Clever converters help purchasers address growing demand for dual voltage power in automotive systems, without ramping up the component count, explains Digi-Key Electronics’ Rich Miro.
The LV148 automotive standard combines the existing automotive 12V system with a secondary 48V bus. The 12V bus will typically continue to provide power to systems such as lighting, infotainment, audio, and ignition while the 48V bus will supply systems like the adjustable suspensions, electric turbos/superchargers, air conditioning compressors, and active chassis along with regenerative braking support.
Implementing this additional 48V supply network will present various challenges. To help alleviate these issues, Linear Technology offers several DC/DC converters that handle bi-directional energy transfer very efficiently. With these converters, either battery could be charged and current could be supplied to the same load when needed.
Unlike many early 12V/48V dual battery DC/DC converter designs that utilize separate power components to step-up and step-down the voltage, Linear Technology’s LTC3871 bi-directional DC/DC controller uses the same external power components for stepping down the voltage as it does for stepping it up.
An integrated solution
The LTC3871 is a bi-directional 100V/30V two phase synchronous boost or buck controller. It can provide bi-directional DC/DC control and battery charging between the 12V and 48V system networks. It operates in boost mode from the 12V bus to the 48V bus and in buck mode from the 48V bus to the 12V bus.
This device allows both batteries to simultaneously supply energy when additional power is required. The maximum current delivered to the load is regulated by the on-chip current programming loop. There are four control loops that enable the control of voltage and current on either of the 12V or 48V busses.
To provide more output current without increasing input or output voltage ripple, users can daisy chain multiple LTC3871s and run them out-of-phase. A maximum of twelve phases can be daisy chained to run simultaneously out-of-phase with respect to each other.
The demonstration board for the LTC3871 can be configured in either two or four phases with one or two LTC3871s.
Efficiency curves for the devices are encouraging. Looking at a four-phase demonstration board utilizing two LTC3871 devices, the buck mode curve shows the efficiency as the board steps a 48V input down to 12V at up to 60A, while the boost mode curve shows the efficiency as the board steps a 12V input up to 48V and up to 10A. On both curves, peak efficiencies are around 97 per cent.
Not only will the LTC3871 bring a new level of performance and enhanced control, it also has the power to simplify dual battery 48V/12V DC/DC automotive systems. By allowing the same external power components to be used for both step-up and step-down purposes, this clever converter could well cut your component count.