Datasheet LTM8022 (Analog Devices) - 7

LTM8022
BLOCK DIAGRAM
VIN V 4.7μH OUT AUX 0.1μF 4.7pF 499k 10μF BIAS SHARE CURRENT MODE CONTROLLER RUN/SS PG SYNC GND RT ADJ 8022 BD
OPERATION
The LTM8022 is a standalone non-isolated step-down voltage higher than 2.4V, bias power will be drawn from switching DC/DC power supply. It can deliver up to 1A of the external source (typically the regulated output voltage). DC output current with only bulk external input and output This improves effi ciency. The RUN/SS pin is used to place capacitors. This module provides a precisely regulated the LTM8022 in shutdown, disconnecting the output and output voltage programmable via one external resistor reducing the input current to less than 1μA. from 0.8VDC to 10VDC. The input voltage range is 3.6V to To further optimize effi ciency, the LTM8022 automatically 36V. Given that the LTM8022 is a step-down converter, switches to Burst Mode operation in light load situations. make sure that the input voltage is high enough to support Between bursts, all circuitry associated with controlling the the desired output voltage and load current. A simplifi ed Block Diagram is shown above. output switch is shut down reducing the input supply cur- rent to 50μA in a typical application. The oscillator reduces The LTM8022 contains a current mode controller, power the LTM8022’s operating frequency when the voltage at the switching element, power inductor, power Schottky diode ADJ pin is low. This frequency foldback helps to control and a modest amount of input and output capacitance. the output current during start-up and overload. The LTM8022 is a fi xed frequency PWM regulator. The The LTM8022 contains a power good comparator which switching frequency is set by simply connecting the trips when the ADJ pin is at 92% of its regulated value. appropriate value resistor from the RT pin to GND. The PG output is an open-collector transistor that is off An internal regulator provides power to the control cir- when the output is in regulation, allowing an external cuitry. The bias regulator normally draws power from the resistor to pull the PG pin high. Power good is valid when VIN pin, but if the BIAS pin is connected to an external the LTM8022 is enabled and VIN is above 3.6V. 8022fd 7