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Linear Technology Releases New DC/DC Controller That Maintains Regulation During Engine Restarts
Voltage Regulation is Maintained Over a 2.2V to 60V Input Range
Linear Technology Corporation has released the LTC3899, a triple output (buck,
buck, boost) 29µA quiescent current, synchronous DC/DC controller that maintains output voltage regulation over a
2.2V to 60V input range. A 12V car 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 boost converter feeds
two stepdown converters, avoiding output voltage dropout when a car battery droops, a useful feature in automotive
start/stop systems that shut off the engine at idle to save fuel. The 60V maximum input voltage covers double battery
truck applications. Alternatively, the buck controllers can be powered from the input as a general purpose triple
The LTC3899 operates from an input voltage of 4.5V to 60V during startup and maintains operation down to 2.2V after startup.
The boost and buck converters can produce output voltages up to 60V with efficiencies as high as
95%. In applications where the input voltage may exceed the regulated output voltage, the LTC3899 keeps the
synchronous boost MOSFET on continuously so that the output voltage follows the input voltage with minimal power
In addition, the LTC3899 can be configured for Burst Mode® operation, reducing quiescent current to 29µA for one
channel (39µA for all three channels on) with outputs in regulation in standby mode, a useful feature for preserving
battery run times. The powerful 1ohm onboard all Nchannel gate drivers minimize MOSFET switching losses and
provide for output currents of more than 10 amps per channel, limited only by external components. Furthermore, the
output current for each converter can be sensed by monitoring the voltage drop across the inductor (DCR) or by
using a sense resistor. The LTC3899's constant frequency current mode architecture enables a fixed frequency from
50kHz to 900kHz or it can be synchronized to an external clock from 75kHz to 850kHz. Additional features include
an onboard LDO for IC power and gate drive, output voltage tracking or adjustable softstart, a power good signal
and an optional external V bias input.
The LTC3899 is available in 38lead SSOP and 38pin
5mm x 7mm QFN packages. Four temperature grades are available, with operation from 40°
to 125°C for the extended and industrial grades, a high temp automotive grade of 40°C to 150°C and
a military grade of 55°C to 150°C.
Key Features of the LTC3899
- All Outputs Remain in Regulation During Engine Restart
- Wide Input Voltage Range: 4.5V to 38V During StartUp, Down to 2.2V After StartUp
- Boost Output Voltage Up to 60V
- Buck Output Voltage Range: 0.8V to 60V
- Low 29µA Quiescent Current During Standby Condition
- Up to 95% Efficiency
- Powerful Onboard All N-Channel Gate Drivers
- Power Up/Down Tracking & Sequencing Current Mode Control
- Fixed Programmable Operating Frequency from 50kHz to 900kHz
- Synchronizable Operating Frequency from 75kHz to 850kHz
The company's Web site address is www.linear.com.
[Reprinted with kind permission from Linear Technology - Release Date: 27th January, 2015]