28-uA IQ triple output, buck/buck/boost synchronous DC/DC controller maintains regulation in automotive start/stop systems
A 12 V automotive battery can droop to less than 4 volts during engine restart or cold crank, causing reset of infotainment systems and other electronics that operate from 5 volts and higher. The high efficiency synchronous boost converter feeds the two step-down converters, avoiding output voltage dropout when the car battery droops, a useful feature in automotive start/stop systems that shut off the engine at idle to save fuel. Alternatively, the buck controllers can be powered from the input for a general purpose triple output controller.
The LTC3859AL operates from an input voltage of 4.5 V to 38 V during start-up and maintains operation down to 2.5 V after start-up. The synchronous boost converter can produce output voltages up to 60 V and can run at 0% duty cycle (synchronous switch ON) to pass through the input voltage when required to maximize efficiency. The two step-down converters can produce output voltages from 0.8 V to 24 V with the entire system achieving efficiency as high as 95%. In addition, the LTC3859AL can be configured for Burst Mode operation, reducing quiescent current to 28 µA per channel (38 µA for all three on) in sleep mode, a useful feature for preserving battery run-times.
The 1.1 Ohm onboard all N-channel gate drivers minimize MOSFET switching losses and provide an output current of more than 10 amps per channel, limited only by external components. Furthermore, the output current for each converter is sensed by monitoring the voltage drop across the inductor (DCR) or by using a separate sense resistor.
The LTC3859AL’s constant frequency current mode architecture enables a selectable frequency from 50 kHz to 900 kHz or it can be synchronized to an external clock with its internal phase-locked loop (PLL) from 75 kHz to 850 kHz.
Additional features include an onboard LDO for IC power and gate drive, output voltage tracking or adjustable soft start, a power good signal and an external VCC input. The reference voltage accuracy is ±1% over a -40°C to 125°C operating temperature range.
Availability and Pricing
The LTC3859AL is available in 38-lead SSOP and 38-pin 5 mm x 7 mm QFN packages. Four temperature grades are available, with operation from -40°C to 125°C for the extended and industrial grades, a high temp automotive range of -40°C to 150°C and a military grade of -55°C to 150°C. The 1,000-piece price starts at $4.76.
More information about the LTC3859AL DC/DC controller at
www.linear.com/product/LTC3859AL
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
