Power Electronics

Data Points

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Low-ESR Pulse Supercaps Work at Higher Voltages

AVX has extended the voltage ratings in its BestCap (battery energy-saving technology capacitor) series of low-ESR pulse supercapacitors. The new BestCap electrochemical double-layer capacitors are now available in BZ05 and BZ06 cases with an expanded capacitance/voltage range of 500 mF/3.3 V to 90 mF/12 V with sub-100-mΩ ESR and leakage current in the range 5 to 40 µA. AVX's aqueous polymer chemistry makes BestCap a fully RoHS-compliant, environment-friendly device.

“The BestCap series provides high capacitance, even with short pulse applications, and offers more efficient energy savings in battery circuits than conventional supercapacitors,” said Chris Reynolds, AVX product manager. “The polymer technology eliminates the need for external balancing resistors, while the low ESR results in a high current handling capability, making this an ideal solution for any portable or wireless devices requiring high power availability. The availability of high-voltage ratings vastly expands the number of power management applications that can be addressed.”

The BZ05 package targets pulse hold-up applications from server/ADSL to wireless/electromechanical AMR (automated meter reader), while the BZ06 is a special low-profile device for digital cameras and PCMCIA. Pricing starts at $3.25 in quantities of 10,000. For more information, see www.avxcorp.com.

P-Channel Load Switches Are Rated at 1.5 V

Existing p-channel load switches provide low RDS(ON) values at voltages as low as 1.8 V. As the VGS voltage drops further, the on-resistance of these devices rises rapidly. However, a new series of power MOSFETs from Vishay Siliconix rates RDS(ON) at a VGS of 1.5 V, providing on-resistance values that are about 30% above ratings at 1.8 V. These devices are 100% tested for RDS(ON) at 1.5 V. For some low-voltage applications, these 1.5-V rated devices eliminate the need for level-shifting circuitry.

The first devices in this series are TSOP-6 packaged MOSFETs, the Si3499DV and the Si3495DV. The Si3499DV features a BVDS rating of -8 V and a max VGS of ±5 V. Meanwhile, the Si3495DV features a BVDS rating of -20 V and a max VGS of ±5 V. On-resistance values for these MOSFETs are shown in the table.

Besides offering the 1.5-V-rated load switches in TSOP packages, the company plans to make these parts available in the Micro Foot, PowerPAK SC-70 and SC-75 packages, and in the ChipFET package. Next year, this technology will also be offered in n-channel versions. Additionally, the company plans to offer load switches rated at even lower voltages. For more information, see www.vishay.com.

Monolithic Switching Regulators Offer More Options

Semiconductor vendors are continuing their efforts to develop monolithic switching regulators that are nearly as easy to use as linear regulators. Fairchild Semiconductor's new line of Integrated Switchers combines controller, gate driver and MOSFETs to create synchronous stepdown regulators that are said to be very easy to use.

These switchers operate from a 3.3-V to 5-V input or a 5-V to 12-V input, delivering up to 5 A of output current (see Fig. 1). The 5-V parts (FAN5307, FAN2001, FAN 2011 and FAN2003) are housed in SOT-23s, while the 12-V part (FAN2105) is offered in MLLPs rated for 2 W of dissipation with no derating up to 70°C.

The 5-V rated parts can convert a 5-V supply to 3.3 V with up to 95% efficiency while switching at a fixed frequency of 1.3 MHz. Efficiency is up to 75% or 80% at lower values of output voltage. These ICs are expected to find application in large form-factor cell phones and PDAs, as well as in small hard disk drives.

In quantities of 100,000 pricing will be approximately $0.50 per chip. The bill of material costs for the external capacitors and inductor is expected to total about $0.10 to $0.20. Compare that with a 1.5 A LDO that converts 5 V to 3.3 V with about 60% efficiency and costs about $0.15 to $0.20 per chip. The FAN2001, FAN2003, and FAN2105 are now sampling. For more information on these devices, see www.fairchildsemi.com.

Meanwhile, Maxim Integrated Products is developing a series of integrated MOSFET stepdown regulators that offer the digital designer switchmode efficiency using a simple layout that the designer can copy. The first device in the series, the MAX8566 is a 10-A buck regulator with on-chip 10-mΩ MOSFETs. Designed to operate from 2.25-V to 3.6-V supplies, the regulator can run off of both 3.3-V and 2.5-V supply rails. Regulator output is an adjustable 0.6 V to 0.85xVIN with 1% accuracy over load and line. The input-voltage range and the output-voltage range extend lower than some competing monolithic devices in the same output-current range.

Housed in a 5-mm × 5-mm 32-pin TQFN, the regulator switches at an adjustable frequency ranging from 250 kHz to 2.4 MHz, enabling use of small external components.

Operating from a 3.3-V input and switching at 1 MHz, the MAX8566 can produce a 2.5-V output with an efficiency exceeding 95% at medium loads. At the rated 10-A output, the efficiency will be about 93% for similar input- and output-voltage conditions and switching frequency.

Other features of the regulator include programmable soft-start, REFIN for tracking, monotonic startup, and a syncout that drives a second regulator 180 degrees out of phase. In quantities of 1000, unit pricing is approximately $3.65. For more details, see www.maxim-ic.com.

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