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Switching regulator cuts quiescent current

Posted: 02 Sep 2009     Print Version  Bookmark and Share

Keywords:switching regulator  watchdog timer  microprocessor 

Linear Technology Corp. debuted a new 700mA, 36V input step-down switching regulator with a power-on reset and watchdog timer.

The LT3689 features burst mode operation that keeps quiescent current under 85µA in no load standby conditions. The LT3689's 3.6V to 36V input voltage range, with 60V transient ride through, suits it for load dump and cold crank conditions commonly found in automotive applications. Its 1.2A internal switch can deliver up to 700mA of continuous output current at voltages as low as 0.8V.

The LT3689's burst mode operation provides ultra low quiescent current, well-suited for applications such as automotive or telecom systems, which demand always-on operation and optimum battery life. Switching frequency is user programmable from 350kHz to 2.2MHz, enabling the designer to optimise efficiency while avoiding critical noise-sensitive frequency bands. The LT3689's 3mm x 3mm QFN-14 (or thermally enhanced MSOP-16) package and high switching frequency keeps external inductors and capacitors small, providing a very compact, thermally efficient footprint.

In addition, the integrated microprocessor supervisor functions support high-reliability applications such as automotive electronic control units. 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 open collector RST will pull down if output voltage drops 10 per cent below the programmed value. The watchdog timer is pin-selectable for window or timeout modes. In timeout mode, WDO pulls low if too long a period passes before a watchdog transition is detected. In window mode, the LT3689 monitors for WDI falling edges grouped too close together or too far apart.

The LT3689 utilises a high efficiency 1.2A, 450mV switch, with an integrated boost diode, oscillator, control and logic circuitry integrated into a single die. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple below 15mVPKpPK Special design techniques and a new high voltage process enable high efficiency over a wide input voltage range, and current mode topology enables fast transient response and excellent loop stability. Other features include external synchronisation from 350kHz to 2.2MHz, a power good flag and soft-start capability.

The LT3689EUD and LT3689EMSE are priced starting at Rs.156.31 and Rs.158.76 ($3.20 and $3.25) each, respectively, for 1,000 piece quantities. The LT3689IUD and LT3689IMSE are tested and guaranteed to operate from a -40°C to 125°C operating junction temperature and are priced at Rs.173.90 and Rs.176.34 ($3.56 and $3.61) each, respectively, in 1,000 piece quantities. Finally, the LT3689HMSE is tested and guaranteed to operate from a -40°C to 150°C operating junction temperature and is priced at $3.86 each in 1,000 piece quantities. All versions are available from stock.

Get related application notes and technical articles on Power Design India.

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