MT91600AN

MT91600 Programmable SLIC Data Sheet Features • • • • • • • • • Transformerless 2 W to 4 W conversion Controls battery feed to line Programmable line impedance Programmable network balance impedance Off-hook and dial pulse detection Ring ground over-current protection Programmable gain Programmable constant current feed -22 V to -72 V battery operation Ordering Information MT91600AN MT91600ANR MT91600AN1 MT91600ANR1 *Pb 28 Pin SSOP 28 Pin SSOP 28 Pin SSOP* 28 Pin SSOP* Free Matte Tin Tubes Tape & Reel Tubes Tape & Reel February 2005 -40° C to +85 ° C Description The Zarlink MT91600 provides an interface between a switching system and a subscriber loop, mainly for short loop SLIC applications. The functions provided by the MT91600 include battery feed, programmable constant current, 2 W to 4 W conversion, off-hook and dial pulse detection, user definable line and network balance impedance’s and the capability of programming the audio gain externally. The device is fabricated as a CMOS circuit in a 28 pin SSOP package. Applications Line interface for: • • • • PABX/ONS Intercoms Key Telephone Systems Control Systems X3 X2 X1 TD Tip Drive Controller Audio Gain & Network Balance Circuit VX VR TF TIP RING RF C3A C3B RV RD Over-Current Protection Circuit Relay Driver Ring Drive Controller Loop Supervision Line Sense 2 W to 4 W Conversion & Line Impedance Z3 Z2 Z1 RLYC RLYD IC VREF SHK C1 C2A C2B VDD GND VEE Figure 1 - Functional Block Diagram 1 Zarlink Semiconductor Inc. Zarlink, ZL and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc. Copyright 1999-2005 Zarlink Semiconductor Inc. All Rights Reserved. MT91600 Change Summary Page 10 Item Figure 5 Change Updated Application Diagram Data Sheet VDD TD TF TIP RING VREF IC RF RV RD C3A C3B C2B C2A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 VEE GND RLYD RLYC SHK C1 X2 VR X3 VX X1 Z3 Z2 Z1 Figure 2 - Pin Connections Pin Description Pin # 1 2 3 4 5 6 Name VDD TD TF TIP RING VREF Positive supply rail, +5 V. Tip Drive (Output). Controls the Tip transistor. Tip Feed. Connects to the Tip transistor and to the TIP lead via the Tip feed resistor. Tip. Connects to the TIP lead of the telephone line. Ring. Connects to the RING lead of the telephone line. Reference Voltage (Input). This pin is used to set the subscribers loop constant current. Changing the input voltage sets the current to any desired value within the working limits. VREF is related to VLC. Internal Connection (Input). This pin must be connected to GND for normal operation. Ring Feed. Connects to the RING lead via the Ring feed resistor. Ring Voltage and Audio Feed. Connects directly to the Ring drive transistor and also to Ring Feed via a relay. Ring Drive (Output). Controls the Ring transistor. A filter capacitor for over-current protection is connected between this pin and GND. A filter capacitor for over-current protection is connected between this pin and GND. A capacitor for loop current stability is connected between this pin and C2A. A capacitor for loop current stability is connected between this pin and C2B. Line Impedance Node 1. A resistor of scaled value "k" is connected between Z1 and Z2. This connection can not be left open circuit. Description 7 8 9 10 11 12 13 14 15 IC RF RV RD C3A C3B C2B C2A Z1 2 Zarlink Semiconductor Inc. MT91600 Pin Description (continued) Pin # 16 17 18 19 20 21 22 23 24 25 26 27 28 Name Z2 Z3 X1 VX X3 VR X2 C1 SHK RLYC RLYD GND VEE Description Data Sheet Line Impedance Node 2. This is the common connection node between Z1 and Z3. Line Impedance Node 3. A network either resistive or complex of scaled value "k" is connected between Z3 and Z2. This connection can not be left open circuit. Gain Node 1. This is the common node between Z3 and VX where resistors are connected to set the 2 W to 4 W gain. Transmit Audio (Output). This is the 4 W analog signal to the SLIC. Gain Node 3. This is the common node between VR and the audio input from the CODEC or switching network where resistors are fitted to sets the 4 W to 2 W gain Receive Audio (Input). This is the 4 W analog signal to the SLIC. Gain Node 2. Networks, either resistive or complex, are connected between this node, VR and GND to set the Network Balance Impedance for the SLIC. A filter capacitor for ring trip is connected between this pin and GND. Switch Hook (Output). This pin indicates the line state of the subscribers telephone. The output can also be used for dial pulse monitoring. SHK is high in off-hook state. Relay Control (Input). An active high on this pin will switch RLYD low. Inverted Output of RLYC. It is used to drive the bipolar transistor that drives the relay (see Figure 5.) Ground. Return path for +5 V and -5 V. This should also be connected back to the return path for the loop battery, LGND and relay drive ground RLYGND. Negative supply rail, -5 V. Functional Description The MT91600 is the analog SLIC for use in a 4 Wire switched system. The SLIC performs all of the normal interface functions between the CODEC or switching system and the analog telephone line such as 2 W to 4 W conversion, constant current feed, ringing and ring trip detection, current limiting, switch hook indication and line and network balance impedance setting using minimal external components. Refer to Figure 5 for MT91600 components designation. 