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LT3689 - Micropower Step-Down Regulator Has On-Chip Power-On Reset & Watchdog Timer

6th May 2010

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Datasheet

Linear Technology has announced the LT3689, a 700mA, 36V input step-down switching regulator with a power-on reset and watchdog timer. Its Burst Mode operation keeps quiescent current under 85uA in no load standby conditions. The LT3689’s 3.6V to 36V input voltage range, with 60V transient ride through, makes it ideal 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 ultralow 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 optimize 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.

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% 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 utilizes 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 15mVPK-PK. 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 synchronization (from 350kHz to 2.2MHz), a power good flag and soft-start capability.