36VIN, 4A (IOUT), 1.5MHz Synchronous Step-Down DC/DC Converter

18 FEBRUARY 2011

Linear Technology Corporation announces the LT3690, a 36V input capable, synchronous step-down switching regulator which can deliver up to 4A of continuous output current at efficiencies as high as 93%. The LT3690 operates within a VIN range of 3.9V to 36V, and offers transient protection to 60V, making it well suited for load dump and cold-crank conditions found in automotive applications. The LT3690’s Burst Mode® operation requires only 70uA of quiescent current, ideal for applications such as automotive or telecom systems, which demand always-on operation and optimum battery life. Switching frequency is user-programmable from 170kHz to 1.5MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. The combination of its 4mm x 6mm QFN-26 package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.
The LT3690 utilizes a high efficiency 5.5A, 90mOhm high-side switch with the necessary boost diode, oscillator, control and logic circuitry integrated into a single chip. The 30mOhm internal synchronous power switch increases efficiency and eliminates the need for an external Schottky catch diode. Low ripple Burst Mode operation maintains high efficiency at low output current while keeping output ripple below 15m VPK-PK. Special design techniques enable high efficiency over a wide input voltage range and the device’s current mode topology enables fast transient response and excellent loop stability. Other features include external synchronization (from 170kHz to 1.5MHz), a power good flag and robust short-circuit protection.
The LT3690EUFE is priced at $4.95 each for 1,000-piece quantities. The LT3690IUFE is tested and guaranteed to operate from a -40 C to 125 C operating junction temperature and is priced at $5.45 each in 1,000-piece quantities. All versions are available from stock. For more information, visit www.linear.com/3690.

Summary of Features: LT3690
• Wide Input Range: Operation from 3.9V to 36V, Overvoltage Lockout Protects Circuits Through 60V Transients
• 4A Maximum Output Current
• Integrated 30mOhm N-Channel Synchronous Switch
• 70µA IQ at 12VIN to 3.3VOUT
• Low Ripple Burst Mode® Operation Allows Output Ripple < 15mVP-P • Programmable Input Undervoltage Lockout • 0.8V Feedback Reference Voltage • Output Voltage 0.8V to 20V • Programmable & Synchronizable Oscillator (170kHz to 1.5MHz) • Soft-Startup & Output Voltage Tracking • Short-Circuit Robust • Power Good Flag • Small Thermally Enhanced 4mm x 6mm QFN Package

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