LT3689 Step-down regulator

Linear Technology has released the LT3689, a 700 mA, 36 V input step-down switching regulator with a power-on reset and watchdog timer.

Its Burst Mode operation keeps quiescent current under 85 µA in no load standby. The device’s 3.6 to 36 V input range, with 60 V transient ride through, makes it suitable for load dump and cold crank conditions commonly found in motor vehicle applications. Its 1.2 A internal switch can deliver up to 700 mA of continuous output at voltages as low as 0.8.

The Burst Mode operation provides ultra-low quiescent current for applications such as motor vehicle or telecom systems, which demand always-on operation and optimum battery life. Switching frequency is user programmable from 350 kHz to 2.2 MHz, enabling the designer to optimise efficiency while avoiding noise-sensitive frequency bands.

The integrated microprocessor supervisor functions support high reliability applications such as motor vehicle 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.

The device uses a high-efficiency 1.2 A, 450 mV 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 15 mV_PK-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 good loop stability. Other features include external synchronisation (from 350 kHz to 2.2 MHz), a power good flag and soft-start capability.