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Preliminary
AS2520/21/20B/21B
Telephone Speech Circuit with Loudhearing and Handsfree
Austria Mikro Systeme International AG
Key Features
u Line/speech circuit, loudhearing, handsfree and dc/dc converter on one 28 pin CMOS chip u Operating range from 13 to 100 mA (down to 5 mA with reduced performance) u Soft clipping control eliminating harsh distortion u Volume control of receive signal with squelch and automatic loop gain compensation u Line loss compensation pin selectable u Low noise (max. - 72 dBmp) u Real or complex impedance adjustable u NET 4 compatible u Dynamically controlled voice switching u Same monitor amplifier for loudhearing, handsfree and tone ringer u Very few external components u Power derived from ring signal by switching converter during ringing
General Description
The AS2520/21/20B/21B are CMOS integrated circuits that contain all the audio functions needed to form a high comfort, line-powered telephone. The devices incorporate line adaptation, speech circuit, loudhearing and handsfree - all supervised by the novel voice and power control circuit. A switching converter is also provided for converting the ring signal. The interface to a dialler/controller is made very simple to allow easy adaptation to a telecom microcontroller. The AS2520 series incorporate volume control for the earpiece and the loudspeaker (AS2520 digital with +/keys and AS2521 analogue with potentiometer). The volume control circuit automatically compensates the loop gain to ensure acoustic stability.
Typical Application
La
Package
Available in 28 pin SOP and DIP.
Lb
3V
1 4 7
2 5 8 0
3 6 9 #
DIALLER CONTROLLER LCD DRIVER
TELEPHONE SPEECH CIRCUIT WITH LOUDHEARING, HANDSFREE, DC/DC CONVERTER
HSM
*
HFM
AS2520
Figure 1: Typical Handsfree Telephone Application Rev. 5.1 Page 1 May 1999
Preliminary Pin Description
Pin # 1 2 3 Name LS CI RO Type AI AI AO Description Line Current Sense Input This input is used for sensing the line current. Complex Impedance Input
AS2520/21/20B/21B
Input pin for the capacitor in the complex impedance. Receive Output This is the output for driving a dynamic earpiece with an impedance of 140 to 300 ohm. Positive Voltage Supply This is the supply pin for the circuit. Analogue Ground This pin is the analogue ground for the amplifiers. Side Tone Balance Input This is the input for the side tone cancellation network. Line Loss Compensation Selection Pin -6 dB from 45 mA to 75 mA; LLC = VDD: High range -6 dB from 20 mA to 50 mA; LLC = AGND: Low range gain independent of line current; LLC = VSS: No regulation Loudspeaker Amplifier Input This is the input for applying the receive signal to the loudspeaker amplifier. Tone Input This switchable input is intended for transmitting DTMF or other signals like messages on TAMs (Telephone Answering Machines) onto the line in off-hook conditions and when in ringing mode to apply a PDM signal to the loudspeaker (see also table 1). Receive Threshold Input The sensibility of the receive peak detector can be adjusted by applying the signal from RO to the RTH input through a voltage divider. Converter Make Output This is an output for controlling the external switching converter. It converts the ring signal into a 4V supply voltage and is activated when PD = high and HS, LE, MT = low. Loudspeaker Power Supply High power supply for the output driver stage. Output for Loudspeaker Output pin for an ac coupled 32 (25 to 50 )loudspeaker. Negative High Power Supply This pin is the negative high power supply for the loudspeaker amplifier. Mute Input Dialling mute input (see also table 1). MT = VDD: Tx and Rx channels muted; MT = VSS: Tx and Rx channels not muted. Power Down Input Input for powering down the speech circuit and loudhearing/handsfree (see table 1). Loudhearing Enable Input Input for enabling loudhearing/handsfree, active high (see table 1). Handset Switch Input This is an input that is pulled high by the hook switch (handset) or C when off-hook (see table 1). Page 2 May 1999
4 5 6 7
VDD AGND STB LLC
Supply Supply AI DI
8
LSI
AO
9
TI
AI DI
10
RTH
AI
11
CM
AO
12 13 14 15
VPP LO VSSP MT
Supply AO Supply DI
16
PD
DI
17 18
LE HS
DI DI
Rev. 5.1
Preliminary
19 22 20 21 23 M1 M2 M4 M3 VOL AI AI D/AI
AS2520/21/20B/21B
Microphone Inputs Differential inputs for handset microphone (electret). Handsfree Microphone Inputs These are the input pins for the handsfree microphone (electret). Volume Control Input Volume control for the receive signal. AS2520: Digital control with +/- keys or from C; AS2521: Analogue dc control with potentiometer. Supply Source Control Output This N-channel open drain output controls the external high power source transistor for supplying (VPP) the loudspeaker amplifier in off-hook loudhearing/handsfree mode. Current Shunt Control Output This N-channel open drain output controls the external high power shunt transistor for the modulation of the line voltage and for shorting the line during make period of pulse dialling. Negative Power Supply Line Input This input is used for power extraction and line current sensing. Receive Input This is the input for the receive signal.
