Linear Technology LTC3859 DC/DC controller

Linear Technology has introduced the LTC3859, a triple output (buck, buck, boost), low quiescent current synchronous DC/DC controller that maintains all output voltages in regulation during motor vehicle cold crank conditions.

A 12 V car battery can droop to less than 4 V during engine restart or cold crank, causing reset of infotainment systems and other electronics that operate from 5 V and higher.

The synchronous boost converter feeds the two step-down converters, avoiding output voltage dropout when the car battery droops. Alternatively, the controllers can be powered from the input for a general-purpose triple output controller.

The device operates from an input voltage of 4.5 to 38 during start-up and maintains operation down to 2.5 V after start-up. The 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 maximise efficiency.

The two step-down converters can produce output voltages from 0.8 to 24 with the entire system achieving efficiency to 95%.

In addition, the controller can be configured for Burst Mode operation, which reduces quiescent current to less than 55 µA per channel (80 µA for all three on) in sleep mode. The 1.1 Ω onboard all N-channel gate drivers minimise MOSFET switching losses and allow an output current of more than 10 A per channel, only limited by external components.

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 device’s constant frequency current mode architecture allows for a selectable frequency from 50 to 900 kHz or it can be synchronised to an external clock with its internal phased-lock loop from 75 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 to 125°C operating temperature range.