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LT1085CM-3.6 Datasheet(PDF) 8 Page - Linear Technology |
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LT1085CM-3.6 Datasheet(HTML) 8 Page - Linear Technology |
8 / 12 page 8 LT1083/LT1084/LT1085 Fixed 1083ffd up into very heavy loads. During the start-up, as the input voltage is rising, the input-to-output voltage differential remains small allowing the regulator to supply large output currents. With high input voltage a problem can occur wherein removal of an output short will not allow the output voltage to recover. Older regulators such as the 7800 series, also exhibited this phenomenon so it is not unique to the LT1083. The problem occurs with a heavy output load when the input voltage is high and the output voltage is low, such as immediately after a removal of a short. The load line for such a load may intersect the output current curve at two points. If this happens there are two stable output operat- ing points for the regulator. With this double intersection the power supply may need to be cycled down to zero and brought up again to make the output recover. Ripple Rejection In applications that require improved ripple rejection the LT1083 series adjustable regulators should be used. With LT1083 series adjustable regulators the addition of a bypass capacitor from the adjust pin to ground will reduce output ripple by the ratio of VOUT/1.25V. See LT1083 series adjustable regulator data sheet. Load Regulation Because the LT1083 is a three-terminal device, it is not possible to provide true remote load sensing. Load regu- lation will not be limited by the resistance of the wire connecting the regulator to the load. The data sheet specification for the load regulation is measured at the bottom of the package. Negative side sensing is a true Kelvin connection, with the ground pin of the device returned to the negative side of the load. Thermal Considerations The LT1083 series of regulators have internal power and thermal limiting circuitry designed to protect the device under overload conditions. For continuous normal load conditions however, maximum junction temperature rat- ings must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. This includes junction-to-case, folded back as input-to-output voltage increases. This negative resistance can react with capacitors or inductors on the input to cause oscillations during current limiting. Depending on the value of series resistance, the overall circuitry may end up unstable. Since this is a system problem, it is not necessarily easy to solve; however it does not cause any problems with the IC regulator and can usually be ignored. Protection Diodes In normal operation the LT1083 family does not need any protection diodes, The internal diode between the input and the output pins of the LT1083 family can handle microsecond surge currents of 50A to 100A. Even with large output capacitances it is very difficult to get those values of surge current in normal operation. Only with high value output capacitors, such as 1000 μF to 5000μF and with the input pin instantaneously shorted to ground, can damage occur. A crowbar circuit at the input of the LT1083 can generate those kinds of currents and a diode from output-to-input is then recommended. Normal power sup- ply cycling or even plugging and unplugging in the system will not generate currents large enough to do any damage. IN OUT ADJ VOUT LT1083 D1 1N4002 (OPTIONAL) VIN 1083/4/5 AI01 COUT 150 μF + Overload Recovery Like any of the IC power regulators, the LT1083 has safe area protection. The safe area protection decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. The LT1083 protection is designed to provide some output current at all values of input-to-output voltage up to the device breakdown. When power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to start APPLICATIO S I FOR ATIO |
Similar Part No. - LT1085CM-3.6 |
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Similar Description - LT1085CM-3.6 |
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