Technical Article

Tiny µModule Boost Regulator for Low Voltage Optical Systems

May 16, 2018 by Roland R. Ackerman

Analog Devices, Inc. announced the "Power by Linear" LTM4661, a low power step-up µModule regulator in a 6.25mm x 6.25mm x 2.42mm BGA package.

Analog Devices, Inc. announced the "Power by Linear" LTM4661, a low power step-up µModule regulator in a 6.25mm x 6.25mm x 2.42mm BGA package. Only a few capacitors and one resistor are required to complete the design, and the solution occupies less than 1cm² single-sided or 0.5cm² on double-sided PCBs. The LTM4661 incorporates a switching DC/DC controller, MOSFETs, inductors and supporting components.

The main voltage rails in electrical equipment are going down to 2.5V, 1.8V, or even lower than 1.0V, but it is still common to find higher voltages including 5V for the interface, 12V for analog circuits and 5V or above for motor drive or bias power supply for optical devices such as laser and photodiode. Not only battery-operated equipment but also daughter boards and extension boards in industrial equipment often have limited voltage sources, which require a step-up converter to generate these voltages. The LTM4661 is Analog Devices’ first step-up regulator module which allows smaller solution size and simpler design.


The device allows smaller solution size and simpler design.
Figure 1: The device allows smaller solution size and simpler design.


The LTM4661 operates from a 1.8V to 5.5V input supply and continues to operate down to 0.7V after start-up. The output voltage can be set by a single resistor ranging from 2.5V to 15V. The combination of the small, thin package and wide input and output voltage range is ideal for wide range of applications including optical modules, battery-powered equipment, battery-based backup systems, bias voltage for power amps or laser diodes, and small DC motors.

The LTM4661 can deliver 4A continuously under 3.3VIN to 5VOUT, and 0.7A continuously under 3.3VIN to 12VOUT. The LTM4661 employs synchronous rectification, which delivers as high as 92% conversion efficiency (3.3VIN to 5VOUT). The switching frequency is 1MHz, and can also be synchronized to an external clock ranging from 500kHz to 1.5MHz. The LTM4661 1MHz switching frequency and dual phase single output architecture enable fast transient response to line and load changes and a significant reduction of output ripple voltage.

The LTM4661 has three operation modes: burst mode, forced continuous mode, and external sync mode. The quiescent current in burst mode operation is only 25µA, which provides extended battery runtime. For applications demanding the lowest possible noise operation, the forced continuous mode or external sync mode minimize possible interference of switching noise.


Figure 2: LTM4661 low power step-up µModule regulator


The LTM4661 features an output disconnect during shutdown and inrush current limit at start-up. Fault protection features include short-circuit, overvoltage and overtemperature protection. The LTM4661 operates from -40℃ to 125℃ operating temperature.


Table 1: Comparison between LTM4661 (Module) and LTC3124 (Discrete). The LTM4661 requires fewer external components.


Absolute Maximum Ratings

  • VIN: 0.3V to 6V
  • VOUT: 0.3V to 18V
  • COMP, FREQ: 0.3V to INTVCC
  • SYNC/MODE, SDB: 0.3V to 6V
  • Operating Internal Temperature Range: 40°C to 125°C
  • Storage Temperature Range: 55°C to 125°C
  • Peak Solder Reflow Body Temperature: 250°C



The LTM4661 is the Analog Devices’ first step-up regulator module. It requires only four external components, whereas an equivalent discrete solution requires about 15 components.


Summary of Features

  • Complete Solution in <1cm² (Single-Sided PCB) or 0.5cm² (Dual-Sided PCB)
  • Input Voltage Range: 1.8V to 5.5V, Down to 0.7V After Start-Up
  • Output Voltage Range: 2.5V to 15V
  • Up to 4A DC Output Current
  • ±2% Maximum Total DC Output Voltage Regulation Over Load, Line & Temperature
  • Output Disconnect in Shutdown
  • Inrush Current Limit
  • External Frequency Synchronization
  • Selectable Burst Mode® Operation
  • Output Overvoltage & Overtemperature Protection
  • Ultrathin 6.25mm × 6.25mm × 2.42mm BGA package


This. article originally appeared in the Bodo’s Power Systems magazine.