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Switching Regulator Stays Stable During Input Transitions

04 October 2016

LTC3126 from Linear Technology synchronous step-down switching regulator. Source: Linear TechnologyLTC3126 from Linear Technology synchronous step-down switching regulator. Source: Linear TechnologyThe LTC3126 from Linear Technology is a 2.5 A, 42 V synchronous step-down switching regulator with an integrated dual input PowerPath™ control. The regulator’s power stage topology enables operation from either of two independent power sources, with seamless, internally controlled transitions between inputs to ensure a stable output voltage during hot-plug and power source disconnect events. Internal power switches and synchronous rectification combine to deliver 95% efficiency over a wide voltage range, enable a fast transient response, and ensure loop stability while switching at 2 MHz. This allows designers to avoid critical noise-sensitive frequency bands such as AM radio, while providing a highly compact solution footprint.

The LTC3126’s current mode topology is internally compensated, eliminating the need for external compensation components. Burst Mode® operation maintains high efficiency at low output currents while keeping peak-to-peak output ripple below 1%. Further, it features a quiescent current under 2 µA in no-load standby conditions, ideal for always-on systems and portable applications.

The LTC3126’s wide 2.4 V to 42 V input and 0.818 V to VIN output voltage ranges are suited for automotive applications which must regulate through cold-crank, load dump and stop-start scenarios. Integrated lossless PowerPath circuitry supports seamless operation from two separate input power sources. Pin-selectable ideal diode-OR and priority input modes with user-programmable undervoltage lockout thresholds provide full control over the transition between the input power sources.

The fast, automatic switchover provided by this internal PowerPath eliminates the need for hold-up capacitors and minimizes disturbances on the output rail. An active input channel indicator and independent input and output power good signals provide complete feedback of the power system status. Other features include 1 µA current in shutdown, internal soft-start and thermal protection.

The LTC3126 is housed in thermally enhanced 28-lead TSSOP and 4 mm x 5 mm QFN packages. These packages, when combined with the device’s high switching frequency that enables small external inductors and capacitors, provide a compact, thermally efficient footprint. E-and I-grade devices both feature an operating junction temperature of –40 °C to 125 °C. The H-grade high reliability version is offered in TSSOP only and is tested and guaranteed to operate from –40 °C to 150 °C operating junction temperature. Pricing starts at $6.25 each in 1000-piece quantities. All versions are available from stock.

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