View CAT4237TD-GT3_4192628.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

CAT4237
High Voltage CMOS Boost White LED Driver
FEATURES
Drives 6 to 8 White LEDs in series from 3V Up to 87% Efficiency Low Quiescent Ground Current 0.6mA Adjustable Output Current (up to 40mA) High Frequency 1MHz Operation High Voltage Power Switch Shutdown current less than 1A Open LED low power mode Automatic Shutdown at 1.9V (UVLO) Thermal shutdown protection RoHS-compliant Thin SOT23 5-Lead (1mm max height)
DESCRIPTION
The CAT4237 is a DC/DC step-up converter that delivers an accurate constant current ideal for driving LEDs. Operation at a constant switching frequency of 1MHz allows the device to be used with small value external ceramic capacitors and inductor. LEDs connected in series are driven with a regulated current set by the external resistor R1. LED currents up to 40mA can be supported over a wide range of input supply voltages from 2.8V to 5.5V, making the device ideal for battery-powered applications. The CAT4237 highvoltage output stage is perfect for driving six, seven or eight white LEDs in series with inherent current matching in LCD backlight applications. 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 "zero" quiescent current. In addition to thermal protection and overload current limiting, the device also enters a very low power operating mode during "Open LED" fault conditions. The device is housed in a low profile (1mm max height) 5-lead thin SOT23 package for space critical applications.
APPLICATIONS
Color LCD and keypad Backlighting Cellular Phones Handheld Devices Digital Cameras PDAs Portable Game Machine
ORDERING INFORMATION
Part Number CAT4237TD-T3 Package TSOT23-5 (1) Quantity per Reel 3000 3000 Package Marking LT UD
For Ordering Information details, see page 13.
CAT4237TD-GT3 TSOT23-5 (2)
Notes: (1) Matte-Tin Plated Finish (RoHS-compliant). (2) NiPdAu Plated Finish (RoHS-compliant).
PIN CONFIGURATION
5-Lead Thin SOT23 (1mm max height)
TYPICAL APPLICATION CIRCUIT
VIN 3V to 4.2V C1 VIN
4 SHDN
L 33H
D C2 SW 0.22F
VOUT
SW 1 GND 2 FB 3
5 VIN
4.7F
CAT4237 OFF ON SHDN GND
L: Sumida CDRH3D16-330 D: Central CMDSH05-4 (rated 40V) C2: Taiyo Yuden UMK212BJ224 (rated 50V)
FB
VFB = 300mV R1 15
20mA
Top View
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
1
Doc. No. MD-5013, Rev. B
CAT4237 ABSOLUTE MAXIMUM RATINGS
Parameters VIN, FB voltage SHDN voltage SW voltage Storage Temperature Range Junction Temperature Range Lead Temperature Ratings -0.3 to +7 -0.3 to +7 -0.3 to 55 -65 to +160 -40 to +150 300 Units V V V C C C
RECOMMENDED OPERATING CONDITIONS
Typical application circuit with external components are shown on page 1. Parameters VIN SW pin voltage Ambient Temperature Range 6, 7 or 8 LEDs Range 2.8 to 5.5 0 to 30 -40 to +85 1 to 40 Units V V C mA
Note: (1) Thin SOT23-5 package thermal resistance JA = 135C/W when mounted on board over a ground plane.
