Datasheet LTM8029 (Analog Devices) - 10

LTM8029
OPERATION
The LTM8029 is a standalone non-isolated step-down typically 5μA at no load and 12VIN. Since the LTM8029 is switching DC/DC power supply that can deliver up to 600mA mostly shut down between bursts, the effective switching of output current. This device features a very low quiescent frequency will be lower than that programmed at the RT current and provides a precisely regulated output voltage pin. For the same reason, the output ripple will be differ- from 1.2V to 18V. The input voltage range is 4.5V to 36V. ent than when the part is running at the full programmed Given that the LTM8029 is a step-down converter, make frequency. sure that the input voltage is high enough to support the The LTM8029 contains a power good comparator which desired output voltage and load current. trips when the FB pin is at roughly 90% of its regulated As shown in the Block Diagram, the LTM8029 contains a value. The PGOOD output is an open-collector transistor current mode controller, power switching element, power that is off when the output is in regulation, allowing an inductor, power Schottky diode and a modest amount of external resistor to pull the PGOOD pin high. Power good input and output capacitance. The LTM8029 is a fixed is valid when the LTM8029 is enabled and VIN is above frequency PWM regulator. The switching frequency is set 4.5V. The LTM8029 features the ability to skip the off-time by simply connecting the appropriate resistor value from in switching cycles when the input voltage approaches the the RT pin to GND. An internal regulator provides power target output. This allows the LTM8029 to operate at input to the control circuitry. voltages lower than other step-down regulators. The internal regulator normally draws power from the VIN In an overload or short-circuit condition, the LTM8029 pin, but if the BIAS pin is connected to an external volt- will protect itself by limiting its peak switching current age higher than 2.25V, bias power will be drawn from the and decreasing the operating frequency to reduce overall external source (typically the regulated output voltage). power consumption. The LTM8029 is also equipped with This improves efficiency. a thermal shutdown that will inhibit power switching at The RUN pin is used to place the LTM8029 in shutdown. high junction temperatures. The activation threshold of this To optimize efficiency, the LTM8029 automatically switches function, however, is above 125°C to avoid interfering with to Burst Mode operation in light load situations. Between normal operation. Thus, prolonged or repetitive operation bursts, all circuitry associated with controlling the output under a condition in which the thermal shutdown activates switch is shut down reducing the input supply current to may damage or impair the reliability of the device. Rev. E 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Application Package Description Revision History Package Photo Design Resources Related Parts