Most semiconductor vendors embarking on PoE chip development enter with a general background in power management and some particular experience with hot-swap control. However, there are vendors looking to join the field by exploiting their expertise in other, PoE-related areas. For example, National Semiconductor's and Micrel Semiconductor's portfolios include both power-management components and PHYs. For these companies, the goal now isn't to fully integrate the PHY and power-management circuitry. Rather, it's to develop chip sets that will achieve the most useful and cost-effective partitioning and integration of data and power-management functions at the system level.
National Semiconductor is currently developing PSE and PD-side power managers. Integration and partitioning drive development on the PSE side. On the PD side, its chip development is driven by requirements for integration and flexibility. The company expects to produce first silicon about a year from now.
Meanwhile, Micrel plans to introduce a PSE-side chip set with both PHY and power-management functions in the second half of 2004. The chip set will offer an enhanced set of system-level features while lowering overall cost per port. During this time, Micrel is also expected to unveil a PD-side power manager that will integrate a switching regulator for stepdown dc-dc conversion of the 48-V power supply.
Another vendor, Semtech, plans to introduce PSE and PD power controllers as part of a turnkey power-management solution for PoE. In this case, the controllers will complement the company's switching regulators, PWM controllers, and LDOs, which will step down the 48-V dc bus to lower chip-level voltages. Note that other vendors mentioned in this report also offer these types of components. Although a discussion of these ICs is beyond the scope of this article, their performance will certainly be significant for system designers developing PSE and PDs.
For example, the efficiency of stepdown regulators will be a key consideration for some applications given the limited power available to the PDs. Moreover, the task of stepping down the 48-V bus is made more difficult because the PDs are likely to require multiple supply voltages.
Most of the PSE controllers introduced so far provide multiport control. These devices rely on external MOSFET power switches and current sensing resistors. However, chip vendor Supertex plans to offer an alternative to these "ganged" controllers. Supertex describes its first offering as an "n-port distributed PSE" controller. This device provides complete IEEE802.3af functionality for each port, but it also includes an on-chip power switch as well as EEPROM and an I2C interface to store various device parameters and measure operating points.
The company claims that taking a distributed control approach (putting a controller at every port) reduces wiring requirements, saving board space and lowering crosstalk versus that of centralized control schemes based on ganged controllers.
At the same time, this approach enables accurate thermal monitoring of each power switch. In addition, a 100-V rated on-chip regulator will allow the controller to operate directly from the 48-V supply, eliminating external shunt components. This device is slated for introduction in the first quarter of 2004. Following that release, Supertex plans to introduce a device that can serve as either a PD or PSE controller.
BEYOND CHIPS
Much of the focus now is on optimizing the chips and chip-set solutions, yet packaging also plays an important role, particularly as it relates to the integration of magnetic and passive components. In recent years, connector vendors have begun to take the magnetics, capacitors, and resistors used for isolation and signal integrity in Ethernet applications and integrate them into the RJ-45 jack.
According to Molex, the next step will be to integrate the PSE power-management IC into the RJ-45. To this end, the company is working closely with a semiconductor vendor to develop such a connector. It's slated to debut in mid-2004.
Beyond the component-level efforts, which include development of magnetics, circuit protection, and other passives, power-supply companies are working to develop PoE-tailored ac-dc and dc-dc power supplies. (For more on power supply developments, see the Analog and Power Techview in this issue, p. 26.)