Regulator Powers Low-Voltage, High-Current Devices

Linear Technology offers the LT3071, a digitally programmable linear regulator with low dropout voltage, low noise and fast transient response for powering FPGAs and microprocessors, for example. The LT3071 is ideal for efficiently powering low-voltage, high-current devices such as DSPs, ASICs, sensitive communication supplies, server/storage devices, and post-buck regulation applications. Dropout voltage at 5A is an ultra-low 85mV.

Output voltage noise at 5A is 25uVRMS over a 10Hz to 100kHz bandwidth. The LT3071's 1MHz unity bandwidth, coupled with its minimum 15uF ceramic output capacitance, provides 30mV of overshoot/undershoot in response to a fast 4.5A output load step, saving bulk capacitance, space and cost. Its output voltage is digitally programmable from 0.8V to 1.8V in 50mV increments. Accuracy is tightly specified at +/- 1 per cent over line, load and temperature. An analogue output margining feature can adjust system output voltage over a continuous +/- 10 per cent range, advantageous during system debug.

A 'power-good' flag indicates if output voltage is in regulation or if the device is in UVLO, and the flag also provides an early warning indication of a thermal fault. An output current monitor sources a scaled dynamic representation of output current (IOUT/2500) that can be measured directly or terminated with a resistor and converted to voltage, allowing load conditions or power to be calculated. The LT3071's input supply voltage range is 0.95V to 3.0V and its bias supply voltage ranges from 2.2V to 3.6V.

The bias supply provides gate drive to the internal NMOS pass device. Multiple LT3071 devices can be easily paralleled for higher output current and to spread heat across a circuit board. A tracking feature can control a buck regulator powering the LT3071's input. This tracking function drives the upstream buck regulator to maintain the LT3071's input voltage at VOUT +300mV, minimising power dissipation.

If output voltage is dynamically changed, the tracking function automatically adjusts the output voltage of the buck regulator to maintain efficiency. Internal protection circuitry includes UVLO, reverse-current protection, precision current limiting with power foldback and thermal shutdown with hysteresis. The LT3071 is offered in a thermally enhanced, low-profile (0.75mm) 28-lead 4 x 5mm QFN package, and both E and I grades operate from -40C to +125C junction temperature range.

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