Analog Devices Inc. LTC3407EMSE#TRPBF

LTC3407EMSE#TRPBF Dual DC/DC Converter Product Summary

The LTC3407EMSE#TRPBF from Analog Devices is a dual, high-efficiency, synchronous step-down DC/DC converter, ideally designed for demanding low-power portable applications. Housed in a compact 10-lead MSOP or DFN package with exposed thermal pad, each channel supports up to 600mA output current, with output voltages adjustable from 0.6V to 5V. The device operates from a 2.5V to 5.5V input voltage range, covering typical single-cell lithium-ion battery voltages and logic rails. With integrated low on-resistance power switches and a constant 1.5MHz switching frequency, the LTC3407EMSE#TRPBF enables the use of small external components, making it suitable for space-constrained designs.

Main Characteristics of the LTC3407EMSE#TRPBF

Efficiency is a central feature of the LTC3407EMSE#TRPBF, with peak efficiencies up to 96% under optimal load conditions. The device offers extremely low quiescent current of just 40μA for both channels combined, and in shutdown, current consumption drops further to under 1μA. Each channel's output can be individually enabled, and the device's operation is protected by short-circuit and under-voltage lockout circuitry.

Switches with 0.35Ω on-resistance ensure minimal conduction losses, while current mode control provides consistent line and load transient response. The device also supports mode selection between Burst Mode® operation for high efficiency at light loads and pulse-skipping mode for low output ripple, as well as the ability to synchronize to an external clock. No external Schottky diodes are required, further reducing component count.

Ideal Use Cases for the LTC3407EMSE#TRPBF

The LTC3407EMSE#TRPBF is targeted at portable and battery-powered equipment where high efficiency and compact design are paramount. Key application areas include:

PDAs and palmtop PCs

Digital cameras

Cellular phones and portable media players

PC cards

Wireless and DSL modems

The dual, independently enabled regulators are particularly valuable where multiple supply rails are needed from a shared input, such as in multimedia devices or communication modules.

LTC3407EMSE#TRPBF Internal Functionality and Control System

The LTC3407EMSE#TRPBF employs a constant-frequency, current mode architecture. Both output channels operate in phase, sharing the same internal clock. Output voltages are set using an external resistor divider network, with a reference voltage of 0.6V, and feedback is actively regulated via internal error amplifiers.

At each switching cycle, the control loop adjusts the inductor peak current, responding quickly to changes in load or input voltage, which ensures robust transient performance. In dropout conditions (input voltage approaches output voltage), the high-side switch remains on continuously, providing near 100% duty cycle operation. Under-voltage lockout is implemented to avoid operation when supply voltages are insufficient for regulation.

LTC3407EMSE#TRPBF Pinout and Function Descriptions

The LTC3407EMSE#TRPBF is available in thermally enhanced 10-lead MSOP and DFN packages. Key pins include:

VIN: Main supply input (2.5V–5.5V) with close-coupled decoupling required.

SW1 and SW2: Switch nodes for each regulator, connect to their corresponding inductors.

VFB1/VFB2: Feedback inputs for output voltage setting; nominal at 0.6V.

RUN1/RUN2: Enable inputs for the respective channels.

MODE/SYNC: Selects between operating modes and enables frequency synchronization.

POR: Open-drain power-on reset output for system monitoring.

GND and Exposed Pad: Ground connections; for optimal thermal and electrical performance, the exposed pad must be soldered to PCB ground.

LTC3407EMSE#TRPBF Design Guide Inductor, Capacitor, and Voltage Setting Recommendations

Inductor selection directly influences ripple current and output voltage noise. Typical applications employ inductors in the 2.2μH range, but values should be optimized based on desired ripple and maximum input voltage as per the datasheet's equations. Ferrite or shielded-core inductors are recommended for low EMI.

Input capacitor (CIN) selection is critical for suppressing voltage transients. A low ESR ceramic capacitor of 10μF is generally sufficient, but must be rated for the maximum expected RMS current. The output capacitor (COUT) selection is driven primarily by ESR requirements for voltage ripple and transient response. Ceramic, tantalum, and special polymer capacitors are commonly used; the selection depends on required size, cost, and ESR, with ceramic types recommended for their low ESR and high reliability.

