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CAT4101TV-T75 Datasheet(PDF) 8 Page - ON Semiconductor |
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CAT4101TV-T75 Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 11 page CAT4101 Doc. No. MD-5036, Rev. D 8 © 2009 SCILLC. All rights reserved. Characteristics subject to change without notice APPLICATION INFORMATION SINGLE 12 V SUPPLY The circuit shown in Figure 3 shows how to power three LEDs in series from a single 12 V supply using the CAT4101. The CAT4101 can not be driven directly from 12 V, three components are needed to create a lower voltage for the VIN pin (below 5.5 V). Resistor R2 and zener diode D provide a regulated voltage while the quiescent current runs through the N-Channel transistor M. Suitable parts for this circuit are the ON Semiconductor MM3Z6V2 zener diode and the 2N7002L N-channel transistor (SOT23 package). Figure 3. Single Supply Driving Three LEDs POWER DISSIPATION The power dissipation (PD) of the CAT4101 can be calculated as follows: () ( ) LED LED IN IN D I V I V P × + × = where VLED is the voltage at the LED pin. Combinations of high VLED voltage or high ambient temperature can cause the CAT4101 to enter thermal shutdown. In applications where VLED is high, a resistor can be inserted in series with the LED string to lower PD. Thermal dissipation of the junction heat consists primarily of two paths in series. The first path is the junction to the case ( θ JC) thermal resistance which is defined by the package style, and the second path is the case to ambient ( θ CA) thermal resistance, which is dependent on board layout. The overall junction to ambient ( θ JA) thermal resistance is equal to: θ JA = θJC + θCA For a given package style and board layout, the operating junction temperature TJ is a function of the power dissipation PD, and the ambient temperature, resulting in the following equation: TJ = TAMB + PD (θJC + θCA) = TAMB + PD θJA The CAT4101 TO-263 5-lead package provides a thermal resistance when the ground tab is soldered down to the PCB. When mounted on a double-sided printed circuit board with two square inches of copper allocated for “heat spreading”, the resulting θ JA is about 30°C/W. For example, at 60°C ambient temperature, the maximum power dissipation is calculated as follow: W 3 30 60 150 T T P JA AMB Jmax Dmax = = θ = - - RECOMMENDED LAYOUT The board layout should provide good thermal dissipation through the PCB. Multiple via can be used to connect the tab of the CAT4101 to a large ground plane underneath the package. Input capacitor C1 should be placed as close to the driver IC as possible. The RSET resistor should have a Kelvin connection to the GND pin of the CAT4101. Figure 4. CAT4101 Recommended Layout VIN R2 5 k Ω D 6.2 V M CAT4101 12 V R1 C1 0.1 µF EN/PWM RSET LED GND C2 1 µF |
Similar Part No. - CAT4101TV-T75 |
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Similar Description - CAT4101TV-T75 |
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