HC5549 Semiconductor Data Sheet January 1999 Low Power SLIC with Battery Switch Features The HC5549 Subscriber line interface circuit is a 100V diellectrically isolated bipolar integrated circuit for use in short loop ISDN, PABX and Pairgain applications. The HC5549 has been optimized for low power as required for battery backed remote terminals or for applications requiring emergency powering from the line such as European ISDN NT1+ designs. • Dual Battery Operation File Number 4539.1 • Single Additional +5V Supply • Low Standby Power Consumption (48V, 35mW) • On Hook Transmission • Tip and Ring Disconnect • Soft or Hard Polarity Reversal • Supports 12 kHz or 16 kHz Pulse Metering A high and low voltage battery supply may be connected to the HC5549 so that power dissipation can be lowered in the off hook condition in these short loop applications. The high battery supply can be used in the on-hook condition to allow interfacing to fax and answering machines that require 48V to detect end of call status. The HC5549 also has a low power standby state with very low power consumption (35mW) resulting in exceptionally low battery drain while providing continued loop supervision. • Ring Relay Driver • On Chip 2-wire AC/DC Loopback • No Latch-Up or Power Supply Sequencing • 0o to 70o or -40o to 85o Ambient Temp Range • Low External Component Count Applications The HC5549 provides loop current, ground key and ring trip detect functions as well as an alarm output to indicate thermal overload. • ISDN NT1+ Terminals • Pairgain Remote Termination • PABX and Key Systems 2-wire to 4-wire and 4-wire to 2-wire conversion is provided and impedance matching is achieved using a single external network. The HC5549 is compatible with dual and single supply switched capacitor or DSP codec/filters Related Literature • AC SPICE Macromodel Block Diagram POL ILIM TIP RING SW+ SW- CDC VBL VBH DC CONTROL BATTERY SWITCH RINGING PORT VRS 2-WIRE PORT TRANSMIT SENSING 4-WIRE PORT VRX VTX -IN VFB TEST ACCESS DETECTOR LOGIC CONTROL LOGIC RTD RD E0 DET ALM 4-80 BSEL F2 F1 F0 SWC CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-800-4-HARRIS or 407-727-9207 | Copyright © Harris Corporation 1999 RSLIC18™ is a trademark of Harris Corporation. HC5549 Ordering Information (PLCC Package Only) 48V BAT SW POL REV RING DELAY DRIVER 2W LOOP BACK LB = 53dB TEMP. RANGE oC PACKAGE PACKAGE NO. HC5549CM • • • • • • 0 to 70 28 Ld PLCC N28.45 HC5549IM • • • • • • -40 to 85 28 Ld PLCC N28.45 PART NUMBER Device Operating Modes OPERATING MODE F2 F1 F0 E0 = 1 E0 = 0 Low Power Standby 0 0 0 SHD GKD MTU compliant standby mode with active loop detector. Forward Active 0 0 1 SHD GKD Forward battery loop feed. Unused 0 1 0 n/a n/a Reverse Active 0 1 1 SHD GKD Reverse battery loop feed. Ringing 1 0 0 RTD RTD Enabler internal ring trip detector. Unused 1 0 1 n/a n/a Reserved internal test mode. Unused 1 1 0 n/a n/a Reserved internal test mode. Power Denial 1 1 1 n/a n/a Device shutdown. Pinouts SW+ 4-81 TIP 2 1 ILIM BGND 3 RD VBL 4 RING VBH HC5549 (PLCC) TOP VIEW 28 27 26 5 25 RTD SW- 6 24 CDC SWC 7 23 VCC F2 8 22 -IN F1 9 21 VFB F0 10 20 VTX E0 11 18 VRB AGND 17 POL DET 16 NC 14 15 NC 13 ALM 19 VRX 12 DESCRIPTION Reserved internal test mode. HC5549 Absolute Maximum Ratings TA = 25oC Thermal Information Thermal Resistance (Typical, Note 1) θJA (oC/W) PLCC Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Maximum Junction Temperature Plastic . . . . . . . . . . . . . . . . 