High Efficiency Buck + VLDO Regulator

The LTC3541-2 combines a synchronous buck DC/DC converter with a very low dropout linear regulator (VLDO™regulator) and internal feedback resistor networks to provide two output voltages from a single input voltage with minimal external components. When configured for dual output operation, the LTC3541-2’s auto start-up feature will bring the 1.875V buck output into regulation in a controlled manner, prior to enabling the 1.5V VLDO output without the need for external pin control. The 1.5V VLDO/linear regulator output prior to 1.875V buck output sequencing may also be obtained via external pin control. The input voltage range is ideally suited for Li-Ion battery applications powering sub-3.3V logic from 5V or 3.3V rails.

The synchronous buck converter provides a high efficiency output, typically 90%. It can provide up to 500mA of 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 output current using only a 2.2μF ceramic capacitor. The input supply voltage of the VLDO regulator (LVIN) may come from the buck regulator output 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

1.575 fixed

VLDO, then switcher

Applications

* 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 Buck Output Prior to VLDO/Linear Regulator Output

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

* 300mA VLDO Regulator with 30mA Standalone Mode

* No External Schottky Diodes Required

* Fixed Buck Output Voltage: 1.875V

* VLDO Input Voltage Range (LVIN: 1.6V to 5.5V)

* Fixed VLDO Output Voltage: 1.5V

* Selectable Fixed Frequency, Pulse-Skip Operation or Burst Mode® Operation

* Short-Circuit Protected

* Current Mode Operation for Excellent Line and Load Transient Response

* Shutdown Current: <3μA

* Constant Frequency Operation: 2.25MHz

* Low Dropout Buck Operation: 100% Duty Cycle

* Small, Thermally Enhanced, 10-Lead (3mm × 3mm) DFN Package