Output voltage setting is achieved via a resistor divider from the output to the VFB pin, using the formula VOUT = 0.6V × (1 + R2/R1). To maintain efficiency and avoid instability, divider currents should be kept below 5µA.

Operating States and Frequency Coordination in the LTC3407EMSE#TRPBF

The MODE/SYNC pin allows for selection of operating mode:

Burst Mode® operation minimizes losses at light loads, benefiting battery runtime but with higher output voltage ripple.

Pulse-skipping mode reduces output voltage ripple at the expense of some efficiency under light loads.

Externally applied clock to the MODE/SYNC pin enables synchronization, which may be crucial in systems requiring fixed frequency operation to avoid interference with sensitive circuits.

System Reset and Monitoring Capabilities with the LTC3407EMSE#TRPBF

The POR (Power-On Reset) feature is a supervisory function: the POR pin pulls low if either output voltage drifts beyond ±8.5% of its regulation point. Once both channels recover regulation, POR is released after a programmable delay (typically 175ms). This function is useful for sequencing and safely powering downstream sensitive loads, especially in embedded or communication systems.

LTC3407EMSE#TRPBF Efficiency and Heat Dissipation Guidelines

Switch-mode DC/DC regulators inherently boost efficiency, but understanding the sources of loss is important for design optimization in the LTC3407EMSE#TRPBF:

Quiescent current: Maintained at just 40μA for both channels.

Switching losses: Dependent on gate charge associated with the switching MOSFETs and the switching frequency.

I²R losses: Determined by the on-resistance of internal switches and external inductor resistance.

Additional system losses: Include PCB trace resistance and external circuit elements.

Thermal management is typically straightforward due to the device's high efficiency, but calculations should be performed in high ambient conditions or high duty cycle applications. The junction temperature rise can be estimated using the package's thermal resistance and worst-case dissipation scenarios.

PCB Design Recommendations for the LTC3407EMSE#TRPBF

Proper PCB layout is essential for noise performance and thermal management:

Place input and output capacitors as close as possible to the LTC3407EMSE#TRPBF pins and the exposed pad ground.

Ensure a low-impedance ground connection by using ground planes and minimizing the path for high current.

Keep feedback and sensitive components away from the noisy SW nodes.

Route the feedback network for each channel directly to the output capacitor's ground node for optimal regulation accuracy.

Flood unused PCB areas with copper connected to ground to help dissipate heat.

LTC3407EMSE#TRPBF Standard Application Circuit Example

A common scenario involves converting a single-cell Li-Ion battery voltage (2.8V–4.2V) to lower logic voltages such as 2.5V and 1.8V for core and I/O rails. Utilizing the LTC3407EMSE#TRPBF, both outputs are programmed with efficient control—using a 2.2μH inductor and 10μF ceramic capacitors, as per datasheet recommendations. Burst Mode operation can be selected for efficient standby operation, ideal for systems where load can drop to the µA range between active cycles.

Comparable and Substitute Options for the LTC3407EMSE#TRPBF

While the LTC3407EMSE#TRPBF offers a specific blend of features (dual outputs, 600mA current capability, 1.5MHz operation, and low quiescent current), designers might also consider other Analog Devices DC/DC converters for applications requiring different combinations of channel count, output current, or switching frequency.

Potential alternatives can include:

LTC3407A series, which may offer adjusted frequency or current ratings.

LTC3548, which provides a similar dual output in a space-saving package.

LT1616/LT1618, for single-channel step-down needs at comparable current levels.

For markets demanding 1A or higher, LTC3411 or LTC3440 (step-down/step-up converters).

Device selection for replacement should be guided by considerations such as package compatibility, maximum input/output voltage, current rating, quiescent current, and the presence of advanced features such as frequency synchronization and system-level power monitoring.

Conclusion

The LTC3407EMSE#TRPBF by Analog Devices presents an optimal choice for engineers designing multi-rail, high-efficiency, and space-conscious power management solutions in modern portable and battery-powered systems. Its robust internal architecture, versatile application adaptability, and rich feature set simplify the delivery of multiple tightly-regulated supply rails with minimal external components. A thoughtfully executed PCB layout and attention to component selection, as discussed, will maximize performance and reliability in real-world engineering scenarios. When selecting DC/DC converter solutions, the LTC3407EMSE#TRPBF stands out as a highly integrated, dependable, and efficient core for advanced low-voltage designs.