Buck-boost DC/DC converter regulates through cold-crank and load-dump transients

June 20, 2013 // By John Canfield, Linear Technology Corp.
Handheld devices, industrial instruments and automotive electronics all demand power supply solutions that can support an expansive range of input voltages resulting from automotive input voltage transients, resistive line drops and a wide variety of power sources. As a further design challenge, applications often require a variety of regulated voltage rails, including some that fall within the input voltage range. The LTC3115-1 buck-boost DC/DC converter, with its wide 2.7V to 40V input and output voltage capability, high efficiency, small footprint and seamless transition between step-up and step-down modes of operation, easily meets the requirements of such applications.

For automotive electronics, the LTC3115-1 provides uninterrupted operation through load dump transients and even the harshest cold-crank conditions. Its programmable switching frequency optimizes efficiency and supports operation at 2MHz to ensure that switching noise and harmonics are located above the AM broadcast band. The LTC3115-1 employs a proprietary low noise PWM control algorithm that minimizes electromagnetic emissions over all operating conditions even during transitions between the step-up and step-down modes of operation and over the full range of load current. An internal phase-locked loop allows switching edges to be synchronized with an external clock for further control of EMI in noise-sensitive applications.

Figure 1. 5V regulator with wide 2.7V to 40V input range

An accurate RUN pin provides a programmable input undervoltage lockout threshold with independent control of hysteresis. By consuming only 30µA of quiescent current in Burst Mode operation and 3µA in shutdown, the LTC3115-1 reduces standby current drain on automobile batteries to negligible levels.

The LTC3115-1 is also well suited for handheld devices, which are required to interface to an expanding array of power sources. While it was once common for portable devices to be powered by a dedicated AC adapter or a single power source, many must now be compatible with a variety of inputs including automotive, USB, Firewire and unregulated wall adapters. Next generation military radios and support electronics are an extreme example, requiring the capability to operate from all available power sources for emergency use and to minimize the number of battery varieties carried in the field.

Additionally, in an effort to reduce design overhead, many product families utilize a single power supply design that is shared across multiple versions of a product. This requires that the common power supply support the widest range of possible input voltages that will be seen by any device within the family. With its wide 2.7V to 40V input and output voltage ranges, internal power switches and high efficiency

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