cat4237 Catalyst Semiconductor, cat4237 Datasheet
cat4237
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cat4237 Summary of contents
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... Top View © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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 ...
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... CAT4237 ABSOLUTE MAXIMUM RATINGS Parameters voltage IN SHDN ¯¯¯¯¯ voltage SW voltage Storage Temperature Range Junction Temperature Range Lead Temperature RECOMMENDED OPERATING CONDITIONS Typical application circuit with external components are shown on page 1. Parameters pin voltage Ambient Temperature Range ...
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... LED current according to the formula: The lower LED cathode is connected to the FB pin. 33µH 1MHz Over Voltage Oscillator – – – Current Sense 3 CAT4237 I = 0.3V/R LED 0.22µF Protection Driver LED PWM & Current Logic GND FB 15Ω ...
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... 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 ). ...
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... Catalyst Semiconductor, Inc. Characteristics subject to change without notice Quiescent Current vs. V 2.0 1.5 1.0 0.5 0.0 2.5 4.2 4.5 4.8 FB Pin Voltage vs. Output Current 315 310 305 300 295 290 285 4.2 4.5 4.8 4.5 4.8 5 CAT4237 = 25ºC, unless otherwise specified. AMB (Switching) IN 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V] 8 LEDs OUTPUT CURRENT [mA] Switching Waveforms Doc. No. MD-5013, Rev. B ...
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... CAT4237 TYPICAL CHARACTERISTICS V = 3.6V 4.7μ 0.22µ 33µH with 8 LEDs at 20mA OUT LED Current vs. Input Voltage (8 LEDS Ω Ω 2.5 3.0 3.5 4.0 INPUT VOLTAGE [V] 8 LED Efficiency vs. Load Current 90 VIN = 4. VIN = 3. LEDs 70 VOUT ~ 27V at 20mA ...
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... INPUT VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice Switch ON Resistance vs. Input Voltage 2.0 1.5 1.0 0.5 0.0 2.5 Shutdown Voltage vs. Input Voltage 1.0 0.8 0.6 0.4 0.2 100 150 3.0 4.5 5.0 7 CAT4237 = 25ºC, unless otherwise specified. AMB 3.0 3.5 4.0 4.5 INPUT VOLTAGE [V] -40°C 25°C 125° C 85°C 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V] Doc. No. MD-5013, Rev. B ...
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... X7R capacitor types are ideal due to their stability across temperature range. Inductor A 33µH 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. ...
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... 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 ...
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... 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 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. ¯ ...
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... IN connected separately to the top LED anode. A ground plane under the CAT4237 allows for direct connection of the capacitors to ground. The resistor R connected directly to the GND pin of the CAT4237 and not shared with the switching current loops and any other components. open Figure 4. Open-switch Current Loop ...
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... CAT4237 PACKAGE OUTLINES DRAWING (1)(2) TSOT-23 5-Lead (TD TOP VIEW SIDE 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 SYMBOL A A1 ...
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... 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 ...
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... 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. ...