Automotive power supply design that uses cold car to achieve seamless conversion

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Overview:
This article describes the automotive power solution that uses the LTC3115-1 buck-boost DC/DC converter to provide uninterrupted operation during load dump transients and even cold cranking. The flexibility and efficiency of this design is ideal for demanding next-generation automotive electronics and portable equipment.

Handheld devices, industrial instrumentation, and automotive electronics systems require power solutions that support multiple input voltages, which are generated by automotive input voltage transients, resistive circuit voltage drops, and multiple power supplies. A further design challenge is that applications often require a variety of stable voltage rails, including some voltage rails that are within the input voltage range. The LTC3115-1 buck-boost DC/DC converter features a wide range of 2.7V to 40V input and output voltage capabilities, high efficiency, small footprint, and seamless operation between boost and buck modes. The ability to convert is easy to meet the needs of such applications.

As far as automotive electronics systems are concerned, the LTC3115-1 can operate without interruption during load dump transients and even the harshest cold-start conditions. The device's programmable switching frequency optimizes efficiency and supports operation at 2MHz to ensure that switching noise and harmonics fall above the frequency of the AM broadcast band. The LTC3115-1 uses a proprietary low-noise PWM control algorithm that minimizes electromagnetic emissions in all operating conditions, even when switching between boost and buck modes of operation and over the entire load current range. An internal phase-locked loop allows the switch edges to be synchronized with an external clock for further control of EMI in noise-sensitive applications.

The accurate RUN pin is controlled by independent hysteresis and provides a programmable input undervoltage lockout threshold. The LTC3115-1 consumes only 30μA of quiescent current when operating in Burst Mode and 3μA in stop mode, thus reducing the standby leakage current of the car battery to a negligible level.

The LTC3115-1 is also ideal for handheld devices that require multiple power supplies. While it is common for portable devices to be powered by a dedicated AC adapter or a single power supply, many portable devices must now be compatible with a variety of inputs, including automotive, USB, Firewire, and unregulated AC adapters. A new generation of military radios and supporting electronic systems is an extreme example of the need to work with all available power sources for emergency use and to minimize the types of batteries that must be carried to the field.

In addition, in order to reduce the design burden, many product lines are designed with a single power supply, and multiple versions of the product share a design. This requires the most common power supply to support the input voltages that will be used by any product in the family. With a wide input and output voltage range of 2.7V to 40V, internal power switching, and high efficiency, the LTC3115-1 provides the functionality and flexibility required for these demanding applications.

figure 1:

Figure 1: 5V Regulator with 2.7V to 40V Wide Input Range

(Please read the PDF for details)