2 Wire to 4 Wire Conversion The hybrid performs 2 wire to 4 wire conversion by taking the 4 wire signal from an analog switch or voice CODEC, a.c. coupled to VRIN, and converting it to a 2 wire differential signal at tip and ring. The 2 wire signal applied to tip and ring by the telephone is converted to a 4 wire signal and should be a.c. coupled to Vx which is the output from the SLIC to the analog switch or voice CODEC input. Gain Control It is possible to set the Transmit and Receive gains by the selection of the appropriate external components. The gains can be calculated by the formulae: 2W to 4W gain: Gain 2 - 4 = 20*Log [ R13 / R12] 4W to 2W gain: Gain 4 - 2 = 20*Log [0.891 * (R14 / R15)] 3 Zarlink Semiconductor Inc. MT91600 Impedance Programming Data Sheet The MT91600 allows the designer to set the device’s impedance across TIP and RING, (ZTR), and network balance impedance, (ZNB), separately with external low cost components. For a resistive load, the impedance (ZTR) is set by R11 and R18. For a complex load, the impedance (ZTR) is set by R11, R18, R19 & C8 (see Figure 5.) The network balance, (ZNB), is set by R16, R17 & C3 (see Figure 5.) The network balance impedance should be calculated once the 2W - 4W gain has been set. Line Impedance For optimum performance, the characteristic impedance of the line, (Zo), and the device’s impedance across TIP and RING, (ZTR), should match. Therefore: Zo = ZTR The relationship between Zo and the components that set ZTR is given by the formula: Zo / ( R1+R2) = kZo / R11 where kZo = ZLZ ZLZ = R18, for a resistive load. ZLZ = [R18 + (R19 // C8)], for a complex load. The value of k can be set by the designer to be any value between 20 and 250. Three rules to ensure the correct operation of the circuit: (A) R18 + R19 > 50kΩ (B) R1 = R2. (C) R11 > =50kΩ It is advisable to place these components as close as possible to the SLIC. Network Balance Impedance The network balance impedance, (ZNB), will set the transhybrid loss performance for the circuit. The balance of the circuit is independent of the 4 - 2 Wire gain but is a function of the 2 - 4 Wire gain. The method of setting the values for R16 and R17 is given by the formula: R17 = [1.782 * Zo / ( Zo+ZNB) * ( R13 / R12 )] R17 + R16 [1 + R13 / R12] where ZNB is the network balance impedance of the SLIC and Zo is the line impedance. (R16 + R17) >= 50kΩ It is advisable to place these components as close as possible to the SLIC. 4 Zarlink Semiconductor Inc. MT91600 Loop Supervision & Dial Pulse Detection Data Sheet The Loop Supervision circuit monitors the state of the phone line and when the phone goes "Off Hook" the SHK pin goes high to indicate this state. This pin reverts to a low state when the phone goes back "On Hook" or if the loop resistance is too high for the circuit to continue to support a constant current. The SHK output can also be monitored for dialing information when used in a dial pulse system. Constant Current Control The SLIC employs a feedback circuit to supply a constant feed current to the line. This is done by sensing the sum of the voltages across the feed resistors, R1 and R2, and comparing it to the input reference voltage, Vref, that determines the constant current feed current. The MT91600’s programmable current range is between 18 mA to 32 mA. Line Drivers & Overcurrent Protection The Line Drivers control the external Battery Feed circuit which provide power to the line and allows bi-directional audio transmission. The loop supervision circuitry provides bias to the line drivers to feed a constant current while the over-current protection circuitry prevents the ring driver from causing the ring transistor to overload. The line impedance presented by the Line Driver circuitry is determined by the external network, which may be purely resistive or complex, allowing the circuit to be configured for use in any application. The impedance can also be fixed to one value and modified to look like a different value by reflecting an impedance through the SLIC from an intelligent CODEC or DSP module. There is long term protection on the RING output against accidental short circuits that may be applied either across TIP/RING to GND or RING to GND. This high current will be sensed and limited to a value that will protect the circuit. In situations where an accidental short circuit occurs either across TIP/RING to GND or RING to GND, an excessive amount of current will flow through the ring drive transistor, Q3. Although the MT91600 will sense this high current and limit it, if the power rating of Q3 is not high enough, it may suffer permanent damage. In this case, a power sharing resistor, R23, can be inserted (see Figure 5) to dissipate some of the power. Capacitor C13 is inserted to provide an a.c. ground point. The criteria for selecting a value for the power sharing resistor R23 can be found in the application section of this data sheet. Ringing and Ring Trip Detection Ringing is applied to the line by disconnecting pin 8, RF, from pin 9, RV, and connecting it to a ringing source which is battery backed. This may be done by use of an electro-mechanical relay. The SLIC is capable of detecting an Off Hook condition during ringing by filtering out the large A.C. component by use of the external components connected to pin 23. This filter allows an Off Hook condition to be monitored at SHK, pin 24. When using DTMF signalling only i.e., pulse dialling is not used, the capacitor, C7, can be permanently connected to ground and does not require to be switched out during dialling. Power up Sequence The circuit should be powered up in the following order: AGND, VEE, VDD, VBAT. 5 Zarlink Semiconductor Inc. MT91600 Application Data Sheet The following Application section is intended to demonstrate to the user the methods used in calculating and selecting the external programming components in implementing the MT91600 as an analog line interface in a communication system. The programming component values calculated below results in the optimum performance of the device. Refer to Figure 5 for MT91600 components designation. Component Selection Feed Resistors (R1, R2) The selection of feed resistors, R1 and R2, can significantly affect the performance of the MT91600. It is recommended that their values fall in the range of: 200Ω