AI: AO: AI/O: Analogue Input Analogue Output Analogue Input/output
24
SS
AO
25
CS
AO
26 27 28
DI: DO: DI/O:
VSS LI RI
Supply AI/O AI
Digital Input Digital Output Digital Input/Output
Operating Modes
I/O Pins MODE Idle (on-hook) Ringing POT POT/pulse dialling POT/DTMF dialling Handsfree Handsfree/pulse dial Handsfree/DTMF dial Loudhearing Loudhearing/pulse dial Loudhearing/DTMF dial TAM without LSP TAM with LSP Melody feedback Test mode 1 Test mode 2 HS 0 0 1 1 1 0 0 0 1 1 1 1 1 0 0 0 Digital Inputs LE 0 0 0 0 0 1 1 1 1 1 1 0 1 1 0 0 PD 0 1 0 1 0 0 1 0 0 1 0 1 1 1 0 1 MT 0 0 0 1 1 0 1 1 0 1 1 0 0 0 1 1 Table 1: Operating Modes Rev. 5.1 Page 3 May 1999 Tone Input TI Not connected PDM signal to LO (DI) Not connected Not connected DTMF to LI and RO (AI) Not connected Not connected DTMF to LI and RO (AI) Not connected Not connected DTMF to LI and RO (AI) Signal to LI (AI) Signal to LI (AI) PDM signal to LO (DI) CM Low SW Low Low Low Low Low Low Low Low Low Low Low Low LI `M1/M2' VBE `TI' `M3/M4' VBE `TI' `M1/M2' VBE `TI' `RI/STB' `RI/STB' `RI/STB' `LSI' `LSI' `RI/STB' Outputs RO PD `RI/STB' `TI' `RI/STB' LO PD `TI' `LSI' `LSI' `LSI'
Reserved for testing Reserved for testing
Preliminary Functional Description
The AS252x contains all the voice circuits needed in a high feature telephone instrument, i .e.:
* line adaptation (ac impedance, dc characteristics, 2/4-wire conversion, power extraction) * handset speech circuit * loudhearing with enhanced anti-Larsen * handsfree with dynamic loop gain control * switching converter
AS2520/21/20B/21B
The handset speech circuit consists of a transmit and a receive path with mute, dual soft clipping and line regulation (pin option). A volume control is provided with squelch and loop gain compensation to improve signal-to-noise ratio and to assure acoustic stability. Loudhearing and handsfree functions are also provided. The loudhearing function includes an antiLarsen circuit to prevent acoustic howling. The handsfree circuit has a novel voice control system which is virtually independent of any background noise and works in a dynamic half duplex mode as close to full duplex as the acoustic loop gain allows. The switching converter is used to extract the available power from the ring signal and provides a 4V supply voltage. This allows the same loudspeaker to be used for loudhearing/handsfree and tone ringing.
The line adaptation includes line driver, ac impedance (return loss), 2 to 4 wire converter, dc mask and power extraction circuit for extracting the maximum dc power from the line to supply the whole device and peripheral circuits.
