circuit from 4.7F to 1F Changed C2 for each typical application circuit from 2.2F to 1F Changed VIN for each for each typical application circuit from 1.8V to 3V to 3V to 4.2V Updated Ordering Information - part numbers Updated Features Changed R1 for Typical Application figure and Typical Application Circuit figures from 6.34 to 6.8 Updated Description (2V to 2.5V input supply voltage) Updated Ordering Information (added package marking code) Updated Electrical Specifications Updated Table 4 (R1 Resistor Value) with new values Updated LED dimming with logic signal (0.095V to 0.105V) Updated Typical Application figures Updated Electrical Specifications Updated Operation text Updated LED current programming text Updated Table 4 (R1 Resistor Value) with new values Updated LED dimming equations Updated Typical Application Circuit figures Updated FB Pin Leakage Current in Electrical Specifications Added Typical Characteristics graphs (pages 4-6) Added Efficiency graphs to Typical Application Circuits Changed package drawing for 5-lead SOT-23 Updated Absolute Maximum Ratings Deleted temp range from Electrical Specifications Added Recommended Operating Conditions Updated Block Diagram Updated Electrical Specifications (changed VRSET to VFB in IQ) Removed Preliminary data sheet designation Added Green Packages in all areas Eliminated TDFN (3 x 4.9mm) package Updated Ordering Information Update Features Update Description Update Ordering Information Update Pin Configuration Update Pin Description Update Block Diagram Update Package Outlines Add TSOT-23 in NiPdAu plated finish Add Example of Ordering Information Update Package Outline Drawing Add MD- to document number Change logo and fine print to ON Semiconductor Update Typical Application Circuits
25-Sept-03
H
25-Sept-03
I
06-Nov-03
J
08-Dec-03
K
10-Dec-03 18-Dec-03
L M
22-Dec-03 9-June-04 15-June-04 22-Sept-04 01-Nov-04
N O P Q R
07-July-05
S
19-May-08 11-Nov-08 15-Apr-09
T U V
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(c) 2009 SCILLC. All rights reserved. Characteristics subject to change without notice
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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