Features

• 1.6V to 5.5V Input Voltage Range
• Internal Soft-Start
• Low Ripple Burst Mode® Operation
    Output Ripple: <20mVP-P
    IQ: 50µA
• 2.25MHz Constant-Frequency Operation
• High Effi ciency: Up to 93%
• 250mA Output Current (VIN = 1.8V, VOUT = 1.2V)
• 450mA Peak Inductor Current
• No Schottky Diode Required
• Low Dropout Operation: 100% Duty Cycle
• 0.611V Reference Voltage
• Stable with Ceramic Capacitors
• Shutdown Mode Draws <1µA Supply Current
• Current Mode Operation for Excellent Line and Load Transient Response
• Overtemperature Protection
• Available in a Low Profi le (0.75mm) 6-Lead (2mm x 3mm) DFN Package

Typical Application

Description

The LTC3549 is a high efficiency, monolithic synchronous buck regulator using a constant-frequency, current mode architecture. The output voltage is adjusted via an external resistor divider.

 A fixed switching frequency of 2.25MHz is supported. This switching frequency allows the use of small surface mount inductors and capacitors, including ceramics.

 Supply current during Burst Mode operation is only 50µA dropping to < 1µA in shutdown. The 1.6V to 5.5V input voltage range makes the LTC3549 ideally suited for single cell Li-Ion, Li-Metal and 2-cell alkaline, NiCd or NiMH battery-powered applications. 100% duty cycle capability provides low dropout operation, extending battery life in portable systems. Burst Mode operation can be user-enabled, increasing efficiency at light loads, further extending battery life.

 The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. Internal soft-start offers controlled output voltage rise time at startup without the need for external components.