CI 30 L+
SS
VPP M1 MI-AMP TX-AGC M3 LEVEL DETECTOR MI-AMP M4 LEVEL DETECTOR RTH AGND M2
LI LINE DRIVER IMPEDANCE SYNTESIZER CS POWER EXTRACTION
MT or PD
HS
LLC
VDD
LS
DC CONTROL
VOICE & POWER CONTROL
AGND RO-AMP
VDD 300 Vss RI STB
PD VDD
RO
AS2520/21/20B/21B
ST-AMP RX-AGC
MT VPP A PDM INPUT LO-AMP
LSI
LO
ZB
SWITCHING CONVERTER
LOGIC INTERFACE
RING
CM
PD
LE
HS
MT
VOL
TI
VssP
Figure 2: Block Diagramme
Rev. 5.1
Page 4
May 1999
Preliminary
DC Conditions The normal operating range (off-hook) is from 13 mA to 100 mA. Operating range with reduced performance is from 5 mA to 13 mA (parallel operation). In the normal operating range all functions are operational. In the line hold range from 0 to 5 mA the device is in a power down mode and the voltage at LI is reduced to maximum 3.5V. The dc characteristic (excluding diode bridge) is determined by the voltage at LI and the resistor R1 at line currents above 13 mA as follows: VLS = VLI + ILINE R1 The voltage at LI is 4.5V. Below 13 mA the AS252x provides an additional slope in order to allow parallel operation (see figure 3).
8 (V) 7
AS2520/21/20B/21B
(see application notes). The dc resistance of R1 should be kept at 30 ohm to ensure correct dc condition. Return loss and sidetone cancellation can be determined independent of each other (see figure 4). Speech Circuit The speech circuit consists of a transmit and a receive path with soft clipping, mute, line loss compensation and sidetone cancellation. Transmit The gain of the transmit path is 36.5 dB in handset mode (from M1/M2 to LS) and 46.5 dB in handsfree mode (from M3/M4 to LS). The microphone inputs have an input impedance of 15 kohm. The unique dual soft clipping control circuit limits the output voltage at LI to 2VPEAK. Dual means that the soft clipping incorporates both a very fast control circuit to eliminate harsh sidetone distortion and a slower regulation circuit to limit the output voltage at 2VPEAK independent of the line impedance. The attack time is 30 s/6 dB. The overdrive range is 30 dB. When mute is active, pin MT high, the gain is reduced by > 60 dB. Receive The gain of the receive path is 3 dB (test circuit figure 8) from RI to RO. The receive input is the differential signal of RI and STB. Also the receive channel provides soft clipping to avoid acoustic shock and harsh distortion. When mute is active during dialling the gain is reduced by > 60 dB. During DTMF dialling a MF comfort tone is applied to the receiver. The comfort tone is the DTMF signal with a level that is -30 dB relative to the line signal. Volume Control On the AS2520 the receive gain can be changed by pressing the volume keys. The + key increases the gain by 10 dB in 5 steps and the - key decreases the gain by 10 dB in 5 steps. The gain is reset by next off-hook. The volume can also be controlled via a microcontroller. The AS2521 uses a potentiometer to control the receive gain. The volume is an indirect dc control to avoid that noise is introduced from the potentiometer. The volume control is common for both the earpiece and the loudspeaker. Any increase will be compensated to ensure acoustic stability. Page 5 May 1999
VLS
6 5 4 3 2 1 0 0 10 20 30 40 50 Line Current 60 70 80 90 (mA) 100
VLI
Typically No ac signals Tamb: 25C
Figure 3: DC Mask When the PD pin is high (during pulse dialling) the speech circuit and other part of the device not operating are in a power down mode to save current. The CS pin is pulled to VSS in order to turn the external shunt transistor on to keep a low voltage drop at the LS pin during make periods. AC Impedance The synthesised ac impedance of the circuit is set on chip and by an external resistor and an external capacitor (for complex impedance). When R1 is set to 30 ohm, the ac impedance is 1000 ohm real, and the complex part can be set by a capacitor connected to pin 2 (CI). For 600 ohm telephones it is recommended to connect a resistor and a capacitor from pin LS to VSS Rev. 5.1
Preliminary
The acoustic stability is provided as follows: When the volume is increased, e.g. by 10 dB, the receive gain maintains the same as long as no receive signal is applied. Applying a receive signal will cause a 10 dB increase of the receive gain and a corresponding decrease of the transmit gain. This squelch function improves the signal-to-noise ratio. In other words, a certain increase of the volume introduces a similar amount of dynamic voice switching, controlled by the receive signal, also in the handset mode. Sidetone A good sidetone cancellation is achieved by using the following equation: ZBAL/ZLINE = R5/R1 The sidetone cancellation signal is applied to the STB input. By using two separate Wheatstone Bridges for return loss and sidetone cancellation it is very easy to calculate the sidetone balance network (see figure 4). This unique configuration provides a sidetone cancellation less sensitive to tolerances on the external balance network and totally independent of the ac impedance and its tolerances. A good and stable sidetone cancellation improves the handsfree function considerably and ensures a safe margin against acoustic instability under all circumstances.