DC ELECTRICAL CHARACTERISTICS
VIN = 3.6V, ambient temperature of 25C (over recommended operating conditions unless specified otherwise). Symbol IQ ISD VFB IFB ILED VIH VIL FSW ILIM RSW ILEAK Parameter Operating Current Shutdown Current FB Pin Voltage FB pin input leakage Programmed LED Current SHDN Logic High SHDN Logic Low Switching Frequency Switch Current Limit Switch "On" Resistance Switch Leakage Current Thermal Shutdown Thermal Hysteresis Undervoltage Lockout (UVLO) Threshold Overvoltage Threshold ISW = 100mA Switch Off, VSW = 5V R1 = 10 R1 = 15 R1 = 20 Enable Threshold Level Shutdown Threshold Level 28.5 19 14.25 0.4 0.8 350 30 20 15 0.8 0.7 1.0 450 1.0 1 150 20 1.9 35 Conditions VFB = 0.2V VFB = 0.4V (not switching) VSHDN = 0V 8 LEDs with ILED=20mA Min Typ 0.6 0.1 0.1 300 Max 1.5 0.6 1 315 1 31.5 21 15.75 1.5 1.3 600 2.0 5 Unit mA A mV A mA V V MHz mA A C C V V
285
VUVLO VOV-SW
Doc. No. MD-5013, Rev. B
2
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
CAT4237 PIN DESCRIPTION
VIN is the supply input for the internal logic The device is compatible with supply voltages down to 2.8V and up to 5.5V. It is recommended that a small bypass ceramic capacitor (4.7F) be placed between the VIN and GND pins near the device. If the supply voltage drops below 1.9V, the device stops switching. SHDN is the shutdown logic input. When the pin is tied to a voltage lower than 0.4V, the device is in shutdown mode, drawing nearly zero current. When the pin is connected to a voltage higher than 1.5V, the device is enabled. GND is the ground reference pin. This pin should be connected directly to the ground place on the PCB. SW pin is connected to the drain of the internal CMOS power switch of the boost converter. The inductor and the Schottky diode anode should be connected to the SW pin. Traces going to the SW pin should be as short as possible with minimum loop area. An overvoltage detection circuit is connected to the SW pin. When the voltage reaches 35V, the device enters a low power operating mode preventing the SW voltage from exceeding the maximum rating. FB feedback pin is regulated at 0.3V. A resistor connected between the FB pin and ground sets the LED current according to the formula: ILED = 0.3V/R1 The lower LED cathode is connected to the FB pin.
PIN DESCRIPTIONS
Pin # 1 2 3 4 5 Name SW GND FB SHDN VIN Function Switch pin. This is the drain of the internal power switch. Ground pin. Connect the pin to the ground plane. Feedback pin. Connect to the last LED cathode. Shutdown pin (Logic Low). Set high to enable the driver. Power Supply input.
BLOCK DIAGRAM
33H VIN C1 4.7F 1MHz Oscillator VIN - VREF 300mV A1 RC CC RS + GND Over Voltage Protection PWM & Logic Driver N1 LED Current SW C2 0.22F
+ -
Enable Thermal Shutdown & UVLO
A2
SHDN
Current Sense
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
3
-
+
FB R1 15
Doc. No. MD-5013, Rev. B
CAT4237 DEVICE OPERATION
The CAT4237 is a fixed frequency (1MHz), low noise, inductive boost converter that provides a constant current with excellent line and load regulation. The device uses a high-voltage CMOS power switch between the SW pin and ground to energize the inductor. When the switch is turned off, the stored energy in the inductor is released into the load via the Schottky diode. The on/off duty cycle of the power switch is internally adjusted and controlled to maintain a constant regulated voltage of 0.3V across the feedback resistor connected to the feedback pin (FB). The value of the resistor sets the LED current accordingly (0.3V/R1). During the initial power-up stage, the duty cycle of the internal power switch is limited to prevent excessive in-rush currents and thereby provide a "soft-start" mode of operation. While in normal operation, the device can deliver up to 40mA of load current into a string of up to 8 white LEDs. In the event of a "Open LED" fault condition, where the feedback control loop becomes open, the output voltage will continue to increase. Once this voltage exceeds 35V, an internal protection circuit will become active and place the device into a very low power safe operating mode where only a small amount of power is transferred to the output. This is achieved by pulsing the switch once every 60s and keep it on for about 1s only. Thermal overload protection circuitry has been included to prevent the device from operating at unsafe junction temperatures above 150C. In the event of a thermal overload condition the device will automatically shutdown and wait till the junction temperatures cools to 130C before normal operation is resumed. Light Load Operation Under light load condition (under 4mA) and with input voltage above 4.2V, the CAT4237 driving 6 LEDs, the driver starts pulse skipping. Although the LED current remains well regulated, some lower frequency ripple may appear.
