The TPA2000D4 is a 2-W stereo bridge-tied-load (BTL) class-D amplifier designed to drive speakers with as low as 4- impedance. The amplifier uses TI's second-generation modulation technique, which results in improved efficiency and SNR, and also allows the device to be connected directly to the speaker without the use of the LC output filter commonly associated with class-D amplifiers (this will result in an EMI which must be shielded at the system level). These features make the device ideal for use in notebook PCs where high-efficiency is needed to extend battery run-time. For speakers powered off the USB bus, the high-efficiency allows for higher output power levels without tripping the USB's overcurrent circuitry.