R1 30 ohm
AS2520/21/20B/21B
20 to 50 mA or 45 to 75 mA depending on selected range. Loudhearing The loudhearing mode is enabled when HS and LE are high. In order to prevent acoustic coupling between the handset microphone and the loudspeaker, the AS252x incorporate an anti-Larsen circuit. The anti-Larsen circuit decreases the gain of the loudspeaker amplifier when a microphone signal is applied. If no signal is applied from the microphone, the loudspeaker amplifier is at its full gain. Anti-Clipping (not AS2520B/21B) The anti-clipping circuit is activated in loudhearing and handsfree mode. The circuit prevents harsh distortion at very high signal levels. Furthermore, the circuit assures that the integrity of the whole telephone circuit is maintained under extreme load conditions, since it prevents that the supply voltage drops below a certain minimum level. The attack time is fast (120 s/6 dB) for preventing harsh distortion when the amplitude rapidly increases. For avoiding chopper effects and to assure low distortion, the decay time is longer, approx. 128 ms/6 dB. When the anti-clipping circuit has been activated by a large receive signal, the channel control will increase the Tx gain corresponding to the reduction in Rx gain caused by the anti-clipping. Handsfree The handsfree function allows voice communication without using the handset (full 2-way speaker phone). Two voice controlled attenuators prevent acoustic coupling between the loudspeaker and the microphone. A conventional voice switching circuit has a channel control with three states, namely idle, transmit or receive. In idle state, when no signal is applied, both the transmit and the receive channels are attenuated by approx. 20 dB to keep the total loop gain below 0 dB. When a signal is applied to the microphone, the circuit switches to transmit state, i.e. the gain in the transmit channel is increased and the gain in the receive channel is decreased accordingly. And vice versa when a receive signal is applied.
ZLINE
ZBAL
R5 300 ohm
Figure 4: Sidetone Bridge Furthermore, the dual Wheatstone bridge makes it very simple to adapt the circuit to different PTT requirements as these two parameters (return loss and sidetone balance) are independent of each other. Line Loss Compensation The line loss compensation (Rx and Tx AGC controlled by the line current) is a pin option. When it is activated, the transmit and receive gains are changed by -6 dB in 1 dB steps at line currents from
Rev. 5.1
Page 6
May 1999
Preliminary
This approach has some disadvantages. It requires a high degree of discipline, since the three state channel control gives a very distinct half duplex with a relative high switching time constant to avoid chopper effects. Furthermore, the system is very sensitive to the environment,- noise, line conditions and acoustics (echo). Apart from keeping a distinct discipline, the user can not do anything to minimise the effect of these constraints, since the parameters of the voice switching (thresholds, time constants, noise discrimination, etc.) can not be changed or adapted to the actual conditions by the user. The dynamic voice control system of the AS252x have been designed to overcome the above constraints. The basic philosophy behind the AS252x is that telephone circuits should not have any automatic regulations preventing the user from having all information about the actual conditions which should enable her/him to act accordingly, i.e. to comply with the given constraints. Now, assuming subscriber A has a handsfree telephone and is calling subscriber B, who has a normal telephone. The B subscriber does not necessarily know that A is using a handsfree telephone and will therefore not automatically comply to the discipline of a half duplex conversation. Hence, the disadvantages by using half duplex should apply to the A subscriber only. Secondly, if A is in a noisy environment, the B subscriber should hear it, so that he speaks up to increase the signal-to-noise ratio at the A subscriber. The traditional 3-state switching system has two major drawbacks: first of all, when no one is talking, the circuit is in idle state and the B subscriber gets the feeling that the line is dead, since the background noise does not activate the voice switching. Secondly, the B subscriber does not speak up, since she/he does not hear the background noise. The concept of the AS252x, however, does not exclude the human factor, but provides the information about the actual conditions to the user and allows her/him to act accordingly, i.e. to speak up, to change the volume, etc. In more technical terms, the AS252x works in the following manner: When no signal is applied neither from the line nor from the microphone, the circuit is in the only static state, which is transmit channel full open and receive channel attenuated by up to 30 dB. Rev. 5.1 Page 7
AS2520/21/20B/21B
The advantages of using the transmit state as the static (idle) state are that the B subscriber hears an open line (the line is not dead), does not miss the initial word of a sentence when the A subscriber starts talking, and hears the level of the background noise at As end which will actuate her/him to speak up accordingly. When the A subscriber starts talking, the circuit remains in the static state. The dynamic state of the voice switching can only be activated by the receive signal. Applying a receive signal above a certain level will cause the circuit to enter the dynamic state.
