Dual output synchronous step-down DC/DC controller offers highly balanced current sharing

March 09, 2011 // By Christoph Hammerschmidt
For applications with noise sensitive requirements, Linear Technology has developed the LTC3869/-2, a dual output synchronous step-down DC/DC controller with an efficiency of up to 95 percent. The device features highly balanced current sharing between channels when paralleled, the vendor promises.

For applications with noise sensitive requirements, Linear Technology has developed the LTC3869/-2, a dual output synchronous step-down DC/DC controller with an efficiency of up to 95 percent. The device features highly balanced current sharing between channels when paralleled, the vendor promises.

According to Linear Technology, the controller can maintain better than ±4% current mismatch between channels during steady state and transient conditions when both outputs are paralleled due to its low 2 mV sense voltage maximum mismatch. The device's 4 V to 38 V input range encompasses a wide variety of applications, including most intermediate bus voltages and battery chemistries. The 1.1-Ohm onboard gate drivers minimize switching losses and allow the use of high power external MOSFETs to produce output currents up to 25 A per channel with output voltages ranging from 0.6 V to 12.5 V. Its performance is highly jitter-free even when the switching edges cross between phases, which makes the LTC3869/-2 a good choice for noise sensitive requirements. Applications include ASIC and FPGA supplies, power distribution, network servers and automotive power systems.

The LTC3869/-2's current-mode control and minimum on-time of just 90 ns recommend the chip also for high frequency, high step-down ratio applications requiring a small solution size. Tracking and sequencing functions optimize power-up and power-down of multiple power rails. This device operates with all N-channel MOSFETs and produces ±1% accurate output voltages over a wide -40 °C to 125 °C operating junction temperature range. The output current is sensed by monitoring the voltage drop across the output inductor (DCR) for highest efficiency or by using a sense resistor. A fixed operating frequency can be programmed from 250 kHz to 780 kHz or can be synchronized to an external clock with its internal phase-locked loop (PLL). Additional features include an onboard LDO for IC power, programmable soft start, a power good signal and external VCC control.

The LTC3869 is pin compatible to the LTC3850 in both