Datasheet LT3663 (Analog Devices) - 7

LT3663
operaTion (Refer to Block Diagram)
The LT3663 is a constant frequency, current mode step This al ows the driver to ful y saturate the internal bipolar down regulator. A switch cycle is initiated when the os- NPN power switch for efficient operation. The switch driver cil ator enables the RS flip flop, turning on the internal operates from either VIN or BOOST to ensure startup. power switch, Q1. The sense amplifier (A1) monitors the An internal regulator provides power to the control circuitry. switch current via the voltage dropped across the current This regulator includes input undervoltage and overvoltage sense resistor RSENSE1. The comparator compares the protection which disables switching action when V amplified current signal with the output (V IN is C) of the error out of range. When switching is disabled, the LT3663 amplifier (G1). The switch is turned off when this current safely sustains input voltages up to 60V. Note that while exceeds a value determined by the VC voltage. The error switching is disabled the output will discharge. amplifier monitors the VOUT voltage through an internal resistor divider and, when not driven external y, servos Output current limiting is provided via the servo action of the VC voltage to regulate VOUT. If the VOUT voltage drops, amplifier G2. The voltage across sense resistor, RSENSE2, the VC voltage will be driven higher increasing the output is compared to a voltage programmed by external resistor current and VOUT voltage. An active clamp (not shown) RILIM on the ILIM pin. A capacitor averages the inductor on the VC node provides current limit. The LT3663 is ripple current. If the average inductor current exceeds the internal y compensated with a pole-zero combination on programmed value then the VC voltage is pul ed low, reduc- the VC node. ing the current in the regulator. The output current limit circuit al ows for a lower current rated inductor and diode An external capacitor and internal diode, D2, generate a and provides better control of system power dissipation. voltage at the BOOST pin that is higher than the input supply. 3663fc For more information For more information www.linear.com/LT3663 7 Document Outline Description Typical Application Absolute Maximum Ratings Electrical Characteristics Typical Performance Characteristics Operation Applications Information Package Description