Features
| • | 24–Bit Stereo DAC |
| • | Stereo Filterless Class D Operation |
| • | Selectable spread spectrum mode reduces EMI |
| • | Ground Referenced Headphone Amplifiers with 100dB SNR |
| • | I
2S Compatible Audio Interface
|
| • | Audio Sample Rates up to 192kHz |
| • | National’s 3D Enhancement |
| • | 32-step Digital Volume Control |
| • | I
2C Compatible Control Interface
|
| • | Headphone Sense Input |
| • | Stereo Analog Line Inputs |
| • | Output Short Circuit Protection |
| • | Thermal Overload Protection |
| • | Minimum external components |
| • | Click and Pop suppression |
| • | Micro-power shutdown |
| • | Available in space-saving 32 pin LLP package |
Description The LM49450 is a fully integrated audio subsystem designed for portable media player applications. The LM49450 combines a
24-bit I
2S digital-to-analog converter (DAC), 2.5W/channel stereo Class D speaker drivers, 36mW stereo ground referenced headphone
drivers, volume control, and National’s unique 3D sound enhancement into a single device.
The filterless Class D amplifiers deliver 1.25W/channel into an 8Ω load with <1% THD+N with a 5V supply. The LM49450 offers
two logic selectable modulation schemes, fixed frequency mode, and an EMI reducing spread spectrum mode. The 36mW/channel
headphone drivers feature National’s ground referenced architecture that creates a ground-referenced output from a single
supply, eliminating the need for bulky and expensive DC-blocking capacitors, saving space and minimizing system cost. A headphone
sense input (HPS) automatically detects the presence of a headphone, and configures the device accordingly.
The LM49450 stereo, 24-bit DAC supports a wide range of sample rates (including 192kHz, 96kHz, 48kHz, and 44.1kHz). The digital
audio signal path features better than 100dB SNR, and low 0.05% THD+N when measured at the headphone outputs. The flexible
3-wire I
2S interface supports left or right justified audio data.
The LM49450 features separate 32-step volume control for the headphones and speaker outputs. 3D enhancement, mode selection,
shutdown control, and volume are controlled through an I
2C compatible interface.
Output short circuit and thermal overload 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 LM49450 is available in
a space saving 32-pin LLP package.
Key Specification
| ■
SNR at Headphone Output
|
102dBA (typ)
|
| ■
Speaker Amplifier Efficiency
at 3.6V, 650mW/channel into 8Ω
|
87% (typ)
|
| ■
Speaker Amplifier Efficiency
at 5V, 1.1W/channel into 8Ω
|
80% (typ)
|
| ■
Quiescent Power Supply Current
Line Inputs:
|
|
| Speaker Mode at LSVDD = 3.6V
|
7.5mA (typ)
|
| Headphone Mode at HPVDD = 2.5V
|
5.3mA (typ)
|
| ■
Output Power/Channel
|
|
| Speaker at LSVDD = 5V:
|
|
| RL = 4Ω, THD+N
≤ 10%
|
2.5W (typ)
|
| RL = 8Ω, THD+N
≤ 1%
|
1.25W (typ)
|
| Headphone at HPVDD = 2.5V:
|
|
| RL = 16Ω, THD+N
≤ 1%
|
34mW (typ)
|
| RL = 32Ω, THD+N
≤ 1%
|
36mW (typ)
|
| ■
PSRR at 1kHz
Speaker Mode
Headphone Mode
|
67dB ( typ)
77dB (typ)
|
| ■
Shutdown current
|
0.02μA (typ)
|
Applications
| • | Portable Media Players |
| • | Portable Navigation Devices |
| • | Multi-Media Monitors |
| • | Laptops |
| • | Portable Gaming Devices |
| • | Mobile Handsets |
|
|
LM49450
