Datasheet LT1616 (Analog Devices) - 5

LT1616
W BLOCK DIAGRA
V 5 IN INT REG 1 BOOST SHDN 4 AND UVLO Σ SLOPE R COMP Q S Q DRIVER Q1 OSC 6 SW FREQUENCY VC FOLDBACK gm 1.25V 2 3 1616BD GND FB
U OPERATIO (Refer to Block Diagram)
The LT1616 is a constant frequency, current mode Buck SHDN pin is used to place the LT1616 in shutdown, regulator. The 1.4MHz oscillator enables an RS flip-flop, disconnecting the output and reducing the input current turning on the internal 600mA power switch Q1. An ampli- to less than 1µA. fier and comparator monitor the current flowing between The switch driver operates from either the input or from the VIN and SW pins, turning the switch off when this current the BOOST pin. An external capacitor and diode are used reaches a level determined by the voltage at VC. An error to generate a voltage at the BOOST pin that is higher than amplifier measures the output voltage through an external the input supply. This allows the driver to fully saturate the resistor divider tied to the FB pin. This amplifier servos the internal bipolar NPN power switch for efficient operation. switch current to regulate the FB pin voltage to 1.25V. An active clamp on the V The oscillator reduces the LT1616’s operating frequency C node provides current limit. when the voltage at the FB pin is low. This frequency An internal regulator provides power to the control cir- foldback helps to control the output current during start- cuitry. This regulator includes an undervoltage lockout to up and overload. prevent switching when VIN is less than ~ 3.5V. The 5