Datasheet LTM8025 (Analog Devices) - 9

LTM8025
BLOCK DIAGRAM
VIN 8.2µH VOUT 499k 0.2µF 15pF 4.4µF AUX BIAS RUN/SS CURRENT MODE SHARE CONTROLLER SYNC GND RT PGOOD ADJ 8025 BD
OPERATION
The LTM8025 is a standalone nonisolated step-down To further optimize efficiency, the LTM8025 automatical y switching DC/DC power supply that can deliver up to switches to Burst Mode® operation in light load situations. 3A of output current. This module provides a precisely Between bursts, all circuitry associated with controlling regulated output voltage programmable via one external the output switch is shut down reducing the input supply resistor from 0.8V to 25V. The input voltage range is 3.6V current to 50μA in a typical application. to 36V. Given that the LTM8025 is a step-down converter, The oscillator reduces the LTM8025’s operating frequency make sure that the input voltage is high enough to support when the voltage at the ADJ pin is low. This frequency the desired output voltage and load current. foldback helps to control the output current during start- As shown in the Block Diagram, the LTM8025 contains a up and overload. current mode control er, power switching element, power The LTM8025 contains a power good comparator which inductor, power Schottky diode and a modest amount of trips when the ADJ pin is at roughly 90% of its regulated input and output capacitance. The LTM8025 is a fixed value. The PGOOD output is an open-collector transistor frequency PWM regulator. The switching frequency is set that is off when the output is in regulation, allowing an by simply connecting the appropriate resistor value from external resistor to pull the PGOOD pin high. Power good is the RT pin to GND. valid when the LTM8025 is enabled and VIN is above 3.6V. An internal regulator provides power to the control cir- The LTM8025 is equipped with a thermal shutdown that cuitry. The bias regulator normally draws power from the will inhibit power switching at high junction tempera- VIN pin, but if the BIAS pin is connected to an external volt- tures. The activation threshold of this function, however, age higher than 2.8V, bias power will be drawn from the is above 125°C to avoid interfering with normal operation. external source (typically the regulated output voltage). Thus, prolonged or repetitive operation under a condition This improves efficiency. The RUN/SS pin is used to place in which the thermal shutdown activates may damage or the LTM8025 in shutdown, disconnecting the output and impair the reliability of the device. reducing the input current to less than 1μA. Rev. D For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Package Photography Typical Application Related Parts