As bandwidth continues to increase, deregulation and competition in wired and wireless infrastructure telecommunications systems are driving the need for low-cost equipment solutions. The ever-increasing challenges to be addressed in the power management requirements of telecom equipment have increasingly required designers to be able to provide power for a wide variety of digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and microprocessors. Provide more voltage rails. In short, power management solutions are required that can generate more different voltages and higher currents more efficiently and with reduced noise in a smaller space. Plus, if those requirements weren’t challenging enough, the solution had to be low cost, which is, I’m afraid!
Deploying access equipment closer to users requires smaller accessories (pads and mounting holes) that must be able to withstand harsher environments. Because the space of the central office is very small, the infrastructure equipment will be designed to be more miniaturized. Factors driving the development of power management products are form factor, thermal management, cost, and electrical performance (voltage regulation, transient response, and noise generation). This article will give you a basic understanding of the evolution of on-board power systems and how the latest generation solutions achieve higher performance and lower cost in smaller packages.
Some telecom OEMs insist on using the traditional wide input voltage specification of 36V to 75V with an input transient voltage of 100V. To meet these requirements, the power industry has introduced semi-regulated IBAs (see Figure 4). The main difference between the semi-regulated IBA and the unregulated IBA is that the semi-regulated IBA regulates the output voltage to around 10V if the input voltage exceeds the range of 55V to 60V. The disadvantage of this approach is that the isolated power module must increase in size to accommodate the voltage regulation circuit, and its efficiency will decrease when the input voltage exceeds 55V.
Telecommunications systems typically have a nominal input supply of 48V and can withstand transients of up to 100V. Most power converters on the market today cannot tolerate transients above 60V. Therefore, designers must implement expensive clamping circuits to reduce the transient to a usable voltage. This additional circuitry in the form of TVS diodes or transistors adds both cost and valuable PCB real estate.
The new LM5017 100V synchronous buck simplifies such high voltage designs while reducing PCB footprint and component count. The LM5017 has a wide operating input voltage range of 9V-100V without clamping circuits. It is the industry’s first 100V converter with integrated high-side and low-side FETs, all in a compact 4mm x 4mm LLP-8 package. Synchronous rectification offers higher efficiency and unmatched ease of use as no external FETs or freewheeling diodes are required. Figure 1 shows a typical application diagram of the LM5017 as a 100V synchronous buck regulator.
Improving the flexibility and reliability of telecom equipment power management when using high voltages
Figure 1: The LM5017 as a high-voltage synchronous buck regulator.
Further simplifying designs with the LM5017 is the device’s constant on-time (COT) control topology. With no error amplifier or compensation to limit the bandwidth, COT devices have lightning fast response to line and load transients. And because no loop compensation is required, the design requires fewer external components, reducing the bill of materials, component count, and overall solution cost.
Improving the flexibility and reliability of telecom equipment power management when using high voltages
Figure 2. Simplified secondary-side control application diagram.
Telecommunications systems that require isolation face a similar set of challenges. With the increasing popularity of secondary-side digital controllers directly powering loads, there is an increasing need for bias supplies that can withstand 100V transients. This type of system is shown in Figure 2. Flyback solutions supporting 100V in the market today require a large number of external components and more PCB space than they should. Figure 3 shows an example.
Improving the flexibility and reliability of telecom equipment power management when using high voltages
Figure 3: Competing flyback solutions for isolated secondary-side bias supplies.
FET integration, along with continuous conduction mode operation, provides the flexibility to use the LM5017 as an isolated power supply with a transformer or coupled inductor. Additionally, an adjustable switching frequency up to 1MHz allows the size of the magnetics to be minimized. The result is the industry’s smallest primary-side and secondary-side biased 100V solution, requiring 50% less PCB footprint than leading competitors. Figure 4 shows an application diagram using the LM5017 as an isolated bias supply, which requires fewer external components than competing products.
Figure 4: An isolated bias supply solution based on the LM5017 requires only 13 components.
Of course, the advantages of the LM5017 are not limited to the telecom market. The wide voltage range and ease of use make it ideal for many industrial applications as well as automotive battery management, smart grid, solar and more. The LM5017 supports WEBENCH®, making high voltage point-of-load design easier than ever.