Data Sheet AS3501 AS3502 Low Power Ambient Noise-Cancelling Speaker Driver Line Input 1 General Description volume control via serial interface or volume pin The AS3501/02 are speaker driver with Ambient Noise 64 steps 0.75dB and MUTE, pop-free gain setting Cancelling function for headsets, headphones or ear single ended stereo or mono differential mode pieces. It is intended to improve quality of e.g. music lis- tening, a phone conversation etc. by reducing back- ANC processing ground ambient noise. feed-forward cancellation The fully analog implementation allows the lowest power consumption, lowest system BOM cost and most natural feed-back cancellation with filter loop transfer func- received voice enhancement otherwise difficult to tion definable via simple RC components achieve with DSP implementations. The device is simple in production SW calibration designed to be easily applied to existing architectures. 12-30dB noise reduction (headset dependent) An internal OTP-ROM can be optionally used to store the microphones gain calibration settings. 10-2000Hz wide frequency active noise attenuation (headset dependent) The AS3501/02 can be used in different configurations for best trade-off of noise cancellation, required filtering Monitor Function functions and mechanical designs. for assisted hearing, i.e. to monitor announcements The simpler feed-forward topology is used to effectively fixed (OTP prog.) ambient sound amplification to reduce low frequency background noise. The feed-back compensate headphone passive attenuation topology with either 1 or 2 filtering stages can be used to reduce noise for a larger frequency range, and to even volume controlled ambient sound amplification implement transfer functions like speaker equalization, mixed with fixed (OTP prog.) attenuation of LineIn Baxandall equalization, high/low shelving filter and to set a predefined loop bandwidth. Incremental Functions The filter loop is optimized by the user for specific head- ANC with or without music on the receiving path set electrical and mechanical designs by dimensioning improved dynamic range playback simple R, C components. simple and low cost single noise detection micro- Most headset implementations will make use of a single phone implementation noise detecting microphone. Two microphones could be used to allow for increased flexibility of their location in OTP ROM for automatic trimming during production the headset mechanical design. Using the bridged mode allows to even drive high impedance headsets. Performance Parameter 5/3.8mA 1.5V stereo/mono ANC <1uA quiescent extended PSRR for 217Hz 2 Key Features Interfaces Microphone Input 2 wire serial control mode & volume inputs 128 gain steps 0.375dB and MUTE with AGC calibration via Line-In or 2-wire serial interface differential, low noise microphone amplifier single cell or fixed 1.0-1.8V supply with internal CP single ended or differential mode Package supply for electret microphone AS3501 QFN24 4x4mm 0.5mm pitch MIC gain OTP programmable AS3502 QFN32 5.x5mm 0.5mm pitch High Efficiency Headphone Amplifier 2x34mW, 0.1% THD 16, 1.5V supply, 100dB SNR 3 Applications bridged mode for e.g. 300 loads Ear pieces, Headsets, Hands-Free Kits, Mobile Phones, click and pop less start-up and mode switching Voice Communicating Devices www.austriamicrosystems.com Revision 1.13 1 - 45AS3501 AS3502 1v2 Data Sheet Figure 1. AS3501 Feed Forward ANC Block Diagram Figure 2. AS3502 Feed-Back Block Diagram www.austriamicrosystems.com Revision 1.13 2 - 45