Figure 1. Switching Waveform VIN = 4.2V, ILED = 4mA
Doc. No. MD-5013, Rev. B
4
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
CAT4237
TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7F, COUT = 0.22F, L = 33H with 8 LEDs at 20mA, TAMB = 25C, unless otherwise specified. Quiescent Current vs. VIN (Not Switching)
140 120 INPUT CURRENT [uA] 100 80 60 40 20 0 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 INPUT VOLTAGE [V] VFB =0.4V (not switching)
Quiescent Current vs. VIN (Switching)
2.0 SUPPLY CURRENT [mA]
1.5
1.0
0.5
0.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
FB pin voltage vs. Supply Voltage
315
FB Pin Voltage vs. Output Current
315 FB PIN VOLTAGE [mV]
310 FEEDBACK [mV] 305 300 295 290 285 2.7 3.0
8LEDs at 20mA VOUT= 26V
310 8 LEDs 305 300 295 290 285
3.3 3.6 3.9 4.2 4.5 INPUT VOLTAGE [V]
4.8
0
5 10 15 20 25 OUTPUT CURRENT [mA]
30
Switching Frequency vs. Supply Voltage
1040
Switching Waveforms
1020 FREQUENCY [kHz]
1000
980
960 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 INPUT VOLTAGE [V]
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
5
Doc. No. MD-5013, Rev. B
CAT4237
TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7F, COUT = 0.22F, L = 33H with 8 LEDs at 20mA, TAMB = 25C, unless otherwise specified. LED Current vs. Input Voltage (8 LEDS)
35
LED Current Regulation (20mA)
1.0% CURRENT VARIATION [%] .
30 LED CURRENT [mA] 25 20 15 10 5 0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0 RFB = 20 RFB = 10 RFB = 15
0.5%
0.0%
-0.5%
-1.0% 3.0 3.3 3.6 3.9 4.2 4.5 INPUT VOLTAGE [V] 4.8
8 LED Efficiency vs. Load Current
90 VIN = 4.2V EFFICIENCY [%]
EFFICIENCY [%] 90
8 LED Efficiency vs. Input Voltage
20mA 85 80 75 70 65 8 LEDs VOUT ~ 27V at 20mA L = 33uH 3.0 3.5 4.0 4.5 5.0 15mA
85 80 75 70 65 5 10 15 20 25 30 LED CURRENT [mA] 8 LEDs VOUT ~ 27V at 20mA L = 33uH VIN = 3.6V
INPUT VOLTAGE [V]
7 LED Efficiency vs. Load Current
90 85 VIN = 3.6V 80 75 70 65 5 10 15 20 25 30 LED CURRENT [mA]
Doc. No. MD-5013, Rev. B
6 LED Efficiency vs. Load Current
90 85 VIN = 3.6V 80 75 70 65 5 10 15 20 25 30 LED CURRENT [mA]
6
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
VIN = 4.2V
VIN = 4.2V
EFFICIENCY [%]
7 LEDs VOUT ~ 23V at 20mA L = 33uH
EFFICIENCY [%]
6 LEDs VOUT ~ 20V at 20mA L = 33uH
CAT4237
TYPICAL CHARACTERISTICS VIN = 3.6V, CIN = 4.7F, COUT = 0.22F, L = 33H with 8 LEDs at 20mA, TAMB = 25C, unless otherwise specified. Power-up with 8 LEDs at 20mA
SWITCH RESISTANCE [ohm]
Switch ON Resistance vs. Input Voltage
2.0
1.5
1.0
0.5
0.0 2.5 3.0 3.5 4.0 INPUT VOLTAGE [V] 4.5
FB pin voltage vs. Temperature
303 FEEDBACK VOLTAGE [mV]
SHUTDOWN VOLTAGE [V]
Shutdown Voltage vs. Input Voltage
1.0 25C -40C
302 301 300 299 298 297 -50 0 50 100 150 TEMPERATURE [C] V IN =3.6V, 8LEDs ILED =20mA
0.8
0.6
125 C
0.4 85C
0.2 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0
Maximum Output Current vs. Input Voltage
140 MAX OUTPUT CURRENT [mA] 120 100 80 60 40 20 0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] 5.0 VOUT = 20V VOUT = 15V
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
7
Doc. No. MD-5013, Rev. B
CAT4237 APPLICATION INFORMATION
