Datasheet LT1912 (Analog Devices) - 8
| Manufacturer | Analog Devices |
| Description | 36V, 2A, 500kHz Step-Down Switching Regulator |
| Pages / Page | 24 / 8 — OPERATION |
| File Format / Size | PDF / 379 Kb |
| Document Language | English |
OPERATION
Model Line for this Datasheet
Text Version of Document
LT1912
OPERATION
The LT1912 is a constant frequency, current mode step- but if the BD pin is connected to an external voltage higher down regulator. An oscillator, with frequency set by RT, than 3V bias power will be drawn from the external source enables an RS flip-flop, turning on the internal power (typically the regulated output voltage). This improves switch. An amplifier and comparator monitor the current efficiency. The RUN/SS pin is used to place the LT1912 flowing between the VIN and SW pins, turning the switch in shutdown, disconnecting the output and reducing the off when this current reaches a level determined by the input current to less than 1µA. voltage at VC. An error amplifier measures the output The switch driver operates from either the input or from voltage through an external resistor divider tied to the FB the BOOST pin. An external capacitor and diode are used pin and servos the VC pin. If the error amplifier’s output to generate a voltage at the BOOST pin that is higher than increases, more current is delivered to the output; if it the input supply. This allows the driver to fully saturate the decreases, less current is delivered. An active clamp on the internal bipolar NPN power switch for efficient operation. VC pin provides current limit. The VC pin is also clamped to the voltage on the RUN/SS pin; soft-start is implemented The oscillator reduces the LT1912’s operating frequency by generating a voltage ramp at the RUN/SS pin using an when the voltage at the FB pin is low. This frequency external resistor and capacitor. foldback helps to control the output current during start- up and overload. An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the VIN pin, 1912fa 8 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
OPERATION
The LT1912 is a constant frequency, current mode step- but if the BD pin is connected to an external voltage higher down regulator. An oscillator, with frequency set by RT, than 3V bias power will be drawn from the external source enables an RS flip-flop, turning on the internal power (typically the regulated output voltage). This improves switch. An amplifier and comparator monitor the current efficiency. The RUN/SS pin is used to place the LT1912 flowing between the VIN and SW pins, turning the switch in shutdown, disconnecting the output and reducing the off when this current reaches a level determined by the input current to less than 1µA. voltage at VC. An error amplifier measures the output The switch driver operates from either the input or from voltage through an external resistor divider tied to the FB the BOOST pin. An external capacitor and diode are used pin and servos the VC pin. If the error amplifier’s output to generate a voltage at the BOOST pin that is higher than increases, more current is delivered to the output; if it the input supply. This allows the driver to fully saturate the decreases, less current is delivered. An active clamp on the internal bipolar NPN power switch for efficient operation. VC pin provides current limit. The VC pin is also clamped to the voltage on the RUN/SS pin; soft-start is implemented The oscillator reduces the LT1912’s operating frequency by generating a voltage ramp at the RUN/SS pin using an when the voltage at the FB pin is low. This frequency external resistor and capacitor. foldback helps to control the output current during start- up and overload. An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the VIN pin, 1912fa 8 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
