High Efficiency Buck + VLDO Regulator

The LTC3541-1 combines a synchronous buck DC/DC converter with a very low dropout linear regulator (VLDO) to provide up to two output voltages from a single input voltage with minimal external components. When configured for dual output operation, the LTC3541-1’s auto start-up feature will bring the VLDO/linear regulator output into regulation in a controlled manner prior to enabling the Buck regulator output without the need for external pin control. Buck output prior to VLDO/linear regulator output sequencing may also be obtained via external pin control. The input voltage range is ideally suited for Li-Ion battery-powered applications, as well as powering sub-3.3V logic from 5V or 3.3V rails.

The synchronous buck converter provides a high efficiency output, typically 90%, capable of providing up to 500mA of continuous output current while switching at 2.25MHz, allowing the use of small surface mount inductors and capacitors. A mode-select pin allows Burst Mode operation to be enabled for higher efficiency at light load currents, or disabled for lower noise, constant frequency operation.

The VLDO regulator provides a low noise, low voltage output capable of providing up to 300mA of continuous output current using only a 2.2µF ceramic capacitor. The input supply voltage of the VLDO regulator (LVIN) may come from the buck regulator or a separate supply.

Options

VOUT Switcher (V)

VOUT VLDO

Auto Start-Up Sequencing

LTC3541

Adj. down to 0.8V

Adj. down to 0.4V

Switcher, then VLDO

LTC3541-1

Adj. down to 0.8V

Adj. down to 0.4V

VLDO, then switcher

LTC3541-2

1.875V fixed

1.5V fixed

Switcher, then VLDO

LTC3541-3

1.8V fixed

1.575V fixed

VLDO, then switcher

Applications

* PDAs/Palmtop PCs

* Digital Cameras

* Cellular Phones

* PC Cards

* Wireless and DSL Modems

* Other Portable Power Systems

* High Efficiency, 500mA Buck Plus 300mA VLDO™ Regulator

* Auto Start-Up Powers VLDO/Linear Regulator Output Prior to Buck Regulator Output

* Independent High Efficiency, 500mA Buck (VIN: 2.7V to 5.5V)

* 300mA VLDO Regulator with 30mA Standalone Mode

* No External Schottky Diodes Required

* Buck Output Voltage Range: 0.8V to 5V

* VLDO Input Voltage Range (LVIN): 0.9V to 5.5V