2.3-W, stereo Class-D audio amp with 155-mW headphone amp & 3D enhancement

The LM49270 is a fully integrated audio subsystem designed for stereo multimedia applications. The LM49270 combines a 2.2W stereo Class D amplifier with a 155mW stereo headphone amplifier, volume control, headphone sense, and National’s unique 3D sound enhancement into a single device. The LM49270 uses flexible I 2C control interface for multiple application requirements.

The filterless stereo class D amplifiers delivers 2.2W/channel into a 4Ω load with less than 10% THD+N with a 5V supply. The headphone amplifier features National’s Output Capacitor-less (OCL) architecture that eliminates the output coupling capacitors required by traditional headphone amplifiers.

The IC features a headphone sense input (HPS) that automatically detects the presence of a headphone and configures the device accordingly. The LM49270 can automatically switch from OCL headphone output to a line driver output. If the VOC pin is pulled to GND, the VOC amplifier is disabled and the VOC pin is internally set to GND. This feature allows the LM49270 to be used as a line driver in OCL mode without a GND conflict on the headphone jack sleeve. Additionally, the headphone amplifier can be configured as capacitively coupled (CC).

The LM49270 features a 32 step volume control for the headphone and stereo outputs. The device mode select and volume are controlled through an I 2C compatible interface.

Output short circuit and thermal shutdown protection prevent the device from being damaged during fault conditions. Superior click and pop suppression eliminates audible transients on power-up/down and during shutdown. The LM49270 is available in a space saving 28-pin, 5x5mm LLP package.

Key Specifications ■  Stereo Class D Amplifier Efficiency:  VDD = 3.3V, 450mW/Ch into 8Ω 84%  VDD = 5V, 1W/Ch into 8Ω 84% ■  Quiescent Power Supply Current, VDD = 3.3V  Speaker Mode 5.5mA  Headphone Mode (OCL) 4mA ■  Power Output/Channel, VDD = 5V  Class D Speaker amplifier:  RL = 4Ω, THD+N = ≤ 10% 2.2W  RL = 8Ω, THD+N = ≤ 1% 1.06W  Headphone amplifier:  RL = 16Ω, THD+N = ≤ 1% 155mW  RL = 32Ω, THD+N = ≤ 1% 90mW ■  Shutdown current 0.02μA