Step down charge pump provides regulated output with input current doubling

In applications where the input voltage exceeds twice the output voltage, a charge pump offers nearly twice the efficiency of an equivalent linear regulator, and provides a space saving, inductor-free alternative to switching dc/dc regulators. The LTC3255 produces a regulated output (2.4 to 12.5V adjustable) from a 4 to 48V input that is +60V/-52V tolerant. At no load, Burst Mode operation reduces V_IN quiescent current to 16µA, and 2:1 capacitive charge pumping extends output current capability to approximately twice the input current. The LTC3255 is well suited for a variety of applications such as industrial control, factory automation, sensors and supervisory control and data acquisition systems, housekeeping power supplies, as well as current boosting voltage regulators for 4 to 20mA current loops. The LTC3255 operates either as a general purpose step down charge pump with 2:1 or 1:1 conversion ratios, or it can operate as a current doubling shunt regulator. In normal mode, the conversion ratio is chosen based on V_IN, V_OUT, and load conditions, and switching between conversion modes is automatic. In shunt mode, the device is forced into 2:1 mode, enabling the LTC3255 to provide a regulated output voltage from a current source input with nearly two times the input current available at the load. For example, this feature enables a 4mA current loop to power a 7.4mA load continuously with a 3.3V regulated output voltage. The LTC3255 withstands reverse polarity input supplies down to -52V and output short circuit without damage. Safety features, including an output current limit and over temperature protection have been included to further enhance robustness.