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Posted on 10 July 2019

Wide Input, Low Output POL Regulators

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Delivery of Benchmark Efficiency With High Density

Capable of handling input voltages as wide as 1.5V to 16V, the second generation integrated point-of-load (POL) regulators are designed to deliver output voltages from 0.7V to 12V at peak efficiency greater than 96%. Thanks to programmable switching frequencies up to 1.5 MHz, this voltage regulator shrinks size and cost as well to achieve a new high in power density.

By Cecilia Contenti, International Rectifier, El Segundo, California

 

Whether it is servers, data storage facilities or Netcom applications, the need to save power in these equipments is surging vigorously. Because lower dissipation means simpler thermal management and lesser infrastructure cost, the efficiency bar in these products has been further raised by international regulatory agencies and OEMs alike.

While there are many sources that contribute to power consumption in these products, DC-DC converters and voltage regulators used to power various electronic loads in these applications consume about 25-30% of the total power dissipation. Hence, the pressure to build more efficient power supplies with high density is even greater.

Consequently, new and advanced power management solutions are needed to cope with the new challenges. As a result, to overcome the limitations of traditional discrete and monolithic designs, a novel integrated solution has been developed that combines the best of both the worlds. While it simultaneously improves efficiency and cuts size and board space dramatically, it also offers a single rail design to convert a wide input voltage range into a low voltage output. Traditionally, high input to low output DC-DC voltage converters require two stages.

To raise the efficiency bar, this integrated solution incorporates three optimized power components-synchronous buck controller, control FET and sync FET- to minimize conduction and switching losses. In addition, the three power components are cleverly co-packed to eliminate interconnect and packaging parasitic for higher frequency of operation. Plus, it uses pulse-width modulated (PWM) voltage mode control with external compensation to provide good noise immunity and flexibility in selecting inductor values and capacitor types. And, lastly, the design is scalable.

Labeled SupIRBuck, the integrated point-of-load (POL) voltage regulators were first released in November 2007 (SupIRBuck Gen1 family). Ongoing improvements and enhancements have resulted in a second generation family or SupIRBuck Gen 2 integrated POL regulators that surpass the efficiency and density of first generation to set a new performance benchmark. And, thereby, promises to boost efficiency in servers, data storage equipments or similar products by about 5 to 6% with increased density over previous solutions. Gen2.1 devices represent an upgrade to Gen2 parts launched early last year (Figure 1).

Second generation Gen2.1 POL regulators provide an upgrade path to Gen2 parts launched in early 2009

To achieve dramatic improvements in efficiency and density simultaneously across light and heavy loads, the integrated Gen2 POL regulators have been redesigned with new advanced CMOS engine capable of handling switching frequencies up to 1.5MHz, high performance floating gate drivers and integrated bootstrap synchronous MOSFET such as mono-FETKY (Figure 2). For improved transient response, high bandwidth (25MHz) high gain error amplifier is used in this design. In addition, circuit techniques have been incorporated to improve the accuracy for current limit and reference voltage, while the standby current has been reduced significantly. For instance, maximum stand-by current is specified at 500 µA.

Block diagram for Gen2 SupIRBuck family

For higher density and easy upgrade, all members of the second generation family are housed in the same thermally enhanced low profile 5 x 6 mm QFN package. Additionally, to lower the overall onresistance (RDS(on)) of the sync FET, the interconnect resistance of the package has been minimized.

New Efficiency Benchmark and More

The second generation SupIRBuck Gen.2.1 POL regulators offer output currents up to 12A with efficiency as high as 96% from low to high load range. In essence, these new generation POL regulators are designed to provide a flat efficiency curve across a wide load variation. At the low end, it can deliver output current as low as 2A without compromising performance. While optimized for 12V input voltage, the high electrical performance is maintained at input voltages like 9.6V, 5V and 3.3V. Also, since the footprint is common for all members in this family, it provides design flexibility that permits easy cut-and-paste layout for fast time to market.

Besides providing pin compatible current options from 2A to 12A, the Gen2.1 integrated POL regulators also bring new functions like power good (PGOOD) output for over voltage and under voltage detection, shorter dead-time to reduce power losses and more precise over current (OC) limit. The PGOOD output detects over voltage and under voltage conditions and provides a feedback that can be used by appropriate control logic to shutdown the system or control a second rail. In addition, the PGOOD signal for trackers devices offer tracking capability. And the lower maximum RDS(on) of the sync FET improves OC limit accuracy.

