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Switching regulator integrates watchdog timer

Posted: 19 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:switching regulator? automotive applications? telecom systems?

Linear Technology Corp. has unveiled the LT3641, a dual channel, current mode step-down switching regulator with a power-on reset and watchdog timer. Its 4V每42V input voltage range with 55V transient capability makes it suitable for load dump and cold crank conditions commonly found in automotive applications that require constant output regulation even with input transients as high as 55V.

The LT3641 uses a dual channel design with a high input voltage (4VIN每42VIN, 55VIN transient capability) nonsynchronous channel, which delivers 1.3A of output current combined with a lower input voltage (2.5VIN to 5.5VIN) synchronous channel, delivering up to 1.1A of continuous output current. Although the part allows separate inputs for each channel, most applications will use the output of the high voltage channel to power the lower voltage channel, offering dual outputs while optimizing efficiency and switching frequency. For example, using a nominal 12V input and a 2MHz switching frequency, the LT3641 can deliver a 3.3V output at 600mA with 85 percent efficiency via its high voltage channel and a 1.8V output at 800mA with 90 percent secondary conversion efficiency via its lower voltage channel.

The integrated microprocessor supervisor functions support high reliability applications such as automotive electronic control units. The LT3641 includes one power-on reset timer for each channel and one common watchdog timer. The reset and watchdog timeout periods are independently adjustable using external capacitors. Tight accuracy specifications and glitch immunity ensure reliable reset operation of a system without false triggering. The LT3641 implements a windowed watchdog timer monitoring for WDI falling edges grouped too close together or too far apart.

According to Linear, the LT3641's switching frequency is user programmable from 350kHz每2.5MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. Similarly, its low minimum on-time enables it to offer high switching frequencies even with high step-down ratios. For example, even with inputs as high as 35V, it can deliver 3.3V and 1.1V outputs using a 2MHz switching frequency, allowing it to avoid critical frequency bands such as AM radio while minimizing the size of external components. The LT3641 can deliver output voltages as low as 1.26V on its high voltage channel and down to 0.6V on its low voltage channel, enabling it to power the latest generation of microprocessors. Its low ripple burst mode operation reduces quiescent current to only 290?A with less than 15mVPK-PK of output ripple, making it suitable for applications such as automotive or telecom systems, which demand always-on operation and optimum battery life. The LT3641's 4 x 5mm QFN-28 (or TSSOP-28) package and high switching frequency keeps external inductors and capacitors small, providing a very compact thermally efficient footprint.

The LT3641EUFD and LT3641EFE are priced starting at $3.58 each for 1,000 piece quantities. The LT3641IUFD and LT3641IFE are tested and guaranteed to operate from a -40∼C 每125∼C operating junction temperature and are priced at $4.02 each in 1,000 piece quantities. All versions are available from stock.

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