A Simple, Compact Power Solution for Optical Modules


Yi Sun, Power Module Products Manager at Monolithic Power Systems Inc.
Jinqian Yu at Monolithic Power Systems Inc.

High efficiency, excellent thermal performances, small footprint, and low emissions become challenges for power solutions in high-speed, high-density optical modules. This article introduces the MPM38222, a high-performance, 6V input, dual 2A power module, which is suitable for optical modules and other space-limited applications. The total solution for a dual 2A resides in a 9mmx7mm area with 90% efficiency and can meet EN55022 Class B emissions. The Module is available in a small QFN-14 (4mmx4mmx1.6mm) package.

 

Introduction

High-speed, high-density optical modules are widely adopted as interfaces that connect fibers to copper networks, data centers, and most endpoints in optical networks. As more components are integrated into the modules, higher efficiency, better thermal performances, smaller footprint, and low emissions become challenges for power solutions. MPS has created an easy and high-performance solution for optical modules and other space-limited power supplies. The proprietary packaging technology of MPS’s power modules has given them an edge over other competitors. For space-limited power designs, the smallest solution size possible is often desirable with no performance compromise. With this in mind, MPS is proud to present their MPM38222 dual 2A module to the industry.

 

Small Package with Dual Outputs

Space matters in optical modules and similar products. The MPM38222 is a dual-channel DC/DC module in a compact 4x4x1.6mm package. It has two output channels, and each channel can supply up to 2A of current. Just two or three devices can cover most power rails in an optical module.

 

Assembly Process

Figure 1: Assembly Process

 

Two chip inductors and the entire power stage are integrated inside the module (see Figure 1). As a result, compared to a discrete design solution, the Module only needs a minimal number of external components and functions as a full power system. Figure 2 shows the typical application circuit and layout for a 2.7V to 6V input, 1.2V/2A, and 1.8V/2A output applications. Only a few external ceramic capacitors and feedback resistors are required for each channel. The total solution size is only 9x7=63mm2 of PCB area. It provides a simple power system that’s easy to use, especially in space-limited applications.

 

Typical Application and Layout

Figure 2: Typical Application and Layout

 

The MPM38222 operates from a 2.7V to 6V input, generates an output voltage as low as 0.608V, and has a 45μA quiescent current, making it ideal for powering portable equipment that runs on battery cells.

 

High Efficiency at Light Load

Optical modules usually operate at loads of hundreds of mA. The device can achieve at least 90% efficiency between 10mA to 1A (see Figure 3).

 

Efficiency vs. Load Current

Figure 3: Efficiency vs. Load Current

 

In this load range, the MPM38222 uses a proprietary control scheme to save power and improve efficiency. The low-side switch is turned off when the inductor current starts to reverse and works in discontinuous conduction mode (DCM) operation. This helps skip pulses and reduce the switching frequency, minimizing switching loss.

 

Low-Noise Design

In addition to being small in size, the MPM38222 also has minimal EMI noise to its surroundings. Thanks to its high switching frequency, it can provide a clean output with peak-to-peak voltage ripple less than 20mV using only one 22µF 0603 ceramic capacitor. For the input side, the device employs a 180° phase shift between the two channels, which minimizes the input voltage ripple. It is also engineered to meet low EMI standards. Figure 4 shows its radiated EMI performance (EN55022 Class B).

 

 

Radiated EMI Test

Figure 4: Radiated EMI Test

 

Good Thermal Performances

Figure 5a shows the thermal image for 5V input, [email protected], and [email protected], while Figure 5b shows the same voltage @ 2A load current for both channels. For 1A load conduction, the temperature rise is only 22°C above the ambient 25°C without heatsink or forced airflow. For a 2A condition, the temperature rise is only 45°C. This excellent thermal performance enables the Module to work stably in a constraint space environment with high ambient temperature. Protection Features The MPM38222 includes various protection features to ensure a reliable and safe design.

  1. Soft start: A soft start with a controlled slew rate helps prevent input current overshoot during power-up.
  2. Over-current protection and hiccup: The Module limits the peak-current limit on a cycle-by-cycle basis. The device enters hiccup mode when the output is shorted to ground.
  3. Thermal shutdown: It shuts down the device when its junction temperature reaches 160°C.

 

Thermal Image: 5V Input, 1.8V@1A, 1.2A@1A

Figure 5a: Thermal Image: 5V Input, [email protected], [email protected]

Thermal Image: 5V Input, 1.8V@2A, 1.2A@2A

Figure 5b: Thermal Image: 5V Input, [email protected], [email protected]

 

For more detailed protection features, please refer to the datasheet.

 

Conclusion

The MPM38222’s high efficiency, low noise, and small size make it a great candidate for optical modules and other space-limited designs. The highly integrated module helps ease the design and shortens the time to market.

 

About the Authors

Yi Sun works as the Manager of Power Module Products in Monolithic Power Systems Inc. He has deep knowledge on design, modeling and control of power converters. He is responsible for technical product marketing, strategic business development, with power semiconductor companies in consumer electronics, telecom, computing, and automotive markets. He earned his Bachelor's and Master's degree in Electrical and Electronics Engineering at Tsinghua University, Beijing, China. He also acquired a Master's degree in Electrical Engineering at Virginia Tech, Blacksburg, Virginia, USA. 

Jinqian Yu is working at Monolithic Power System Inc. as an Application Engineer. He is primarily responsible for isolated and / Non-isolated DC/DC power module development. He earned his Bachelor's Degree in Electrical and Electronics Engineering at Changsha University of Science and Technology, Changsha, Hunan, China. He then acquired his Master's Degree in Electrical and Computer Engineering at  Texas A&M University, Texas, USA. 

 

More information: Monolithic Power Systems Inc.    Source: Bodo's Power Systems, October 2017