VTX SIDE TONE
AGC
PEAK DETECTOR VTH
ZAC 2/4
VLINE
VRX 10 dB
VOL
Figure 5: Channel Control System The signal for controlling the channel attenuation is taken after the sidetone amplifier. With the volume at 0 dB (neutral) the threshold for entering the dynamic state (VTH) is 15 mV assuming that VRX > VTX (see figure 5). In the dynamic state the channel attenuation is controlled by a voltage controlled amplifier. The attack time is 4 ms/6 dB and the hold time is 200 ms. A speech compression is activated when a transmit signal with a high amplitude reaches a level corresponding to approximately 460 mV on the line.
300 (mV) 250 Line Output Signal 200 150 100 50 0 0.00 Sidetone Cancellation: 11 dB Volume Control: 0 dB (neutral)
0.25
0.50
0.75
1.00
1.25 (mV)
1.50
Microphone Input Signal
Figure 6: Speech Compression May 1999
Preliminary
The speech compression allows a higher gain in the transmit channel, i.e. the microphone gets more sensitive at low sound pressure levels on the microphone, which enables the user to move further away from the telephone. This means that a constant signal is provided on the line practical independent of the microphone signal level. Any reduction of gain by the compressor in the transmit channel will automatically be given to the receive channel. Switching Converter The ac ringing signal is utilised to extract the power necessary to the tone ringer circuit. A switch mode power supply is used to obtain a high efficiency dc conversion. This approach allows the use of the same loudspeaker and amplifiers for both loudhearing and tone ringing. It also allows an acoustic feedback of the melodies during programming with the same sound pressure level as during ringing. When a ringing signal is applied, PD is pulled high and the oscillator is enabled. The switching converter is controlled by the output CM, which is turned high and low with a duty cycle controlled by the voltage at VPP. When off-hook the switching converter has a high impedance (CM low) to avoid any influence on the transmission and on pulse dialling.
AS2520/21/20B/21B
The smoothing capacitor should be in the range of 10 to 68 nF. The choke coil must have an inductance of >1mH and a dc resistance of < 15 ohm.
15 La 510
Lb 15 510 33 n 30V BC 327
5k6
10 k BC 547 2.2 mH
CM
VPP 470 5V1
VPP VssP
Figure 7: Switching Converter Tone Input The tone input is a digital input in ringing mode and during melody feedback. The digital melody signal (PDM = pulse density modulation) is directly applied to the TI input (see also application notes for further details). During DTMF dialling the DTMF signal is applied through a capacitor to the TI input and will be fed to the line (pin LI) and to the receive output (RO) as confidence tone.
Rev. 5.1
Page 8
May 1999
AS252x
Preliminary Electrical Characteristics
Absolute Maximum Ratings*
AS2520/21/20B/21B
Supply Voltage............................................................................................................................... -0.3 VDD 7V Input Current..........................................................................................................................................+/- 25 mA Input Voltage (LS) ....................................................................................................................... -0.3V VIN 10V Input Voltage (LI, CS, SS).............................................................................................................-0.3V VIN 8V Input Voltage (STB, RI).........................................................................................................-2V VIN VDD +0.3V Digital Input Voltage .......................................................................................................... -0.3V VIN VDD + 0.3V Electrostatic Discharge ..........................................................................................................................+/- 1000V Storage Temperature Range........................................................................................................... -65 to +125C Total Power Dissipation ............................................................................................................................ 500mW
*Exceeding these figures may cause permanent damage. Functional operation under these conditions is not permitted.
Recommended Operating Range Symbol VDD VPP TAMB Parameter Conditions Min. 3.0 3.0 -25 Typ.* 4.1 4.1 Max. 5.5 5.5 +70 Units V V C
Supply Voltage (internally generated) Speech mode Supply Voltage (internally regulated) Ambient Operating Temp. Range Speech mode
* Typical figures are at 25C and are for design aid only; not guaranteed and not subject to production testing.
