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Uplink Noise Suppression & Downlink SNR Enhancement Analog Audio Subsystem
The LM49155 is a fully integrated audio subsystem designed for portable handheld applicaTIons such as cellular phones. The LM49155 combines a Noise Suppression microphone amplifier, a 1.35W mono class D amplifier with ALC, class AB earpiece driver with AGC, a high efficiency, stereo, ground referenced headphone amplifier with click pop suppression and I2C modes select and volume control.
The LM49155 features analog fully differenTIal input, and differenTIal output microphone amplifier designed to reduce background acousTIc noise, while delivering superb speech clarity in voice communication applications. Downlink SNR enhancement with an advanced acoustic AGC technology to adjust output levels.
The LM49155 speaker amplifier features National's unique output limiter that provides both a no-clip feature and speaker protection. The E2S class D amplifier features a patented, ultra low EMI PWM architecture that significantly reduces RF emissions while preserving audio quality and efficiency. The headphone drivers feature National's ground referenced architecture that creates a ground-referenced output from a single, low-voltage supply.
The LM49155 is available in an ultra-small 36-bump micro SMD package (3.434mm x 3.459mm x 0.6mm).
LM49155 main indicators:
â– Uplink Far Field Noise Suppression Electrical FFNSE at f = 1kHz 34dB (typ)
â– Downlink SNR Enhancement Earpiece Amplifier
Near-Field SNR Enhancement 6 to 18dB (typ)
Downlink SNRIE 16dB (typ)
■Class D Loudspeaker Amplifier RL = 15μH + 8Ω + 15μH
POUT, THD + N ≤%, VDD = 5.0V 1.35W (typ)
■Headphone Amplifier RL = 32Ω
POUT, THD + N ≤%, HPVDD = 1.8V 19mW (typ)
LM49155 main features:
â– Noise cancellation for uplink and downlink without DSPtype artifacts, distortions or delays
â– Adapting AGC on ambient noise level & downlink signal strength for earpiece
â– Downlink adjustable noise-reducing high pass filter
â– E2S Class D Amplifier with ALC
â– Ground Referenced Headphone Outputs with Advanced Click Pop Suppression
â– Micro-power shutdown
LM49155 application:
â– Mobile Phones
â– Portable Electronic Devices 
figure 1. LM49155 simplified block diagram 
figure 2. LM49155 typical application block diagram
PowerWise noise reduction frequency power amplification technology designed by LM49155
This article introduces the main indicators of LM49155, simplified block diagram and typical application circuit. LM49155 is a highly integrated PowerWise audio subsystem of NS company, integrated noise suppression microphone amplifier, 1.35W mono class A amplifier with ALC, class AB headphone driver with AGC, high efficiency stereo reference Headphone amplifier and I2C mode selection and volume control. Mainly used in mobile phones and portable electronic devices.