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CAT3648HV3-GT2 Datasheet(PDF) 11 Page - Catalyst Semiconductor |
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CAT3648HV3-GT2 Datasheet(HTML) 11 Page - Catalyst Semiconductor |
11 / 14 page CAT3648 © Catalyst Semiconductor, Inc. 11 Doc. No. MD-5031, Rev. A Characteristics subject to change without notice Unused LED Channels For applications not requiring all the channels, it is recommended the unused LED pins be tied directly to VOUT (see Figure 4). Figure 4. Application with 3 LEDs Protection Mode If an LED is disconnected, the driver senses that and automatically ignores that channel. When all LEDs are disconnected, the driver goes to 1x mode where the output is equal to the input voltage. As soon as the output exceeds about 6V, the driver resets itself and re-evaluates the mode. If the die temperature exceeds +150°C, the driver will enter a thermal protection shutdown mode. When the device temperature drops by about 20°C, the device will resume normal operation. LED Selection LEDs with forward voltages (VF) ranging from 1.3V to 4.3V may be used. Selecting LEDs with lower VF is recommended in order to improve the efficiency by keeping the driver in 1x mode longer as the battery voltage decreases. For example, if a white LED with a VF of 3.3V is selected over one with VF of 3.5V, the driver will stay in 1x mode for lower supply voltage of 0.2V. This helps improve the efficiency and extends battery life. External Components The driver requires four external 1μF ceramic capa- citors for decoupling input, output, and for the charge pump. Both capacitors type X5R and X7R are recommended for the LED driver application. In all charge pump modes, the input current ripple is kept very low by design and an input bypass capacitor of 1μF is sufficient. In 1x mode, the device operates in linear mode and does not introduce switching noise back onto the supply. Recommended Layout In charge pump mode, the driver switches internally at a high frequency. It is recommended to minimize trace length to all four capacitors. A ground plane should cover the area under the driver IC as well as the bypass capacitors. Short connection to ground on capacitors CIN and COUT can be implemented with the use of multiple via. A copper area matching the TQFN exposed pad (TAB) must be connected to the ground plane underneath. The use of multiple via improves the package heat dissipation. Figure 5. Recommended Layout VIN GND Pin1 C2 C1 RSET CIN COUT GND GND EN/DIM GND VIN LED2 LED3 LED1 LED4 RSET EN/DIM CAT3648 VIN VOUT 1µF 1µF CIN C1- C1+ C2- C2+ 1µF 1µF COUT RSET ENABLE DIMMING |
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