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Microchip Technology Advances Power Management with 500 mA Synchronous Buck DC/DC Converter

Device converts battery or bus voltage to its system requirement, operates over many I/O conditions.

The manufacturer says...

ChipCenter's Paul O'Shea says . . .

Microchip Technology announced a 500 mA DC/DC synchronous step-down converter that operates over a multitude of input and output conditions. This gives designers an efficient method of transforming battery or bus voltage to meet their system requirements. Used in applications such as cellular phones, PDAs, digital cameras, and USB-powered devices, the MCP1601 operates in three modes and automatically switches among them to follow a maximum-efficiency curve for the given input/output (I/O) condition. The three operating modes include pulse-width modulation (PWM), for normal medium-to-high load conditions; pulse-frequency modulation (PFM), for light or no-load conditions over an extended time; and low-dropout mode (LDO), for cases when the input approaches the output voltage. This DC/DC converter also has integrated safety features such as overcurrent, overtemperature, and undervoltage lockout (UVLO) protection to safeguard the converter circuitry. Additionally, the device has an externally controllable shutdown mechanism to minimize the drain current during system inactivity. Moreover, the MCP1601 can be implemented with a complete ceramic capacitor solution, eliminating the need for larger tantalum caps. "The MCP1601 provides a very efficient and cost-effective method of converting battery or bus voltages to a desired lower voltage," said Jim Mack, marketing manager for Microchip's Analog and Interface Products Division. "In addition, it offers several self-protection mechanisms that provide an additional level of security for our customers." The input voltage on this device ranges from 2.7 to 5.5 V. The output voltage range is from 0.9 V to as high as VIN for the input voltage, while the shutdown current is typically less than 0.1 µA. It has a load current capability of up to 500 mA (continuous) and will operate at 100 percent duty cycle or LDO mode when the input voltage approaches the output voltage. The UVLO voltage ranges between 2.4 and 2.7 V. The MCP1601 is available in an 8-pin MSOP, with pricing set at $1.70 for 1000-piece units. Samples and volume-production quantities are available today. For additional information or pricing on these devices, contact any Microchip sales representative or authorized worldwide distributor, or visit www.microchip.com. Microchip Technology Tel: (480)792-7668 Web: www.microchip.com

The MCP1601 is a 500 mA, DC/DC synchronous converter aimed squarely at the portable, battery-based market, but it is still appropriate for changing a bus voltage from 5 V to 3.3 V or from 3.3 V to 2.5 V, and for those systems that have multiple buses with the 500 mA load limitation. This also is Microchipıs first synchronous buck converter. A synchronous buck converter uses the high-side p channel to charge the system, and uses an n-channel diode that lets the current free-wheel back from the inductor. It uses another transistor that turns on very quickly and returns the current to ground. The converter integrates both components on the same chip, which increases the efficiency. The efficiency is important to control heat generation. The major advantage of the switcher is its high efficiency and its ability to keep the power down that is otherwise wasted in the converter. It replaces low-dropout regulators in some simple systems that are very inefficient. The MCP1601 operates in three operating modes—pulse-width modulation (PWM), pulse-frequency modulation (PFM), and low-dropout (LDO). The PWM is for high-current or full-load conditions to maximize efficiency. The PFM mode is for a very light load or no load that you want to wake up occasionally and supply current to the circuit. Finally, the LDO mode is for full-on, and is meant to track a lithium-ion battery from a full charge to minimum voltage and still provide a constant output. The 1601 also has some fairly common safety features to control overtemperature, undervoltage lockout, and overcurrent. I was impressed by its shutdown current, which is an extremely low 0.1 µA—much lower than several other converters on the market. Microchip decided to integrate the oscillator, which is good news for you because it requires no external components. The company says they picked the 750 kHz frequency after talking with customers to determine the best frequency to optimize between the speed of the switching edges and the operating frequency. Itıs an important factor in the design because 750 kHz is fast enough to keep the efficiency up, but not too fast so the switching edges cause radiated and conducted EMI. Another reason the company chose 750 kHz was to minimize the external inductor and capacitor sizes needed for the buck topology. However, the MCP1601 can be synchronized to an external oscillator, but it must be greater than 850 kHz and less than 1 MHz. Another feature that could be easily overlooked is the converterıs ability to provide stable operation with ceramic capacitors. This is for those designers that donıt like using those larger, leaky tantalum capacitors. However, lower equivalent series resistance (ESR), which can occur when you use a ceramic cap, can switching problems. Microchip ensured that this design can operate with the ceramic caps and not cause a problem with switching by providing examples of what works best. For example, with a 10 µH inductor and 10 µF capacitor you can keep the output ripple less than a very low 8 mV. The external components required include the capacitor, the inductor, and some resistors. So if you are in the normal output operating range from 1.2 V and up, the MCP1601 needs only a pair of resistors to set the voltage at the output. To get down from 1.2 V to 0.9 V requires one additional resistor. Microchip says they are very proud of the 8 mV output ripple when the system is operating in the normal PWM mode. Additionally, with a PWM switcher you do need an inductor as opposed to a capacitor. If you use an inductor, you get very high efficiency. The trade-off, of course, is noise. For example, this MCP1601 has an efficiency of 92% efficiency or better in most cases, but it does radiate. The quiescent current is about 120 µA in the PWM mode when the MCP1601 is operating at very high current. I couldnıt find the quiescent current for the PFM mode, but I would expect that it would be less than the PWM quiescent current. Datasheet

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