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LT1767 Datasheet(PDF) 6 Page - Linear Technology |
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LT1767 Datasheet(HTML) 6 Page - Linear Technology |
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6 / 20 page  LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 6 1767fb For more information www.linear.com/LT1767 pin FuncTions FB: The feedback pin is used to set output voltage using an external voltage divider that generates 1.2V at the pin with the desired output voltage. The fixed voltage 1.8V, 2.5V, 3.3V and 5V versions have the divider network in- cluded 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 (adjustable part only) 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. Without this added voltage, the typical switch voltage loss would be about 1.5V. The additional boost voltage allows the switch to saturate and voltage loss approximates that of a 0.22Ω FET structure. VIN: This is the collector of the on-chip power NPN switch. This pin powers the internal circuitry and internal regu- lator. 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 in this path will create a voltage spike at switch off, adding to the VCE voltage across the internal NPN. 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 GND pin of the MS8 package is directly attached to the internal tab. This pin should be attached to a large copper area to improve thermal resistance. The exposed pad of the MS8E package is also connected to GND. This should be soldered to a large copper area to improve its 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. 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 equal to initial operating frequency, up to 2MHz. See Synchronization in Applications Information section for details. When not in use, this pin should be grounded. SHDN:Theshutdownpinisusedtoturnofftheregulatorand to reduce input drain current to a few microamperes. The 1.33V threshold can function as an accurate undervoltage lockout (UVLO), preventing the regulator from operating until the input voltage has reached a predetermined level. Floatorpullhightoputtheregulatorintheoperatingmode. 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 0.35V for very light loads and 0.9V at maximum load. It can be driven to ground to shut off the output. |
Similar Part No. - LT1767_15 |
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Similar Description - LT1767_15 |
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