February 8, 2013 – Linear Technology Korea (CEO Hong Sa-gwak) announced the launch of a triple output (buck, buck, boost), low quiescent current synchronous DC/DC controller (product name: LTC3859AL). This product maintains all output voltages during regulation under automotive cold crank conditions. A 12V automotive battery can drop below 4V during engine restart or cold crank, which can cause resets in infotainment systems and other electronic equipment operating at 5V and above. The high-efficiency synchronous boost converter powers two step-down converters, preventing output voltage drop when automotive battery voltage decreases. This feature is useful in automotive start/stop systems that shut down the engine while stopped to reduce fuel consumption. Alternatively, the buck controller can receive power from the input for a general-purpose triple output controller.

The LTC3859AL operates at input voltages of 4.5V to 38V during startup and maintains operation at voltages as low as 2.5V after startup. The synchronous boost converter can generate output voltages up to 60V and operates at 0% duty cycle (synchronous switch ON) when maximum efficiency is needed, allowing input voltage to pass through directly. The two step-down converters can generate output voltages from 0.8V to 24V across the entire system with maximum efficiency of 95%. Additionally, the LTC3859AL can be configured for Burst Mode® operation, reducing quiescent current to 28µA per channel in standby mode. This feature is a useful method for preserving battery operating time.

The robust 1.1Ohm onboard gate driver minimizes all N-channel MOSFET switching losses, and while related to external component usage, can supply output currents exceeding 10A per channel. Additionally, the output current of each converter is sensed by monitoring the voltage DCR (drop across the inductor) or by using individual sense resistors. The LTC3859AL's fixed-frequency current mode architecture allows frequency selection between 50kHz and 900kHz, and can be synchronized with external clocks using an internal PLL (phase-locked loop) in the range of 75kHz to 850kHz.

Additional features include an integrated LDO for power supply within the IC and gate drive, output voltage tracking or adjustable soft start, power good signal, and external VCC input. Reference voltage accuracy is ±1% over the operating temperature range of -40°C to 125°C.

The LTC3859AL is supplied in 38-pin SSOP and 38-pin 5mm x 7mm QFN packages. Available in four temperature grades: operating from -40°C to 125°C for extended or industrial grade, -40°C to 150°C for automotive grade, and -55°C to 150°C for military grade. Starting at $4.76 per unit based on quantities of 1,000. Detailed information is available at www.linear.com/product/LTC3859AL.

Product Features: LTC3859AL
• Regulates all outputs during engine restart
• Wide input voltage range of 4.5V to 38V at startup, operation maintained down to 2.5V input after startup
• Boost output voltage up to 60V
• Buck output voltage range: 0.8V to 24V
• Low quiescent current of 38µA during standby
• Maximum efficiency of 95%
• Powerful onboard all N-channel gate driver
• RSENSE or DCR current sensing
• Output voltage up/down tracking & sequencing
• Programmable fixed operating frequency range: 50kHz to 900kHz
• PLL (Phase-Locked Loop) synchronization available at 75kHz to 850kHz
• ±1% VREF accuracy over operating temperature range of -40°C to 125°C
• Current mode control