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CAT4240 Datasheet(PDF) 6 Page - Catalyst Semiconductor |
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CAT4240 Datasheet(HTML) 6 Page - Catalyst Semiconductor |
6 / 14 page CAT4240 Doc. No. MD-5026 Rev. C 6 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 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 (4.7μF) 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 plane 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 over- voltage detection circuit is connected to the SW pin. When the voltage reaches 40V, 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 # Name Function 1 SW Switch pin. This is the drain of the internal power switch. 2 GND Ground pin. Connect the pin to the ground plane. 3 FB Feedback pin. Connect to the last LED cathode. 4 SHDN ¯¯¯¯¯ Shutdown pin (Logic Low). Set high to enable the driver. 5 VIN Power Supply input. SIMPLIFIED BLOCK DIAGRAM VIN VIN VOUT Current Sense Ref 300mV LED Current C1 RS SHDN Thermal Shutdown & UVLO 1MHz Oscillator Over Voltage Protection PWM & Logic Driver C2 GND SW FB R1 + – |
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Similar Description - CAT4240 |
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