LTC3541-3

High Efficiency 500mA Buck Plus 300mA VLDORegulator Auto Start-Up Powers VLDO/Linear Regulator Output Prior to Buck Output
Independent 500mA High Efficiency Buck (V_IN: 2.7V to 5.5V)
300mA VLDO Regulator with 30mA Standalone Mode
No External Schottky Diodes Required
Fixed Buck Output Voltage: 1.8V
VLDO Input Voltage Range (LV_IN: 1.675V to 5.5V)
Fixed VLDO Output Voltage: 1.575V
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: <3A
Constant Frequency Operation: 2.25MHz
Low Dropout Buck Operation: 100% Duty Cycle
Small, Thermally Enhanced, 10-Lead (3mm * 3mm) DFN Package

The LTC^®3541-3 combines a synchronous buck DC/ DC converter with a very low dropout linear regulator (VLDOTM regulator) and internal feedback resistor networks to provide two output voltages from a single input voltage with minimum external components. When configured for dual output operation, the LTC3541-3's auto start-up feature will bring the 1.575V VLDO/linear regulator output into regulation in a controlled manner prior to enabling the 1.8V buck output without the need for external pin control. The 300mA VLDO/linear regulator output will source only 30mA until the buck output achieves regulation. The input voltage range is ideally suited for applications powered from a Li-Ion battery and 5V or 3.3V rails.

The synchronous buck converter of LTC3541-3 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 of LTC3541-3 provides a low noise, low voltage output capable of providing up to 300mA of output current using only a 2.2F ceramic capacitor. The input supply voltage of the VLDO regulator (LV_IN) may come from the buck regulator or a separate supply.