DC-to-DC Converters

As electronic circuits proliferate and increasingly lower voltages are used to power increasingly higher performance digital ICs, the challenges to dc-to-dc converters increase, as well. Operating at the highest frequency reduces the number of input filters for dc-to-dc converters and the value of the external components including output inductor and capacitor. This is increasingly important to support low-power digital signal processors (DSPs) and microcontrollers (MCUs) in portable electronics. High-current point-of-load (POL) power can require different functions, as well as sophisticated protection circuitry. Application requirements can include low quiescent current, a soft-start function and low current output in the 100's of mA for portable applications to 80A or more for computing and communication equipment. Of course, for portable products, a small package is an obvious requirement. Here are two products that address portable products and one that targets POL requirements.

Low Power DC-to-Dc Converter

Operating at 2.25 MHz, Texas Instruments incorporated TPS62290 step-down converters deliver 1A in A2 × 2 mm 6-lead SON package. Powered by a single-cell lithium-ion (Li-Ion), three-cell nickel metal hydride (NiMH) or three-cell alkaline batteries with an input voltage range of 2.3 to 6V, the units regulate output voltages down to 0.6V with ±1.5 percent accuracy. Operating with a 15 µA quiescent current, the converter enters a power-save mode during light-load operating conditions and maintains efficiency up to 95 percent over the entire load current range. In the shutdown mode, the current consumption is less than 1 µA. Pulling the MODE pin high implements fixed-frequency pulse width modulation (PWM) operation for low-noise applications. The high-efficiency and low current consumption provides extended battery life in Bluetooth headsets, cell phones and other Li-Ion battery-powered applications.

http://rbi.ims.ca/5406-589

Configurable Dual-Phase PWM Control ICs

High-current point-of-load (POL) buck converters in networking, computing and communication systems require a different approach than portable products. Two dual-channel synchronous buck control ICs from International Rectifier address these applications. The IR3622MPbF targets 12V single input supplies and the IR3622AMPbF supports 5 and 12V requirements. Providing a programmable switching frequency up to 600 kHz, the units can be configured to deliver up to 80A from a single output or to support two independent outputs. Operating in the single output mode reduces the output ripple voltage. Running 180 degrees out-of-phase, the independent channels reduce the input capacitance requirements. Two independently programmable soft-start functions allow different configurations of system-level sequencing of the output voltages for system level start-up. The 32-lead 5 × 5 mm MLPQ-packaged unit's protection features include selectable hiccup or latched current limit, pre-bias start-up, thermal shutdown protection and under- and over-voltage protection.

http://rbi.ims.ca/5406-587

Small Synchronous Buck Converter

Fairchild Semiconductor's FAN5350 switching voltage regulator delivers a fixed 1.82V from an input voltage supply of 2.7 to 5.5V. The 3 MHz 600 mA synchronous buck converter has 16 µA quiescent current. Switching at 3 MHz allows the use of small chip inductors (1µH) to achieve low ripple. According to Peter Khairolomour, technical marketing manager at Fairchild, "Transient response is becoming more and more critical as processor voltages continue dropping and load regulation requirements are tightening." During a load transient swing of 0 to 300 mA, the regulator's output fluctuates less than 20 mV. Promoted as the smallest buck converter on the market, package options include a 6-lead 3 × 3 mm Molded Leadless Package (MLP) and a 5-bump 1.00 × 1.37 mm Wafer Level Chip Scale Package (WLCSP). The small dc-to-dc converters target cell phones, media players, GPS devices, Bluetooth headsets and other single-cell 2.7 to 5.5V lithium-ion-powered portable applications.

http://rbi.ims.ca/5406-588