Car infotainment systems need multi-output power ICs: Page 7 of 9

March 11, 2013 //By Nathan Hanagami, Steve Knoth and Marty Merchant
Car infotainment systems need multi-output power ICs
Nathan Hanagami, Steve Knoth and Marty Merchant of Linear Technology examine why car infotainment systems need multi-output power ICs.
generation of radio frequency energy. It is necessary to use shielded inductors and to place those inductors as close to the LTC3375 as possible. This is because the AC currents circulate from the LTC3375 through the inductor and the output capacitor to ground and back to the LTC3375. From this it is also clear that wide traces, preferably area fill, be used to connect the ground of the output capacitors to the ground of the LTC3375 and to the ground of the associated V IN input decoupling capacitors as well.

The LTC3375 provides some additional tools for source suppression. The slew rate of the switch on the buck regulators can be adjusted, via I 2C. Since the buck regulators are synchronous, both the fall and the rise time are then increased. Figure 2 and Figure 3 show plots of switching with full speed and reduced speed (respectively) rise and fall times:

Figure 2: Buck regulator switching @2MHz with full speed rise & fall times
Click on image to enlarge


Figure 3
is a plot of switching with reduced speed rise and fall times:


Figure 3: Buck regulator switching @2MHz, reduced speed rise & fall times
Click on image to enlarge

Linear regulator controller

The linear controller may be run off of the 12V battery supply, supplying a relatively small amount of current. The output power of the LDO is dependent on the components used. It can be sized to provide 50mA @ 20V. This enables to supply power to any “Always On” circuitry in an automotive infotainment system, while the LTC3375 consumes 11uA of current in its powered down state. In this example, it eliminates the need for a separate low power supply to maintain the system memory. See Figure 4 for details.

Figure 4: Typical application circuit with Linear controller powering Vcc

Immunity to extreme voltage excursions

Another hurdle for automotive electronics is the dramatic changes in battery

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