External Component Selection Capacitors The CAT4237 only requires small ceramic capacitors of 4.7F on the input and 0.22F on the output. Under normal condition, a 4.7F input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 10F may be appropriate. X5R and X7R capacitor types are ideal due to their stability across temperature range. Inductor A 33H inductor is recommended for most of the CAT4237 applications. In cases where the efficiency is critical, inductances with lower series resistance are preferred. Inductors with current rating of 300mA or higher are recommended for most applications. Sumida CDRH3D16-330 33H inductor has a rated current of 320mA and a series resistance (D.C.R.) of 520m typical. Schottky Diode The current rating of the Schottky diode must exceed the peak current flowing through it. The Schottky diode performance is rated in terms of its forward voltage at a given current. In order to achieve the best efficiency, this forward voltage should be as low as possible. The response time is also critical since the driver is operating at 1MHz. Central Semiconductor Schottky diode CMDSH05-4 (500mA rated) is recom- mended for most applications. LED Current Setting The LED current is set by the external resistor R1 connected between the feedback pin (FB) and ground. The formula below gives the relationship between the resistor and the current: R1 = 0.3V/LED current Table 1. Resistor R1 and LED current LED current (mA) 5 10 15 20 25 30 R1 () 60 30 20 15 12 10
Doc. No. MD-5013, Rev. B
8
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
CAT4237 OPEN LED PROTECTION
In the event of an "Open LED" fault condition, the CAT4237 will continue to boost the output voltage with maximum power until the output voltage reaches approximately 35V. Once the output exceeds this level, the internal circuitry immediately places the device into a very low power mode where the total input power is limited to about 4mW (about 1mA input current with a 3.6V supply). The SW pin clamps at a voltage below its maximum rating of 60V. There is no need to use an external zener diode between Vout and the FB pin. A 50V rated C2 capacitor is required to prevent any overvoltage damage in the open LED condition.
Open LED Protection without Zener
L VIN C1 4.7F VIN SW 33H C2 0.22F Schottky 100V (Central CMSH1-100) VOUT
Open LED Switching waveforms without Zener
CAT4237 OFF ON SHDN GND FB VFB = 300mV R1 15
Open LED Supply Current vs. VIN without Zener
2.0 SUPPLY CURRENT [mA]
OUTPUT VOLTAGE [V]
Open LED Output Voltage vs. VIN without Zener
50
1.5
45
1.0
40
0.5
35
0.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
30 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V]
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
9
Doc. No. MD-5013, Rev. B
CAT4237 DIMMING CONTROL
There are several methods available to control the LED brightness. PWM signal on the SHDN Pin LED brightness dimming can be done by applying a PWM signal to the SHDN input. The LED current is repetitively turned on and off, so that the average current is proportional to the duty cycle. A 100% duty cycle, with SHDN always high, corresponds to the LEDs at nominal current. Figure 1 shows a 1kHz signal with a 50% duty cycle applied to the SHDN pin. The recommended PWM frequency range is from 100Hz to 2kHz. Filtered PWM Signal A filtered PWM signal used as a variable DC voltage can control the LED current. Figure 2 shows the PWM control circuitry connected to the CAT4237 FB pin. The PWM signal has a voltage swing of 0V to 2.5V. The LED current can be dimmed within a range from 0mA to 20mA. The PWM signal frequency can vary from very low frequency up to 100kHz.
VIN SW
CAT4237 SHDN GND 2.5V 0V 3.73k VIN RA C1 RB i R2 3.1k FB VFB = 300mV 1k
PWN Signal
LED Current R1 15
0.22F
Figure 2. Circuit for Filtered PWM Signal A PWM signal at 0V DC, or a 0% duty cycle, results in a max LED current of about 22mA. A PWM signal with a 93% duty cycle or more, results in an LED current of 0mA.
