Quad 1A step-down switching regulator with 100% duty cycle operation

July 09, 2012 // By Christoph Hammerschmidt
Linear Technology Corporation has announced the LT3504, a quad 1 A output, 40 V step-down switching regulator with 100% duty cycle operation. The LT3504's 3.2 V to 40 V input voltage range makes it ideal for automotive and industrial applications that require multiple outputs.

Its internal 1.5 A switches can deliver up to 1 A of continuous output current per channel to voltages as low as 0.8 V. The LT3504's unique design includes an onboard boost regulator, enabling each channel to operate at 100% duty cycle, even with input voltage as low as 3.2 V. This architecture makes the LT3504 well suited for applications requiring continuous output regulation, such as automotive cold-crank and stop-start scenarios. 

Switching frequency is user-programmable from 250 kHz to 2.2 MHz and synchronizable throughout the range, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands. The combination of its 28-lead 4-mm x 5-mm QFN and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint for multiple output applications.

The LT3504 utilizes four internal 1.5 A switches for the step-down conversion and a 220 mA switch for the internal boost circuit, with the necessary oscillator, control and logic circuitry integrated into a single die. Special design techniques and a new high voltage process deliver efficiencies up to 88% over a wide input voltage range, while the LT3504's current mode topology enables fast transient response and excellent loop stability. Anti-phase switching reduces input ripple and robust short-circuit protection enhances system reliability. Other features include output voltage tracking, programmable undervoltage lockout and a power good pin to indicate when all outputs are in regulation.

The LT3504EUFD is packaged in a 4-mm x 5-mm QFN-28, priced starting at $3.50 each for 1,000-piece quantities. The LT3504IUFD is tested and guaranteed to operate from a -40°C to 125°C operating junction temperature and is priced at $3.85 each in 1,000-piece quantities. Both versions are available from stock. 

www.linear.com/product/LT3504