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LT3508HFE-TRPBF 数据表(PDF) 18 Page - Linear Technology |
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LT3508HFE-TRPBF 数据表(HTML) 18 Page - Linear Technology |
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18 / 24 page  LT3508 18 3508fb applications or in battery back-up systems where a battery or some other supply is diode OR-ed with the LT3508’s output. If the VIN pin is allowed to float and the SHDN pin is held high (either by a logic signal or because it is tied to VIN), then the LT3508’s internal circuitry will pull its quiescent current through its SW pin. This is fine if your system can tolerate a few mA in this state. If you ground the SHDN pin, the SW pin current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LT3508 can pull large currents from the output through the SW pin and the VIN pin. Figure 10 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. APPLICATIONS INFORMATION Figure 11. A Good PCB Layout Ensures Proper Low EMI Operation PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 11 shows the recommended PCB layout with trace and via locations. Note that large, switched currents flow in the LT3508’s VIN and SW pins, the catch diode (D1) and the input capacitor (CIN). The loop formed by these components should be as small as possible. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane below these components. The SW and BOOST nodes should be as small as possible. Finally, keep the FB and VC nodes small so that the ground traces will shield them from the SW and BOOST nodes. The Exposed Pad on the bottom of the package must be soldered to ground so that the pad acts as a heat sink. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT3508 to additional ground planes within the circuit board and on the bottom side. VIN VIN VOUT SW LT3508 D4 PARASITIC DIODE 3508 F10 Figure 10. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output (11a) Example Layout for FE16 Package (11b) Example Layout for QFN Package |
类似零件编号 - LT3508HFE-TRPBF |
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类似说明 - LT3508HFE-TRPBF |
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