MPS Power Management Solutions for Power over Ethernet (PoE) Switches

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Introduction

Modern devices are increasingly powered by Power over Ethernet (PoE), such as IP phones, wireless APs, and IP cameras. Customer premise equipment (CPE) and small base stations in the 5G era also require PoE power.

Figure 1 shows common applications powered by PoE.

Figure 1: Common Applications Powered by PoE

This article discusses MPS’s comprehensive suite of power management solutions for a wide range of switches, including PSE, boost, high-voltage buck/flyback, high-current buck, and 2A to 3A buck.

PoE Switch Power Structure and Adapter Types

PoE offers clear advantages, as it does not require additional adapters and power cables, and can transmit both data and power through network cables.

The switch is a common device that can provide a PoE power supply. Figure 2 shows the PoE switch’s power structure, which is typically powered by an AC to DC adapter.

Figure 2: Power Structure of the PoE Switch

There are three types of adapters, described below:

  1. 12V adapter power supply: With a 12V adapter, a voltage between 12V and 48V is required to supply the power-sourcing equipment (PSE) chip input.
  2. 48V/53V adapter power supply: With a 48V/53V adapter, 48V/53V can be directly supplied to the PSE, but a 48V/53V step-down IC is required to step down to 12V, 5V, 3.3V, and so on. For high-power switches, the voltage is typically stepped down to 12V first, then later stages often utilize high-current buck converters and 2A/3A buck converters.
  3. 48V/53V + 12V adapter power supply: For some high-power switches, the front-end adapter supplies two voltages. This means that the system can eliminate the 48V/53V boost or buck converter and directly use the 12V/5V buck converter to step down to Core, IO, or DDR.

MPS offers a wide range of power solutions for switches that can work with any front-end adapter. Table 1 shows the various MPS parts that can be selected depending on the application.

Table 1: MPS Power Solutions for Switches

Power-Sourcing Equipment (PSE)

The MP3924 is a quad-port PSE controller that is compatible with IEEE802.3af/at protocol. Its integrated VCC power supply addresses the challenges of the 48V to 3.3V power supply for the PSE chip. In addition, this device is available in a small QFN-32 (5mmx5mm) package that requires only one power MOSFET for single-port PSE applications, which reduces overall cost.

For configurability, the I2C interface can monitor the voltage and current of each port, as well as set the current limit of each port. A single port can support up to 40W of power. The MP3924’s PMAX pin sets the total power for all four ports. If the total power exceeds its limit, the ports with lower priority close automatically.

Figure 4 shows the typical application circuit of the MP3924, as well as its key features.

Figure 3: Typical Application Circuit and Key Features of the MP3924

Boost/Flyback

For 12V to 48V/53V applications, the MP3425 or MP3910 boost converter can be selected according to the power specifications. The MP3425 is a current mode step-up converter with a 3.5A, 90mΩ internal switch. Meanwhile, the MP3910 is a peak current mode pulse-width modulation (PWM) controller that can drive an external MOSFET capable of handling more than 10A of current.

In particular, the MP3910 supports isolation applications that can be boosted up to 48V/53V in a flyback topology.

High-Voltage Buck/Flyback

MPS also offers multiple solutions for non-isolated, 48V/53V step-down applications, according to the power requirements. These solutions include the MP9928, MP9572, MP9487, and MP4541 step-down converters.

For isolation applications, MPS also provides the MP6004 and MP6005 for different power levels.

MP9572

The MP9572 is a fully integrated, 60V/2A synchronous buck converter. Figure 4 shows the MP9572’s features, application circuit, and efficiency curve.

Figure 4: The MP9572 Details

The MP9572 is capable of a 12V/2A output with a high efficiency. Figure 5 shows the MP9572’s efficiency curve.

Figure 5: MP9572 Efficiency Curve

High-Current Buck Converters

For 5A to 30A applications, MPS provides a series of devices (e.g. isolators and buck converters) that can be selected according to Table 1.

2A to 3A Buck Converters

For 2A to 3A applications, the MP1657 and MP1658 are recommended due to their tiny SOT563 package, constant-on-time (COT) control, and excellent dynamic response.

Digital Isolators

The MP27631 is a quad-channel digital isolator that can support up to 150Mbps of data rate signal isolation.

For some isolation switches, the PSE registers (e.g. MP3924) must be configured via the I2C. Most of the switches isolate the I2C and reset the signals. Afterwards, the MP27631 can be used. Figure 6 shows the features of the MP27631.

Figure 6: Features of the MP27631

Conclusion

In this article, we reviewed the PoE switch power structure and three types of power supply adapters. We also covered MPS power solutions for switches and highlighted the MP3924, MP9572, and MP27631. MPS leads the semiconductor industry with its robust portfolio of products across PSE, switching converters and controllers, and isolation.

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