The maximum RDS(on) is 6.9mOhms for IR3840W LFET, which is about 14% lower than the previous generation. Similarly, other members like IR3841W and IR3842W offer 10.7 mOhm and 19 mOhm, respectively. Additional features include pin compatible solutions for 2A, 4A, 8A and 12A units, small footprint (5 x 6mm) and low height (0.9mm), 1% accurate 0.7V reference voltage, programmable hiccup current limit, programmable soft start, enhanced pre-bias start up, thermal protection, enable pin with voltage monitoring capability, and -40°C to 125°C operating junction temperature range.

To illustrate high efficiency capability of this new POL family, measured efficiency results over wide load variations for a 12A unit (IR3840W) are depicted in Figure 3. The switching frequency used here is 600kHz, while the input voltage is 12V. The test data shows that for 5V output the peak efficiency is greater than 96% for load current variations from 4A to about 9A. And drops to 95% at 12A load current. Similarly, on the lower side, the efficiency is 95% at 2A output current. In short, the efficiency curve is flat, which is an important factor in applications that require high efficiency across a wide current range rather than at a single point. Even as the output voltage drops below 2V, the efficiency performance remains over 90% across a wide load range. The end result is energy savings and a lower operating temperature requiring a very simple thermal management solution. In other words, Gen2.1 POL regulators are designed to deliver full current rating with no airflow and without a heat sink. All this translates into high reliability levels for the second generation SupIRBuck regulators.

The SupIRBuck Gen2.1 POL regulator efficiency is high and remains flat across a wide load range.

By comparison, at 600kHz operating frequency, the Gen2.1 efficiency is about 5% to 7% higher than Gen1 devices. However, Gen2.1 devices offer programmable switching frequencies up to 1.5MHz. Hence, for applications where density matters, Gen2.1 POL regulators can be switched at frequencies as high as 1.2MHz. to cut the size of external passive components while maintaining high efficiency. This is demonstrated in Figure 4, where Gen2.1 unit IR3841W switching at 1.2MHz is compared with similar device operating at 600kHz, as well as a Gen1 member (IR3821). Here, the input voltage is 12V and the output is 1.8V for all the three regulators. It is observed from this figure that designers have the flexibility to either achieve benchmark efficiency at 600kHz or to operate at 1.2MHz or above and shrink the size by about 20% without trading off efficiency performance.

Comparing efficiency performance between Gen 2.1 and Gen 1 devices

Design Flexibility

Often current or power requirements change during the design process. Traditionally, these changes require new parts with new layout and design. To simplify such implementation, SupIRBuck Gen2.1 offers pin compatible common footprint for 2A (IR3843W), 4A (IR3842W), 8A (IR3841W) and 12A (IR3840W) devices. Thus, by simply changing the part number (PN), Gen2.1 units adapt quickly to changing current or power requirements. In short, the flexibility afforded enables easy upgrade and cut and paste layout for fast time to market.

Figure 5 presents efficiency performance for four different devices of the Gen2.1 family; namely IR3840W, IR3841W, IR3842W and IR3843W. For the same input and output voltages and load current, it is seen that the efficiency performance for the four parts varies slightly. Consequently, by exploiting the pin compatibility and the common footprint of these devices, the user can optimize performance versus cost for current levels up to 8A. Also, since most of the design parameters are programmable, including frequency, soft start time and hiccup current limit, it permits the designer to customize the design parameters based on specific applications.

Efficiency versus load Current for 2A, 4A, 8A and 12A SupIRBuck Gen2.1 POL regulators

In summary, the efficiency of second generation SupIRBuck POL regulators has been significantly enhanced with simultaneous reduction in size. In addition, Gen2.1 regulators offer more features and programmability. Plus, for easy upgrade and fast turn around, these devices maintain the same 5 x 6 mm QFN package of Gen1.

 

References:

1. “Saving Energy Translates Into Lower Total Cost of Ownership for Data Centers”, by Tim Phillips, VP, International Rectifier, Enterprise Power Business Unit.

 

 

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