DC Characteristics (ILINE = 15 mA, recommended operating conditions unless otherwise specified) Symbol IDD Parameter Operating Supply Current Conditions HS = high LE = high HS and LE = high PD = high, CM running IDDPD IDD0 V
LI
Min.
Typ. 5 5 5 300 200 1
Max. 7 7 7
Units mA mA A A A A
Power-Down Current Standby Current Line Voltage Output Current, Sink Pin CS, SS Output Current, Sink Pin CM Input Low Voltage Input High Voltage
PD = high All digital inputs = VSS 13 mA< ILINE < 100 mA VOL = 0.4V VOL = 0.4V TAMB = 25C TAMB = 25C VSS 0.8 VDD 4.2
4.5 1.5 1.5
4.8
V mA mA
IOL IOL VIL VIH
0.2 VDD V VDD V
Rev. 5.1
Page 9
May 1999
Preliminary
AC Electrical Characteristics ILINE = 15 mA; f = 800 Hz; recommended operating conditions unless otherwise specified. Transmit Symbol ATX Parameter Gain (M1/M2 to LS) Gain (M3/M4 to LS) AMF
ATX/F
AS2520/21/20B/21B
Conditions HS, LH modes; LLC = AGND HF mode; LLC = AGND MF mode f = 500 Hz to 3.4 kHz Speech mode; LLC = VSS or VDD VLI < 0.25 VRMS HS, LH modes; VLI = HF mode; VLI =
Min. 35 45 12
Typ. 36.5 46.5 13.5 +/- 0.8 -6
Max. 38 48 15
Units dB dB dB dB dB
Gain (TI to LS) Variation with Frequency Gain Range, LLC Distortion Soft Clip Level Soft Clip Level Soft Clip Overdrive Input Impedance; Attenuation Depth Mute Attenuation Noise Output Voltage
ALLC THD VAGC VAGC ASCO ZIN AAD AMUTE VNO
2 2 650 30
% VPEAK mVPEAK dB kohm dB dB
M1/M2 and M3/M4
15 30
Mute activated HS = high; TAMB = 25C LE = high; HS = low; TAMB = 25C
60 -72 -62 +/- 1 +/- 0.5
dBmp dBmp VPEAK VPEAK
VIN MAX
Input Voltage Range; M1/M2
Differential Single ended
Line Driver Symbol VIN MAX RL
ZAC/TEMP
Parameter Input Voltage Range; LI Return Loss Temperature Variation
Test Conditions
Min.
Typ. +/- 2
Max.
Units VPEAK dB
ZRL = 1000 ohm; TAMB = 25C
18 0.5
/C
Rev. 5.1
Page 10
May 1999
Preliminary
Receive Symbol ARX Parameter Gain (LS to RO), Default LSP Gain (LSI to LO)
ATX/F
AS2520/21/20B/21B
Condition Volume reset
Min. 1.5 17.5
Typ. 3 19 +/- 0.8 -6 20
Max. 4.5 20.5
Units dB dB dB dB dB
Variation with Frequency Gain Range, LLC Volume Range Distortion Soft Clip Level (RO) Soft Clip Level (LO)
f = 500 Hz to 3.4 kHz Speech mode; LLC = VSS or VDD 10 steps, each 2 dB VRI < 0.2 VRMS VRO = Not AS2520B/21B; VLO = Unloaded
ALLC ARX THD VSC
2 1 1.3
% VPEAK VPEAK
ASCO VRTH AAD tDECAY tDECAY VNO VUFC ZIN VIN RI AST ZIN VIN ST
Soft Clip Overdrive Threshold Voltage at RTH Attenuation Depth Attack Time Decay Time Channel control; VRI > 0.8 VRMS Channel control 7
30 15 30 25
dB mV dB s/6dB s/6dB -72 -60 dBmp dBmp kohm VPEAK dB
Noise Output Voltage (RO) HS = high; TAMB = 25C Unwanted Frequency Components (RO) Input Impedance, RI Input Voltage Range, RI Sidetone Cancellation Input Impedance, STB Input Voltage Range, STB VRI < 0.2 VRMS; TAMB = 25C 26 80 +/- 2 50 Hz.........20 kHz 8 +/- 2
kohm VPEAK
General Timings Symbol tVOL tSCA tSCD tPDA tPDD tLPA tLPD Parameter Volume Key Debounce Soft Clip Attack Time Soft Clip Decay Time VIN above soft clip level VIN below soft clip level Condition Min. Typ. 7 0.12 128 3.2 29 250 1 Max. Units ms ms/6dB ms/6dB ms/V ms/V ms/6dB sec/6dB
Peak Detector Attack Time VIN above VTH Peak Detector Decay Time VIN below VTH Low-Power Attack Time Low-Power Release VPP < 3.6V VPP > 3.6V