FILTERED PWM DIMMING [0V to 2.5V]
Figure 1. Switching Waveform with 1kHz PWM on SHDN
LED CURRENT [mA]
25 20 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 PWM DUTY CYCLE [%]
Doc. No. MD-5013, Rev. B
10
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
CAT4237 BOARD LAYOUT
The CAT4237 is a high-frequency switching regulator. The traces that carry the high-frequency switching current have to be carefully layout on the board in order to minimize EMI, ripple and noise in general. The thicker lines on Figure 3 show the switching current path. All these traces have to be short and wide enough to minimize the parasitic inductance and resistance. The loop shown on Figure 3 corresponds to the current path when the CAT4237 internal switch is closed. On Figure 4 is shown the current loop, when the CAT4237 switch is open. Both loop areas should be as small as possible. Capacitor C1 has to be placed as close as possible to the VIN pin and GND. The capacitor C2 has to be connected separately to the top LED anode. A ground plane under the CAT4237 allows for direct connection of the capacitors to ground. The resistor R1 must be connected directly to the GND pin of the CAT4237 and not shared with the switching current loops and any other components.
closed
open
Figure 3. Closed-switch Current Loop
Figure 4. Open-switch Current Loop
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
11
Doc. No. MD-5013, Rev. B
CAT4237 PACKAGE OUTLINES 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-229.
Doc. No. MD-5013, Rev. B
12
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
CAT4237 EXAMPLE OF ORDERING INFORMATION 1
Prefix CAT Device # 4237 Suffix TD - G T3
Product Number 4237 Optional Company ID Package TD: TSOT-23
Lead Finish G: NiPdAu Blank: Matte-Tin(4)
Tape & Reel T: Tape & Reel 3: 3000/Reel
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 CAT4237TD-GT3 (TSOT-23, NiPdAu Plated Finish, Tape & Reel 3000). (4) For Matte-Tin package option, please contact your nearest Catalyst Semiconductor Sales office.
Doc. No. MD-5013, Rev. B
13
(c) Catalyst Semiconductor, Inc. Characteristics subject to change without notice
REVISION HISTORY
Date 12/13/2005 01/31/2007 Rev. 00 A Reason Initial Issue Update Absolute Maximum Ratings Update Recommended Operating Conditions Change document number from 25094 to 5013, Rev. A Add NiPdAu lead finish Add Extended Temperature range Update Package Outline Drawing Add Example of Ordering Information Add "MD-" to Document Number
01/07/2008
B
Copyrights, Trademarks and Patents (c) Catalyst Semiconductor, Inc. Trademarks and registered trademarks of Catalyst Semiconductor include each of the following: Adaptive AnalogTM, Beyond MemoryTM, DPPTM, EZDimTM, LDDTM, MiniPotTM, Quad-ModeTM and Quantum Charge ProgrammableTM Catalyst Semiconductor has been issued U.S. and foreign patents and has patent applications pending that protect its products. CATALYST SEMICONDUCTOR MAKES NO WARRANTY, REPRESENTATION OR GUARANTEE, EXPRESS OR IMPLIED, REGARDING THE SUITABILITY OF ITS PRODUCTS FOR ANY PARTICULAR PURPOSE, NOR THAT THE USE OF ITS PRODUCTS WILL NOT INFRINGE ITS INTELLECTUAL PROPERTY RIGHTS OR THE RIGHTS OF THIRD PARTIES WITH RESPECT TO ANY PARTICULAR USE OR APPLICATION AND SPECIFICALLY DISCLAIMS ANY AND ALL LIABILITY ARISING OUT OF ANY SUCH USE OR APPLICATION, INCLUDING BUT NOT LIMITED TO, CONSEQUENTIAL OR INCIDENTAL DAMAGES. Catalyst Semiconductor 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 Catalyst Semiconductor product could create a situation where personal injury or death may occur. Catalyst Semiconductor reserves the right to make changes to or discontinue any product or service described herein without notice. Products with data sheets labeled "Advance Information" or "Preliminary" and other products described herein may not be in production or offered for sale. Catalyst Semiconductor advises customers to obtain the current version of the relevant product information before placing orders. Circuit diagrams illustrate typical semiconductor applications and may not be complete.
Catalyst Semiconductor, Inc. Corporate Headquarters 2975 Stender Way Santa Clara, CA 95054 Phone: 408.542.1000 Fax: 408.542.1200 2Hwww.catsemi.com
Document No: MD-5013 Revision: B Issue date: 01/07/08

▲Up To Search▲

Price & Availability of CAT4237TD-GT3

	To Download CAT4237TD-GT3 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .