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CAT4109 Datasheet(PDF) 9 Page - ON Semiconductor |
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CAT4109 Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 10 page CAT4109, CAV4109 www.onsemi.com 9 Application Information Power Dissipation The power dissipation (PD) of the CAT4109/CAV4109 can be calculated as follows: PD + VDD IDD ) S VLEDN ILEDN where VLEDN is the voltage at the LED pin, and ILEDN is the associated LED current. Combinations of high VLED voltage or high ambient temperature can cause the CAT4109/CAV4109 to enter thermal shutdown. In applications where VLEDN 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 ( qJC) thermal resistance which is defined by the package style, and the second path is the case to ambient ( qCA) thermal resistance, which is dependent on board layout. The overall junction to ambient ( qJA) thermal resistance is equal to: qJA + qJC ) qCA 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 (qJC ) qCA) + TAMB ) PD qJA When mounted on a double−sided printed circuit board with two square inches of copper allocated for “heat spreading”, the resulting qJA is about 74°C/W. For example, at 60 °C ambient temperature, the maximum power dissipation is calculated as follow: PDmax + (TJmax * TAMB) qJA + (150 * 60) 74 + 1.2 W Recommended Layout Bypass capacitor C1 should be placed as close to the IC as possible. RSET resistors should be directly connected to the GND pin of the device. For better thermal dissipation, multiple via can be used to connect the GND pad to a large ground plane. It is also recommended to use large pads and traces on the PCB wherever possible to spread out the heat. The LEDs for this layout are driven from a separate supply (VLED+), but they can also be driven from the same supply connected to VDD. Figure 15. Recommended Layout |
Similar Part No. - CAT4109_15 |
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Similar Description - CAT4109_15 |
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