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CAT3616HV4 Datasheet(PDF) 10 Page - Catalyst Semiconductor |
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CAT3616HV4 Datasheet(HTML) 10 Page - Catalyst Semiconductor |
10 / 14 page CAT3616 Doc. No. 5018 Rev. A 10 © 2006 Catalyst Semiconductor, Inc. Characteristics subject to change without notice LED CURRENT SETTING The LED current is controlled by toggling the input signals ENM ¯¯¯ and ENS ¯¯¯. ENM ¯¯¯ controls the four LED channels MAIN1 to MAIN4. ENS ¯¯¯ controls the two LED lines SUB1 and SUB2. ENM ¯¯¯ and ENS ¯¯¯ work the same way. The chip must first be enabled by setting the enable input EN high. On the first ENM ¯¯¯ or ENS ¯¯¯ transition from high to low, the LED current in the associated LEDs is set to the full scale 31mA. On each consecutive falling edge of ENM ¯¯¯ or ENS ¯¯¯, the LED current is decreased by 1mA. On the 32 nd pulse, the LED channel is turned off and the current drops to 0mA. One additional ENM ¯¯¯ or ENS ¯¯¯ pulse resets the full current to 31mA, as shown on Figure 1. Consecutive pulses should be separated by 300ns or more. Pulsing frequencies from 5kHz up to 1MHz are supported during dimming operations. When the EN is held low for 1.5ms or more, the CAT3616 enters the shutdown mode and draws “zero” current. When the enable EN input is low, toggling ENM ¯¯¯ or ENS ¯¯¯ has no effect. Unused LED channels can be disabled independently by connecting the corresponding main or sub LED pin to VOUT. Protection Mode If an LED becomes open-circuit, the output voltage VOUT is internally limited to about 5.5V. This is to prevent the output pin from exceeding its absolute maximum rating. The driver enters a thermal shutdown mode as soon as the die temperature exceeds about +165ºC. When the device temperature drops down by about 20ºC, the device resumes normal operation. External Components The driver requires a total of four external 1 µF ceramic capacitors: two for decoupling input and output, and two for the charge pump. Both capacitor types X5R and X7R are recommended for the LED driver application. In the 1.5x charge pump mode, the input current ripple is kept very low by design, and an input bypass capacitor of 1 µF is sufficient. In 1x mode, the device operating in linear mode does not introduce switching noise back onto the supply. Recommended Layout In 1.5x charge pump mode, the driver switches internally at a high frequency of 1MHz. 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 TDFN exposed pad (GND) must be connected to the ground plane underneath. The use of multiple via improves the package heat dissipation. |
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