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PDF AS3500 Data sheet ( Hoja de datos )
| Número de pieza | AS3500 | |
| Descripción | Low Power Ambient Noise-Cancelling Speaker Driver | |
| Fabricantes | austriamicrosystems AG | |
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AS3500 AS3501 AS3502
Data Sheet, Confidential
Low Power Ambient Noise-Cancelling Speaker Driver
1 General Description
The AS3500/01/02 are speaker driver with Ambient
Noise Cancelling function for handsets, headphones or
ear pieces. It is intended to improve quality of e.g. music
listening, a phone conversation etc. by reducing back-
ground ambient noise.
The fully analog implementation allows the lowest power
consumption, lowest system BOM cost and most natural
received voice enhancement otherwise difficult to
achieve with DSP implementations. The device is
designed to be easily applied to existing architectures.
An internal OTP-ROM can be optionally used to store
the microphones gain calibration settings.
The AS3500/01/02 can be used in different configura-
tions for best trade-off of noise cancellation, required fil-
tering functions and mechanical designs.
The simpler feed-forward topology is used to effectively
reduce low frequency background noise. The feed-back
topology with either 1 or 2 filtering stages can be used to
reduce noise for a larger frequency range, and to even
implement transfer functions like speaker equalization,
Baxandall equalization, high/low shelving filter and to set
a predefined loop bandwidth.
The filter loop is optimized by the user for specific hand-
set electrical and mechanical designs by dimensioning
simple R, C components.
Most handset implementations will make use of a single
noise detecting microphone. Two microphones could be
used to allow for increased flexibility of their location in
the handset mechanical design. Using the bridged mode
allows to even drive high impedance headsets.
2 Key Features
Microphone Input
128 gain steps @0.375dB and MUTE with AGC
differential, low noise microphone amplifier
single ended or differential mode
supply for electret microphone
MIC gain OTP programmable
High Efficiency Headphone Amplifier
2x34mW, 0.1% THD @ 16Ω, 1.5V supply,
100dB SNR
bridged mode for e.g. 300Ω loads
click and pop less start-up and mode switching
Line Input
volume control via serial interface or volume pin
64 steps @ 0.75dB and MUTE, pop-free gain setting
single ended stereo or mono differential mode
ANC processing
feed-forward cancellation
feed-back cancellation with filter loop transfer func-
tion definable via simple RC components
simple in production SW calibration
12-30dB noise reduction (headset dependent)
10-2000Hz wide frequency active noise attenuation
(headset dependent)
Monitor Function
for assisted hearing, i.e. to monitor announcements
fixed (OTP prog.) ambient sound amplification to
compensate headphone passive attenuation
volume controlled ambient sound amplification
mixed with fixed (OTP prog.) attenuation of LineIn
Incremental Functions
ANC with or without music on the receiving path
improved dynamic range playback
simple and low cost single noise detection micro-
phone implementation
OTP ROM for automatic trimming during production
Performance Parameter
5/3.8mA @ 1.5V stereo/mono ANC; <1uA quiescent
extended PSRR for 217Hz
Interfaces
2 wire serial control mode & volume inputs
calibration via Line-In or 2-wire serial interface
single cell or fixed 1.0-1.8V supply with internal CP
Package
AS3500, AS3501 QFN24 [4x4] 0.5mm pitch
AS3502 QFN32 [5.x5] 0.5mm pitch
3 Applications
Ear pieces, Headsets, Hands-Free Kits, Mobile Phones,
Voice Communicating Devices
www.austriamicrosystems.com
Revision 1.00
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1 page  
AS3500 AS3501 AS3502 1v2
Data Sheet, Confidential - Pinout
4 Pinout
4.1 Pin Assignment
Please observe that pin assignment may change in preliminary data sheets.
Figure 3. Pin Assignments (Top View)
www.austriamicrosystems.com
Revision 1.00
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5 Page 
AS3500 AS3501 AS3502 1v2
Data Sheet, Confidential - Detailed Description
8.2 Microphone Input
8.2.1 General
The AFE offers two microphone inputs and one low noise microphone voltage supply (microphone bias). The inputs
can be switched to single ended or differential mode.
8.2.2 Gain Stage & Limiter
The Mic GainStage has programmable Gain within -6dB…+41.625dB in 128 steps of 0.375dB.
As soft-start function is implemented for an automatic gain ramping implemented with steps of 4ms to fade in the audio
at the end of the start-up sequence.
A limiter automatically attenuates high input signals. The AGC has 127 steps with 0.375dB with a dynamic range of the
full gain stage.
In monitor mode the gain stage can be set to an fixed (normally higher) gain level or be controlled by the VOL pin.
8.2.3 Supply
The MICS charge pump is providing a proper microphone supply voltage for the AAA supply. Since AAA batteries are
operating down to 1.0V, the direct battery voltage cannot be used for mic-supply. There are 2 modes.
The first mode SWITCH-MODE for 1.8V supply is to have just a switch from VBAT to MICS. With this switch, the micro-
phone current is switched off in idle mode.
The second mode CHAREGPUMP_MODE for AAA batteries is the real charge pump mode, in this mode a positive
voltage is generated of about 2* VBAT.
It is also possible to switch off the microphone supply if not needed (e.g. playback without ANC)
8.2.4 Parameter
VBAT=1.5V, TA= 25oC unless otherwise mentioned
Table 6. Microphone Input Parameter
Symbol
VMICIN0
VMICIN1
VMICIN2
RMICIN
Parameter
Input Signal Level
Input Impedance
Condition
AMIC = 30dB
AMIC = 36dB
AMIC = 42dB
MICP to AGND
ΔMICIN Input Impedance Tolerance
CMICIN
AMIC
Input Capacitance
Programmable Gain
Gain Steps
Gain Step Precision
discrete logarithmic gain steps
ΔAMIC
Gain Ramp Rate
Tinit=64ms
VATTACK
VDECAY
AMICLIMIT
Limiter Activation Level
Limiter Release Level
Limiter Gain Overdrive
VPEAK related to VBAT or VNEG
127 @ 0.375dB
tATTACK
Limiter Attack Time
tDECAY-DEB
Limiter Decay Debouncing
Time
tDECAY
Limiter Decay Time
Min Typ Max Unit
20 mVP
10 mVP
5 mVP
7.5 kΩ
-7
+33
%
5 pF
-6 +41.6 dB
0.375
dB
0.15 dB
4
ms/
step
0.67 1
0.4 1
41.625
dB
5
µs/
step
64 ms
4
ms/
step
www.austriamicrosystems.com
Revision 1.00
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