New Standards Achieved in Integrated Switching Regulator Design

Designers of electronic systems and products have known for a long time that internal power rails really cannot be seen as independent of the equipment function. Of course, product performance can rely heavily on voltage rail accuracy, noise level, and response to load transients, but operating speed and system power consumption can also be optimized by dynamic control of power rails generated from high-efficiency switching regulators. This has become of prime importance with the Internet of Things (IoT), for example, where more performance is being packed into remote sensors and actuators with the need to operate over a wide input voltage range while limiting power draw to extend battery life. At the same time, products are expected to be smaller, run cooler in operation, be more reliable, and, of course, have lower cost.

In high-performance systems, every stage of the power conversion from the supply to the individual loads needs to be assessed and optimized. In such complex systems with multiple supply voltage rails, Point of Load (PoL) converters – a type of DC/DC converter – are often the best solution, providing precise voltage rails where needed, ideally with a wide input range, high efficiency, and programmable outputs. ‘PoLs’ as complete modules have existed for many years, but many are derived from the Telecoms market with very high output currents at very low voltages and a very narrow supply voltage range. What the IoT industry wants to see is a PoL voltage regulator that is low-cost, flexible, efficient, small, and compatible with automatic pick-and-place placement systems and industrial environments - in particular the 24V supply voltage which is typical for industrial automation.

The RPX-2.5 integrated regulator has a wide input range of 4.5 to 28V (24V + 15% tolerance) and a 1.2 to 6V adjustable output. The 2.5A rating is conservative, and more current is available to supply high start-up current applications. Efficiency peaks at 91% with a 12V input and 5V output, with this high value maintained down to just 3% load for applications where ‘sleep’ or intermittent loads are possible. Effective power management is a key benefit.

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Depending on the input/output voltage combination, full output power is guaranteed at up to 85°C ambient with a specified PCB size and copper weight without a heatsink or forced air cooling. This outstanding performance is achieved in a small package with ‘Flip-Chip-On-Leadframe’ (FCOL) technology, which gives very low thermal resistance from the control IC junction to the PCB pads. The product is also over-molded, forming a MSL3-rated leadless QFN (Quad Flat No-lead) package with full environmental protection.

Manufacturing of the part is fully automated with an integrated shielded inductor which, along with the reduced parasitic inductances of the compact design, gives an inherently low EMI. Output protection is comprehensive as well, with immunity to short-circuits, output over-current, and over-temperature conditions. These features contribute to new regulator standards in reliability and performance.

For optimum flexibility, the output voltage is presettable externally with a resistor chain connected to the ‘FB’ pin. This gives the user the option to choose the optimum output voltage as well as to implement ‘remote sensing’ for the best load regulation and to add a ‘speed-up’ feed-forward capacitor (CFF in Figure 2) to improve response time to overcurrent transients. Alternately, CFF can be omitted, and additional output capacitance added to increase the tolerance to overcurrent transients. User selection of output voltage also keeps inventory costs low, with just one part covering multiple applications (1.8V, 3.3V, or 5V with one part, for example).


This can be taken one step further with dynamic adjustment of the output voltage under external control. There are many applications, especially in IoT, where processor clock speed and supply voltage can be traded-off for optimum performance and power consumption. For example, a microcontroller running at 3.3V/16MHz consumes typically 30mW, but the VCC voltage cannot be reduced below 3.2V without affecting performance. If the µC is inactive (e.g., waiting for input), the clock frequency can be reduced to 1MHz, reducing the consumption to just 6mW (20%). However, at a 1MHz clock frequency, the supply voltage range is much wider and can be reduced to 1.8V without affecting functionality.

Implementing this reduced supply voltage additionally drops the consumption further to only 1.2mW (4% or a 25x reduction compared with full performance operation), making it within the range of many energy scavenging techniques (Figure 3). This adaptive supply voltage feature is easily implemented with the RPX-2.5 DC/DC converter with a connection from its FB pin to a microcontroller I/O pin, allowing the µC to switch in different values of resistors and adjust its own supply rail.

The RPX-2.5 needs an input capacitor to function correctly, but this can be a small 10µF MLCC type. A 47µF electrolytic type in parallel with a ripple current rating of 1.25A or higher is recommended for high dynamic output load applications, but there will often be sufficient capacitance on the power supply output already for many users. For compliance with EN 55032 class B, a series input inductor can be added.

Similarly, output capacitors are required with values dependent on output voltage and loading. Allowing users to add input and output capacitors only where needed, with the size and voltage rating optimized for the application, yields an overall smaller and lower-cost solution compared with fixed internally fitted capacitors, which would have to be rated at the highest possible input and output voltages allowed in the data sheet. Output capacitors can also be fitted in the optimum position, adjacent to the microcontroller power pins, for example. This flexibility in regulator design is a significant advantage.

Often PoLs need to be able to provide peak power levels for highly dynamic loads such as a GSM module in transmit mode. One solution is to dimension the converter so that it is rated for the highest peak current, but this often comes with the disadvantage of poor efficiency at low output load – on the other hand, if the PoL has a high short-duration peak over-current rating, it can be smaller, more efficient, and lower cost. The RPX-2.5 power module provides this feature with a 30% ‘boost’ capability to 3.2A or more for up to five seconds - more than enough time to allow high power data transmissions or high start-up currents. Reliability is not compromised though – the part has an MTBF of 400M hours at 25°C according to the Telcordia reliability guide SR-232.

For even higher continuous current demands, the RPX-4.0 offers up to 4A output in the same compact form factor, making it ideal for applications where peak performance must be sustained without relying on short-term boost capacity. It complements the RPX-2.5 by providing designers with more headroom while maintaining excellent thermal behavior and efficiency of up to 87%.

With its wide input and output ranges, the RPX-2.5 finds applications in many areas. Typically, this voltage regulator can be used with 24V industrial automation supplies with +15% tolerance to provide 3.3V or 5V to control boards. The product’s small size opens up other possibilities, for example, integration within a connector to drop 5V to 3.3V for a sensor. The RPX-2.5 integrated regulator can also be used in automated test equipment, medical and imaging equipment, high density power systems, and many more, including, of course, IoT. For those searching for RECOM Regulators, the RPX-2.5 is a leading example of innovation.

An evaluation board RPX-2.5-EVM-1 is available from RECOM. The board allows selection of popular output voltages, and the remote sense and under-voltage lockout functions can be exercised and evaluated. Filtering is included for compliance with EN55032 class B, but positions are provided for experimentation with alternative components for optimum EMC performance for operating conditions and budget. The board provides the appropriate thermal design for the full power performance of the RPX-2.5 to be evaluated.

Samples and OEM pricing are available from all authorized distributors or directly from RECOM.