Datasheet LT3493 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | 1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN |
| Pages / Page | 20 / 7 — OPERATION (Refer to Block Diagram) |
| File Format / Size | PDF / 607 Kb |
| Document Language | English |
OPERATION (Refer to Block Diagram)
Model Line for this Datasheet
Text Version of Document
LT3493
OPERATION (Refer to Block Diagram)
The LT3493 is a constant frequency, current mode step- An internal regulator provides power to the control circuitry. down regulator. A 750kHz oscillator enables an RS fl ip-fl op, This regulator includes an undervoltage lockout to prevent turning on the internal 1.75A power switch Q1. An amplifi er switching when VIN is less than ~3.4V. The SHDN pin is and comparator monitor the current fl owing between the used to place the LT3493 in shutdown, disconnecting the VIN and SW pins, turning the switch off when this current output and reducing the input current to less than 2μA. reaches a level determined by the voltage at VC. An error The switch driver operates from either the input or from amplifi er measures the output voltage through an external the BOOST pin. An external capacitor and diode are used resistor divider tied to the FB pin and servos the VC node. to generate a voltage at the BOOST pin that is higher than If the error amplifi er’s output increases, more current is the input supply. This allows the driver to fully saturate the delivered to the output; if it decreases, less current is internal bipolar NPN power switch for effi cient operation. delivered. An active clamp (not shown) on the VC node provides current limit. The V The oscillator reduces the LT3493’s operating frequency C node is also clamped to the voltage on the SHDN pin; soft-start is implemented when the voltage at the FB pin is low. This frequency by generating a voltage ramp at the SHDN pin using an foldback helps to control the output current during start- external resistor and capacitor. up and overload. 3493fb 7
OPERATION (Refer to Block Diagram)
The LT3493 is a constant frequency, current mode step- An internal regulator provides power to the control circuitry. down regulator. A 750kHz oscillator enables an RS fl ip-fl op, This regulator includes an undervoltage lockout to prevent turning on the internal 1.75A power switch Q1. An amplifi er switching when VIN is less than ~3.4V. The SHDN pin is and comparator monitor the current fl owing between the used to place the LT3493 in shutdown, disconnecting the VIN and SW pins, turning the switch off when this current output and reducing the input current to less than 2μA. reaches a level determined by the voltage at VC. An error The switch driver operates from either the input or from amplifi er measures the output voltage through an external the BOOST pin. An external capacitor and diode are used resistor divider tied to the FB pin and servos the VC node. to generate a voltage at the BOOST pin that is higher than If the error amplifi er’s output increases, more current is the input supply. This allows the driver to fully saturate the delivered to the output; if it decreases, less current is internal bipolar NPN power switch for effi cient operation. delivered. An active clamp (not shown) on the VC node provides current limit. The V The oscillator reduces the LT3493’s operating frequency C node is also clamped to the voltage on the SHDN pin; soft-start is implemented when the voltage at the FB pin is low. This frequency by generating a voltage ramp at the SHDN pin using an foldback helps to control the output current during start- external resistor and capacitor. up and overload. 3493fb 7
