What this part is and where it fits
The Texas Instruments LM49155TLX/NOPB is a stereo headphone amplifier from the Boomer® series that can operate in either Class D or Class AB mode. It is designed for portable and mobile audio applications where uplink noise suppression (E²S) and I²C-controlled volume are needed — think smartphone earpiece drivers, tablet audio paths, or any handset where the microphone return path must reject transmit-side noise. The part comes in a 36-ball DSBGA package for a compact footprint on a multi-layer PCB.
Key features and what they mean for the BOM
The dual-mode output stage (Class D vs Class AB) lets the designer trade efficiency against external filtering. Class D gives higher efficiency for battery-powered gear; Class AB avoids the LC filter on the output and keeps the BOM count lower. The I²C control bus handles volume, mode switching, and shutdown — no extra GPIOs needed. The E²S (Enhanced Earbud Squelch) feature is the part's main differentiator: it suppresses uplink noise picked up by the headset microphone during a call, which is the kind of spec that matters when the audio path goes through a baseband processor that does not have its own noise gate. Depop circuitry reduces the click-and-pop on power-up and shutdown, and the differential inputs reject common-mode noise from the audio source. The shutdown pin (also I²C-accessible) lets the system power down the amplifier when the headset is unplugged, saving standby current.
Package and mounting
The 36-DSBGA package requires a solder-mask-defined pad layout and a stencil with small apertures. This is a fine-pitch BGA — not a hand-solder part.