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LT1963AEST-1.8 数据表(PDF) 20 Page - Linear Technology |
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LT1963AEST-1.8 数据表(HTML) 20 Page - Linear Technology |
20 / 28 page LT1963A Series 20 1963afd APPLICATIONS INFORMATION The output of the LT1963A can be pulled below ground without damaging the device. If the input is left open circuit or grounded, the output can be pulled below ground by 20V. For fixed voltage versions, the output will act like a large resistor, typically 5k or higher, limiting current flow to typically less than 600μA. For adjustable versions, the output will act like an open circuit; no current will flow out of the pin. If the input is powered by a voltage source, the output will source the short-circuit current of the device and will protect itself by thermal limiting. In this case, grounding the SHDN pin will turn off the device and stop the output from sourcing the short-circuit current. The ADJ pin of the adjustable device can be pulled above or below ground by as much as 7V without damaging the device. If the input is left open circuit or grounded, the ADJ pin will act like an open circuit when pulled below ground and like a large resistor (typically 5k) in series with a diode when pulled above ground. In situations where the ADJ pin is connected to a resistor divider that would pull the ADJ pin above its 7V clamp volt- age if the output is pulled high, the ADJ pin input current must be limited to less than 5mA. For example, a resistor divider is used to provide a regulated 1.5V output from the 1.21V reference when the output is forced to 20V. The top resistor of the resistor divider must be chosen to limit the current into the ADJ pin to less than 5mA when the ADJ pin is at 7V. The 13V difference between OUT and ADJ pins divided by the 5mA maximum current into the ADJ pin yields a minimum top resistor value of 2.6k. Figure 12. Reverse Output Current OUTPUT VOLTAGE (V) 0 3.0 4.0 5.0 8 1963A F12 2.0 1.0 2.5 3.5 4.5 1.5 0.5 0 2 1 3 4 6 9 7 5 10 LT1963A VOUT = VADJ TJ = 25°C VIN = 0V CURRENT FLOWS INTO OUTPUT PIN LT1963A-2.5 VOUT = VFB LT1963A-3.3 VOUT = VFB LT1963A-1.8 VOUT = VFB LT1963A-1.5 VOUT = VFB In circuits where a backup battery is required, several different input/output conditions can occur. The output voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage, or is left open circuit. Current flow back into the output will follow the curve shown in Figure 12. When the IN pin of the LT1963A is forced below the OUT pin or the OUT pin is pulled above the IN pin, input cur- rent will typically drop to less than 2μA. This can happen if the input of the device is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or a second regulator circuit. The state of the SHDN pin will have no effect on the reverse output current when the output is pulled above the input. |
类似零件编号 - LT1963AEST-1.8 |
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类似说明 - LT1963AEST-1.8 |
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