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LT1765 Datasheet(PDF) 6 Page - Linear Technology |
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LT1765 Datasheet(HTML) 6 Page - Linear Technology |
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6 / 20 page  LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 6 1765fd PIN FUNCTIONS FB: The feedback pin is used to set output voltage using an external voltage divider (adjustable version) that gener- ates 1.2V at the pin when connected to the desired output voltage. The fixed voltage 1.8V, 2.5V, 3.3V and 5V versions have the divider network included internally and the FB pin is connected directly to the output. If required, the current limit can be reduced during start up or short-circuit when the FB pin is below 0.5V (see the Current Limit Foldback graph in the Typical Performance Characteristics section). An impedance of less than 5kΩ on the adjustable version at the FB pin is needed for this feature to operate. BOOST: The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. VIN: This is the collector of the on-chip power NPN switch. This pin powers the internal circuitry and internal regulator. At NPN switch on and off, high di/dt edges occur on this pin. Keep the external bypass capacitor and catch diode close to this pin. All trace inductance on this path will create a voltage spike at switch off, adding to the VCE volt- age across the internal NPN. Both VIN pins of the TSSOP package must be shorted together on the PC board. GND: The GND pin acts as the reference for the regulated output, so load regulation will suffer if the “ground” end of the load is not at the same voltage as the GND pin of the IC. This condition will occur when load current or other currents flow through metal paths between the GND pin and the load ground point. Keep the ground path short between the GND pin and the load and use a ground plane when possible. Keep the path between the input bypass and the GND pin short. The exposed GND pad and/or GND pins of the package are directly attached to the internal tab. These pins/pad should be attached to a large copper area to reduce thermal resistance. VSW: The switch pin is the emitter of the on-chip power NPN switch. This pin is driven up to the input pin voltage during switch on time. Inductor current drives the switch pin negative during switch off time. Negative voltage must be clamped with an external catch diode with a VBR <0.8V. Both VSW pins of the TSSOP package must be shorted together on the PC board. SYNC: The sync pin is used to synchronize the internal oscillator to an external signal. It is directly logic compat- ible and can be driven with any signal between 20% and 80% duty cycle. The synchronizing range is from 1.6MHz to 2MHz. See Synchronization section in Applications Information for details. When not in use, this pin should be grounded. SHDN: The shutdown pin is used to turn off the regula- tor and to reduce input drain current to a few microam- peres. The 1.33V threshold can function as an accurate undervoltage lockout (UVLO), preventing the regulator from operating until the input voltage has reached a pre- determined level. Float or pull high to put the regulator in the operating mode. VC: The VC pin is the output of the error amplifier and the input of the peak switch current comparator. It is normally used for frequency compensation, but can do double duty as a current clamp or control loop override. This pin sits at about 0.4V for very light loads and 0.9V at maximum load. It can be driven to ground to shut off the output. |
Similar Part No. - LT1765_15 |
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Similar Description - LT1765_15 |
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