LTC3406B

Part: LTC3406 from Linear Technology Corporation

Type: Synchronous Buck Regulator

Description: 2.5–5.5 V input, 600 mA synchronous buck regulator with 1.5 MHz constant frequency operation and up to 96% peak efficiency.

Operating Conditions:

• Supply voltage: 2.5–5.5 V
• Operating temperature: –40 to 85 °C
• Max output current: 600 mA
• Switching frequency: 1.5 MHz

Absolute Maximum Ratings:

• Max junction temperature: 125 °C
• Max storage temperature: –65 to 150 °C

Key Specs:

• Input voltage range: 2.5 V to 5.5 V
• Regulated feedback voltage: 0.5850 V to 0.6150 V (over –40°C to 85°C)
• Oscillator frequency: 1.2 MHz to 1.8 MHz (over full operating temp range)
• Active mode quiescent current: 20 μA (typ)
• Peak inductor current: 0.75 A (min)
• P-channel FET R_DS(ON): 0.4 Ω (typ) at I_SW = 100 mA
• N-channel FET R_DS(ON): 0.35 Ω (typ) at I_SW = –100 mA
• Peak efficiency: Up to 96%

Features:

• High Efficiency: Up to 96%
• Very Low Quiescent Current: Only 20μA During Operation
• 600mA Output Current
• 2.5V to 5.5V Input Voltage Range
• 1.5MHz Constant Frequency Operation
• No Schottky Diode Required
• Low Dropout Operation: 100% Duty Cycle
• 0.6V Reference Allows Low Output Voltages
• Shutdown Mode Draws ≤ 1μA Supply Current
• Current Mode Operation for Excellent Line and Load Transient Response
• Overtemperature Protected
• Low Profile (1mm) ThinSOT™ Package

Applications:

• Cellular Telephones
• Personal Information Appliances
• Wireless and DSL Modems
• Digital Still Cameras
• MP3 Players
• Portable Instruments

Package:

• ThinSOT (1mm profile)

• High Efficiency: Up to 96%
• Very Low Quiescent Current: Only 20μA During Operation
• 600mA Output Current
• 2.5V to 5.5V Input Voltage Range
• 1.5MHz Constant Frequency Operation
• No Schottky Diode Required
• Low Dropout Operation: 100% Duty Cycle
• 0.6V Reference Allows Low Output Voltages
• Shutdown Mode Draws ≤ 1μA Supply Current
• Current Mode Operation for Excellent Line and Load Transient Response
• Overtemperature Protected
• Low Profile (1mm) ThinSOT^™ Package

• Cellular Telephones
• Personal Information Appliances
• Wireless and DSL Modems
• Digital Still Cameras
• MP3 Players
• Portable Instruments

DESCRIPTION

The LTC®3406 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. The device is available in an adjustable version and fixed output voltages of 1.5V and 1.8V. Supply current during operation is only 20μ A and drops to ≤ 1μ A in shutdown. The 2.5V to 5.5V input voltage range makes the LTC3406 ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. Automatic Burst Mode® operation increases efficiency at light loads, further extending battery life.

Switching frequency is internally set at 1.5MHz, allowing the use of small surface mount inductors and capacitors.

The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. Low output voltages are easily supported with the 0.6V feedback reference voltage. The LTC3406 is available in a low profile (1mm) ThinSOT package.

47, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. Protected by U.S. Patents, including 6580258, 5481178.

RUN (Pin 1): Run Control Input. Forcing this pin above 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. In shutdown, all functions are disabled drawing <1μ A supply current. Do not leave RUN floating.

V_1N = 3.6V

V_0UT = 1.8V

I_LOAD = 100mA TO 600mA

20μs/DIV

GND (Pin 2): Ground Pin.

SW (Pin 3): Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches.

V_IN (Pin 4): Main Supply Pin. Must be closely decoupled to GND, Pin 2, with a 2.2μ F or greater ceramic capacitor.

20μs/DIV

3406 G20

V_IN = 3.6V

V_OUT = 1.8V

I_LOAD = 200mA TO 600mA

V_FB (Pin 5) (LTC3406): Feedback Pin. Receives the feedback voltage from an external resistive divider across the output.

V_OUT (Pin 5) (LTC3406-1.5/LTC3406-1.8): Output Voltage Feedback Pin. An internal resistive divider divides the output voltage down for comparison to the internal reference voltage.

FUNCTIONAL DIAGRAM

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 3.6V unless otherwise specified.

In most applications the LTC3406 does not dissipate much heat due to its high efficiency. But, in applications where the LTC3406 is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 150°C, both power switches will be turned off and the SW node will become high impedance.

To avoid the LTC3406 from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The temperature rise is given by:

$T_R = (P_D)(θ_JA)$

where $P_D$ is the power dissipated by the regulator and $\theta_{JA}$ is the thermal resistance from the junction of the die to the ambient temperature.

LINEAR

Figure 1a. High Efficiency Step-Down Converter

Figure 1b. Efficiency vs Load Current

ABSOLUTE AXI U RATI GS W W W U (Note 1)

Peak SW Sink and Source Current ........................ 1.3A Operating Temperature Range (Note 2) .. –40°C to 85°C Junction Temperature (Note 3)............................ 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C