Archive | Feedback

Vishay Siliconix 600-mA DC/DC Step-Down Converters Enable Output Voltages as Low as 0.4 V for Ultra-Small Applications

The manufacturer says . . .

ChipCenter's Paul O'Shea says . . .

Three new 600-mA synchronous buck converter ICs -- devices that will help to prolong the run-times provided by single-cell Lithium-ion batteries -- were announced today by Siliconix incorporated, an 80.4%-owned subsidiary of Vishay Intertechnology, Inc. The new high-performance step-down converter ICs, which combine industry-best specifications for lowest output voltage and highest switching frequency with the smallest solution footprint, are intended for end products including cell phones, PDAs, digital cameras, MP3 players, portable scanners, LCD modules, and dc-to-dc converter modules. The three devices released today convert 2.6-V to 6-V input voltages to output voltages as low as 0.4 V -- a record-breaking capability that prolongs battery life. A maximum PWM switching frequency for the Si9174, Si9175, and Si9176 of 2 MHz sets another record -- and greatly reduces output capacitor and inductor size. With integrated power MOSFETs and only six external components -- one inductor, three capacitors, and two resistors -- the Si9174, Si9175, and Si9176 allow designers to create the industry's smallest complete step-down converter solution. As such, the new Vishay Siliconix ICs allow manufacturers to cut component and assembly costs, in addition to enabling design of more compact and efficient electronic systems. All three new ICs feature 100% duty cycle control for very low dropout, as well as selectable PWM (pulsewidth modulation), PSM (pulse-skipping mode), and Auto Mode (for automatic shifting between PWM and PSM) to ensure efficient operation throughout the entire load range. The Si9174 and Si9175 can be synchronized to a 13-MHz external oscillator to reduce system noise in cell phones. The Si9174 features a DAC input for fast dynamic output voltage adjustments from 0.4 V up to the input voltage, while the Si9175 and Si9176 feature a fixed output voltage down to 1.2 V set by external resistors. Integrated protection features include thermal shutdown, undervoltage lock-out, and overcurrent protection. The three converters are rated for operation over the industrial temperature range of -40 to +85 degrees Celsius and are available in an MSOP-10 package or a leadless MLP33 package measuring just 3 mm by 3 mm. About Siliconix Siliconix, a company of Vishay Intertechnology, Inc., is a leading manufacturer of power MOSFETs, power ICs, and analog switches for computers, cell phones, fixed communications networks, automobiles, and other electronic systems. With 2001 worldwide sales of $305.6 million, the Company's facilities include a Class 1, six-inch wafer fab dedicated to the manufacture of power products in Santa Clara, California, and an affiliated Class 1, six-inch wafer fab located in Itzehoe, Germany. Power products are also manufactured by a subcontractor in Japan. Analog switches, analog multiplexers, and low-power transistors are fabricated by subcontractors in Dresden, Germany, and in Beijing, China. Assembly and test facilities include a company-owned facility in Taiwan, a joint venture in Shanghai, China, and subcontractors in the Philippines, China, and the United States. Vishay Siliconix, 2201 Laurelwood Road, Santa Clara, California 95054. Email: info@vishay.com, Vishay Web Site

This part targets portable devices that use Lithium Ion batteries, including cell phones and PDAs. Many of these cell phones run with custom ASICs that have power management circuits. However, the power requirements of the cellphone chipsets are changing rapidly, as such the custom ASICs in these devices need to be upgraded. For example, a chip that used to run at 2.8 V now runs at 1.5 V. Thatęs the market Vishay is servicing with these DC converters. The chips will also be suitable for parts that arenęt portable and need to convert from 5 V down to 3.3 V - at high efficiency. Examples include set top box power supplies, especially those that are getting smaller. The input voltage for these buck converters is limited to 6 V and the output can go down to 0.4 V. The low 0.4 V is needed for powering CDMA type phones that must ensure that they have power supplied to the power amp even at a very low voltages. For example, the Si9174 has a dynamically addressable voltage control (DAC) input that regulates the output voltage and can go down to 0.4 V. The Si9174 can dynamically address the output voltage according to the voltage present on the DAC pin. The output voltage is regulated to the same voltage of the DAC pin through a resistor divider. An important feature of these buck converters is the frequency. They have a 2 MHz frequency, which means you can use a very small inductor and capacitor for the rest of your design. Additionally, and of no minor importance, is the very high efficiency (up to 96%) of the converters, which is important for conserving battery life. This is a very small design that only needs 6 external components. It doesnęt need a Schottky diode, however, it does require one inductor, two resistors and three capacitors. It works with a 2 uH inductor and that means it works with most of the available parts in the marketplace, so you donęt have to change inductors. If you look at the Vishay demo board you will notice that the inductor takes up most of the space on the board. Vishay says they are working with other companies to get the inductor part even smaller. The trio of buck converters from Vishay are available in a 10-pin MSOP and an MLP-33 package, with a difference in power. One had 481 mW and the other had 915 mW. That seemed significant. However, Vishay tells me that it is not die related but is a function of the package. In the MLP-33 you gain the space of no outside pins but you pay for that with increased power - so itęs a tradeoff. The Si9174 and Si9175 can be synchronized to an external oscillator but the Si9176 can not be synchronized to an external oscillator. The oscillator is an option for applications to reduce the noise. Though applications like the PDA donęt need the external oscillator, so the Si9176 makes it easier to use for PDAs. Another interesting aspect about these converters is their capability to be used in different modes, depending on the load. They can be used in Pulse Width Modulation (PWM), Pulse Skipping Mode (PSM) and auto mode. The auto mode automatically switches between PWM and PSM as the load current changes. At low loads it uses PSM because it has the highest efficiency. From about 150 mA to 170 mA the part switches to PWM because at higher loads the PWM provides higher efficiency. So if you set the part to auto mode you can have high efficiency for the whole operation. The efficiency can even be higher than 90%, starting with as low as about 10mA load and this can extend the battery life. In the PWM mode it has a 2 MHz synchronous rectification for load currents up to 600 mA. In PSM the frequency is reduced to transfer only the energy needed by the load. Just as important is the capability to set the converter in either PSM or PWM, which would be useful if your application didnęt use it with less than 350 mA. This load would have more stability if it were used only in the PWM mode. These chips should be successful because many of the competitors have larger chips and donęt offer the high frequency with small inductor size. You may find a couple solutions that offer the high frequency and even the small size, but take a closer look at the efficiency and you'll find it probably wonęt be as good over a wide range of loads. Samples and production quantities of the Si9174, Si9175, and Si9176 are available now with lead times of six to eight weeks for larger orders. Pricing for U.S. delivery only in 50,000-piece quantities starts at $1.30. Data Sheets: Si9174 Si9175 Si9176

Analog Main | Product of the Week | Columns | Editorial | Tech Notes

		Click here to get your listing up.