link to page 10 link to page 10 link to page 10 link to page 11 CAT4201 300 Operation from High Supply Voltage Above 14 V For operation from a supply voltage above 14 V, it is 250 recommended to have a slew rate of 1 ms or more for every 5 V increase in VBAT supply. When using a high supply [mA] 200 voltage of 24 V, a 1 W or 2 W resistor in series with the supply, as shown on Figure 28, is recommended to limit the slew rate 150 of the supply voltage. A 4.7 mF minimum ceramic capacitor is placed between the VBAT pin and ground. The 100 combination of the series resistor R3 and input capacitor C1 LED CURRENT acts as a low pass filter limiting the excessive in−rush 50 currents and overvoltage transients which would otherwise occur during “hot−plug” conditions, thereby protecting the 0 CAT4201 driver. 100 80 60 40 20 0 DUTY CYCLE [%] VBAT R3 Figure 25. LED Current vs. Duty Cycle 24 V C1 1 W VBAT 4.7 mF D1 C2 VBAT 12 V C1 CAT4201 4.7 mF RSET 4.7 mF R1 D C2 L VBAT 10 kW CTRL SW 300 mA GND 33 mH CAT4201 10 mF RSET R1 R1 L 10 kW CTRL SW 1 kW GND 22 mH Q1 Figure 28. 24 V Application with 5 LEDs R2 PWM NPN control 5 V R4 Operation from High Supply Voltage of 36 V 1 kW 0 V When powering from a high supply voltage of 36 V, a 2 W 1 kW R5 resistor in series with the supply is recommended, as shown 47 kW on Figure 29, to limit the slew rate of the supply voltage. Inductor value should be 33 mH or higher. Figure 26. Circuit for PWM on CTRL VBAT R3 PWM on RSET Pin 36 V C1 Another dimming method is to place in parallel to R1 2 W another resistor with a FET in series, as shown on Figure 27. 4.7 mF D1 C2 R1 sets the minimum LED current corresponding to 0% duty VBAT CAT4201 cycle. The combined resistor of R1 and Rmax sets the 2.2 mF RSET maximum LED current corresponding to 100% duty cycle. R1 L 10 kW CTRL SW 300 mA VBAT GND 47 mH 13 V C1 R2 4.7 mF D C2 1 kW VBAT Figure 29. 36 V Application with 6 LEDsCAT4201 10 mF RSET Parallel Configuration for Driving LEDs Beyond Rmax R1 L CTRL SW 350 mA GND 22 mH Several CAT4201 devices can be connected in parallel for Q1 PWM R2 driving LEDs with current in excess of 350 mA. The NPN control CAT4201 driver circuits are connected to the same LED 1 kW OFF ON cathode. Figure 30 shows the application schematic for driving 1 A into one LED with three CAT4201 connected in Figure 27. Circuit for PWM on RSET parallel. Each CAT4201 is driving the LED with a current set A resistor value for R1 of less than 90 kW is recommended by its RSET resistor. The resulting LED current is equal to to provide better accuracy. the sum of each driver current. www.onsemi.com10
