An 86% efficiency SIMO DC-DC converter with one boost, one buck, and a floating output voltage for car-radio

The design of Class-D audio power amplifiers [1] for car radio is challenging because of the large voltage variation of the automotive battery. During crank and dump, the 14.4V battery voltage may sharply (in less than 2ms) drop down to 4V or rise up to 40V. For a proper operation, the supply voltages of the Class-D amplifier must be properly controlled for all the battery conditions. The block diagram of the Class-D power amplifier in Fig. 27.3.1 helps in defining the set of required supply voltages. The power audio stage uses n (n =1,...,4) channels of high and low-side switches both made by n-type transistors. The choice optimizes the on-resistance and the gate capacitance to achieve the best efficiency, but requires a boosted voltage (V
_boost
) to drive the high-side devices. A regulated low voltage (V
_reg-low
=4.5V) supplies the driver of N
_pow-LS
. As the digital and analog processing are performed at V
_ba
/2 to improve the system SNR, the digital core uses a floating voltage (V
_floatH
-V
_floatL
=1.8V) across V
_bat
/2.