Rev. 5.1
Page 11
May 1999
11 CM 2 CI A 1 LS 10 100 30 ohm RI M1 6 STB M2 22 300 ohm UL 10 V B 21 27 LI 25 CS M4 AGND 5 10 10 RTH 25 ohm 13 LO 14 VsSP 3 RO 16 PD LSI 18 17 1k HS LE TI 9 1k 15 MT 4 VDD 7 LLC 23 VOL 22 200 ohm 26 Vss 20 BC 327 M3 1k 6k 680 n 19 1k 28
Rev. 5.1
600 ohm 24 SS BC 327
Preliminary
Test Circuit
ILINE
AS252x
Figure 8: Test Circuit
Page 12
12 VPP 22
8
AS2520/21/20B/21B
May 1999
Preliminary Application Diagramme
La 30
AS2520/21/20B/21B
2k2
Lb
10 V 27 LI CI 25 BC327 26 1 LS 28 10 VDD 4 VDD CS M1 Vss 19 15 n 220 2 1k2
LINE ADAPTER/TELEPHONE VOICE CIRCUIT
22 M2
15 n
RI
1k2 1 6 STB 1k8 Side tone balance network 10 n 10 RO 3 300
7k5
9 INPUT FOR DTMF AND TONE RINGER MELODIES TI 33 n
18 16 CONTROL INPUTS (FROM C) 15
HS PD MT
8 LSI
100 n
100 n
10 RTH 1k8 M3 21 100 n
17 15 15
LE
510
510
5 AGND 100 M4 20 100 n 1k8 100 LO 13 32
24 33 n MPSA92 11 2N5551 CM 5k6 BC327 10 k SS
AS252x
High 7 LLC Low Off AGND
VDD
2.2 mH 12 5V1 470 VPP
10 k 23 VOL AS2521 AS2520 100 k VOL+ VOL-
14
VSSP
Figure 9: Application Diagramme
Applications Hints
Interface to Microcontroller In off-hook condition the microcontroller can be supplied from VDD of AS252x. The digital inputs (HS, LE, PD, and MT) must be kept low until VDD has reached its minimum operating voltage (>2.5V). Radio Frequency Interference The RFI sensitivity has been minimised by the consequent use of CMOS technology and one overall ground and by having differential inputs with a relative low input impedance. For further application information see application notes for the AS2520 series. Rev. 5.1 Page 13 May 1999
Preliminary Pin Configuration
28 Pin SOP/DIP
AS2520/21/20B/21B Ordering Information
Part Number
28 27 26 25 24 23 22 21 20 19 18 17 16 15 RI LI VSS CS SS VOL M2 M3 M4 M1 HS LE PD MT
Package Type 28 pin SOP 28 pin DIP 28 pin SOP 28 pin DIP 28 pin SOP 28 pin DIP 28 pin SOP 28 pin DIP
Volume Control Digital Digital Digital Digital Analogue Analogue Analogue Analogue
Soft Clip Loudspk. Yes Yes No No Yes Yes No No
LS CI RO VDD AGND STB LLC LSI TI RTH CM VPP LO VSSP
1 2 3 4 5 6 7 8 9 10 11 12 13 14
AS2520 T AS2520 P AS2520B T AS2520B P AS2521 T AS2521 P AS2521B T AS2521B P
The devices are also available as dice on request.
Devices sold by Austria Mikro Systeme Int. AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. Austria Mikro Systeme Int. AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement Austria Mikro Systeme Int. AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with Austria Mikro Systeme Int. AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or life-sustaining equipment are specifically not recommended without additional processing by Austria Mikro Systeme Int. AG for each application. Copyright (c) 1999, Austria Mikro Systeme International AG, Schloss Premstatten, 8141 Unterpremstatten, Austria. Trademarks Registered(R). All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner. Austria Mikro Systeme Int. AG reserves the right to change or discontinue this product without notice.
Rev. 5.1
AS252x
Page 14
May 1999

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