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LT8580 Datasheet(PDF) 9 Page - Linear Technology |
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LT8580 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 32 page  LT8580 9 8580f For more information www.linear.com/LT8580 Start-Up Operation Several functions are provided to enable a very clean start-up for the LT8580. • First, the SHDN pin voltage is monitored by an internal voltage reference to give a precise turn-on voltage level. Anexternalresistor(orresistordivider)canbeconnected from the input power supply to the SHDN pin to provide a user-programmable undervoltage lockout function. • Second, the soft-start circuitry provides for a gradual ramp-up of the switch current. When the part is brought out of shutdown, the external SS capacitor is first discharged (providing protection against SHDN pin glitches and slow ramping), then an integrated 280k resistor pulls the SS pin up to ~2.1V. By connecting an external capacitor to the SS pin, the voltage ramp rate on the pin can be set. Typical values for the soft-start capacitor range from 100nF to 1µF. • Finally,thefrequencyfoldbackcircuitreducestheswitch- ing frequency when the FBX pin is in a nominal range of 300mV to 920mV. This feature reduces the minimum duty cycle that the part can achieve thus allowing better control of the switch current during start-up. When the FBX voltage is pulled outside of this range, the switching frequency returns to normal. Current Limit and Thermal Shutdown Operation The LT8580 has a current limit circuit not shown in the BlockDiagram.Theswitchcurrentisconstantlymonitored and not allowed to exceed the maximum switch current at a given duty cycle (see the Electrical Characteristics table). If the switch current reaches this value, the SR latch (SR1) is reset regardless of the state of the comparator (A1/ A2). Also, not shown in the Block Diagram is the thermal shutdown circuit. If the temperature of the part exceeds approximately165°C,theSR2latchissetregardlessofthe state of the amplifier (A1/A2). When the part temperature falls below approximately 160°C, a full soft-start cycle will then be initiated. The current limit and thermal shutdown circuits protect the power switch as well as the external components connected to the LT8580. operaTion |
Similar Part No. - LT8580_15 |
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Similar Description - LT8580_15 |
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