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January 2017
DocID029728 Rev 1
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AN4909
Application note
Intelligent power switches for 48 V battery applications
Nicolas Aupetit, Alberto Villegas
Introduction
For the last 15-20 years, the automotive electronics market has been moving from electromechanical
relays to solid state components for driving all kind of loads.
It is obvious why: solid state components are smaller in size, lighter, silent, easy to mass produce
because they are housed in SMD packages, and they boast an unrivaled number of switching
activations. On top of this, the solutions based on silicon components have a much higher electrical
efficiency and offer useful types of diagnostics such as short-circuit, overload and thermal protections,
they can supply an actual image of the current flowing into the load, and so on. In fact, they are called
“Intelligent Power Switches (IPS)” or “Smart Power MOSFETs” for good reasons. The key “switching”
element is an N-MOSFET, with the relevant charge pump. Around the N-MOSFET, logic interfaces and
other elements contribute to the protection of the MOS and they generate and manage diagnostic data.
There are two categories of IPS, depending on where the “switch” is placed. If the switch is placed
between the load and the ground of the circuit, it is called “low-side.” If the switch is placed between the
high voltage and the load (and this is connected directly to the ground), it is a “high-side” configuration.
The high-side configuration offers interesting advantages in automotive applications such as high
safety, reduction of battery leakage currents, as well as being a real-time (analog) load current mirror.
IPS are available for standard 12 V and 24 V batteries. In the not-too-distant future, high-end diesel and
gasoline cars may have two batteries on board: a main battery of “48 V” and a secondary battery of
“12 V.” The main interest of the 48 V battery is to support fuel economy and reduce pollutant emissions,
especially CO
2
. The use of a 48 V battery should help to increase a car's efficiency: for example, by
using thinner wires in the cars. Actually, if the battery voltage is higher, to drive the same power, the
current is lower. A 48 V battery is a good trade-off between safety and functionality.
Several new electronic systems powered by 48 V batteries are already available. More and more often
in the future, it will be necessary to have IPS to drive some loads currently driven by the 12 V Smart
Power MOSFETs.
Therefore, because of the maximum possible voltage (60 to 70 V) on 48 V batteries, and the spikes
generated inside the car, the MOSFET switches will have to withstand voltages in the order of 80 V at
25 °C.
Today the number of Smart Power MOSFETs or IPS able to comply with these requirements is
extremely low and they are expensive.
In this application note, we demonstrate a way to design circuits able to drive all kinds of loads with
components already in mass production, that are AEC-Q100 or AEC-Q101 qualified, and that offer
functionalities similar to those of the 12 V or 24 V IPS available in the market today.
