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LD3986J1828R-E Arkusz danych(PDF) 8 Page - STMicroelectronics |
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LD3986J1828R-E Arkusz danych(HTML) 8 Page - STMicroelectronics |
8 / 12 page LD3986 SERIES 8/12 APPLICATION INFORMATION CURRENT LIMIT The device includes short-circuit protection. It includes a current limiter that controls the pass transistor’s gate voltage to limit the output current to about 600mA. THERMAL OVERLOAD PROTECTION The Thermal over load protection limits total power dissipation in the device. When the junction temperature (TJ) exceeds +160°C, the thermal sensor sends a signal to the shutdown logic, turning off the pass transistors and allowing the device to cool. The pass transistors turns on again after the device’s junction temperature typically cools by 20°C, resulting in a pulsed output during continuous thermal overload conditions. POWER DISSIPATION Maximum power dissipation of the device depends on the thermal resistance of the case and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipated by the device is: PD = IO (VI -VO) The maximum power dissipation is: PMAX = (TJMAX - TA) / RTH Where: TJMAX = +125°C TA is the ambient temperature RTH thermal resistance. The device’s pins perform the dual function of providing an electrical connection as well as channeling heat away from the die. Use wide circuit-board traces and large, solid copper polygons to improve power dissipation. Using multiple vias to buried ground planes further enhances thermal conductivity. INPUT CAPACITOR An input capacitance of ≈ 1µF is required between the LD3986 input pin and ground (the amount of the capacitance may be increased without limit). This capacitor must be located a distance of not more than 1cm from the input pin and returned to a clean analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input. Important: Tantalum capacitors can suffer catastrophic failures due to surge current when connected to a low impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be guaranteed by the manufacturer to have a surge current rating sufficient for the application. There are no requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will be ≈ 1µF over the entire operating temperature range. OUTPUT CAPACITOR The LD3986 is designed specifically to work with very small ceramic output capacitors, any ceramic capacitor (temperature characteristics X7R, X5R, Z5U or Y5V) in 1 to 22 µF range with 5m. to 500m. ESR range is suitable in the LD3986 application circuit. it may also be possible to use tantalum or film capacitors at the output, but these are not as attractive for reasons of size and cost. The output capacitor must meet the requirement for minimum amount of capacitance and also have an ESR (Equivalent Series Resistance) value which is within a stable range. NOISE BYPASS CAPACITOR Connecting a 0.01µF capacitor between the CBYP pin and ground significantly reduces noise on both regulator outputs. This cap is connected directly to a high impedance node in the band gap reference circuit. Any significant loading on this node will cause a change on the regulated output voltage. For this reason, DC leakage current through this pin must be kept as low as possible for best output voltage accuracy. The use of this 0.01µF bypass capacitor is strongly recommended to prevent overshoot on the output during start up. The types of capacitors best suited for the noise bypass capacitor are ceramic and film. High-quality ceramic capacitors with either NPO or COG dielectric typically have very low leakage. Polypropylene and polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low leakage current. Unlike many other LDO’s, addition of a noise reduction capacitor does not effect the transient response of the device. TURN-ON/OFF INPUT OPERATION Each LD3986 output is turned off by pulling the relevant EN pin low, and turned on by pulling it high. To assure proper operation, the signal |
Podobny numer części - LD3986J1828R-E |
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Podobny opis - LD3986J1828R-E |
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