150oC Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC (PLCC - Lead Tips Only) Maximum Supply Voltages VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +7V VCC - VBAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80V Uncommitted Switch Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . -80V ESD (Human Body Model). . . . . . . . . . . . . . . . . . . . . . . . . . . . 500V Operating Conditions Temperature Range Industrial (I suffix) . . . . . . . . . . . . . . . . . . . . . . . . . . -40oC to 85oC Commercial (C suffix). . . . . . . . . . . . . . . . . . . . . . . . 0oC to 75oC Positive Power Supply (VCC) . . . . . . . . . . . . . . . . . . . . . . . +5V ±5% Negative Power Supply (VBH, VBL) (180, 181, 182) . . -16V to -80V Uncommitted Switch (loop back or relay driver). . . . . . . +5V to -80V Die Characteristics Substrate Potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VBAT Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bipolar-DI CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. NOTE: 1. θJA is measured with the component mounted on an evaluation PC board in free air. Electrical Specifications Unless Otherwise Specified, TA = -40oC to 85oC, VBL = -24V, VBH = -48V, VCC = +5V, AGND = BGND = 0V, loop current limit = 25mA. All AC Parameters are specified at 600Ω 2-wire terminating impedance over the frequency band of 300Hz to 3.4kHz. Protection resistors = 0Ω. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 480 - - kΩ 160 - - kΩ - - 1 Ω THD = 1% 3.1 3.5 - VPK 2-Wire Port Overload Level THD = 1% 3.1 3.5 - VPK 2-Wire Return Loss 300Hz ≤ f < 1kHz 30 45 - dB 1kHz ≤ f ≤ 3.4kHz 35 45 - dB Test for False Detect - 20 - mARMS Test for False Detect, Low Power Standby, BSEL = 0 - 10 - mARMS RINGING PARAMETERS VRB Input Impedance AC TRANSMISSION PARAMETERS (Forward Active and Reverse Active, BSEL = 0, unless otherwise specified.) Receive Input Impedance Transmit Output Impedance 4-Wire Port Overload Level Longitudinal Current Capability (Per Wire) 2-Wire Longitudinal Balance Tested per IEEE455-1985, with 368Ω per wire. 53 - - dB 4-Wire Longitudinal Balance Tested per IEEE455-1985, with 368Ω per wire. 59 - - dB -6.22 -6.02 -5.82 dB +3 to -40dBm, 1kHz - 0.025 - dB -40 to -50dBm, 1kHz - 0.050 - dB -50 to -55dBm, 1kHz - 0.100 - dB C-Message - 16 19 dBrnC Psophometric - -74 -71 dBmp 15 - 45 mA - - 4-Wire to 4-Wire Insertion Loss 2-Wire to 4-Wire Level Linearity 4-Wire to 2-Wire Level Linearity Referenced to -10dBm Idle Channel Noise 2-Wire DC PARAMETERS Loop Current Limit Programming Range Max Low Battery = -52V, BSEL = 0 Loop Current Accuracy IL = 25mA, BSEL = 0 10 % Loop Current During Low Power Standby Forward polarity only. 17 - 26 mA Open Circuit Voltage (|Tip - Ring|) BSEL = 0 14 15.5 17 V BSEL = 1 37.5 40 42.5 V Low Power Standby Open Circuit Voltage (Tip - Ring) BSEL = 1 43 45 47 V - - Ring Trip Programming Current Accuracy 4-82 10 % HC5549 Electrical Specifications Unless Otherwise Specified, TA = -40oC to 85oC, VBL = -24V, VBH = -48V, VCC = +5V, AGND = BGND = 0V, loop current limit = 25mA. All AC Parameters are specified at 600Ω 2-wire terminating impedance over the frequency band of 300Hz to 3.4kHz. Protection resistors = 0Ω. (Continued) PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 10 12 13.5 mA IC junction temperature - 175 - oC IL = 45 mA - - 0.60 V Input Low Voltage - - 0.8 V Input High Voltage 2.0 - - V Ground Key Threshold Thermal Alarm Output RELAY DRIVER On Voltage LOGIC INPUTS (F0, F1, F2, E0, SWC) Input Low Current VIL = 0.4V -20 - - µA Input High Current VIH = 2.4V - - 5 µA Output Low Voltage IOL = 5mA - - 0.4 V Output High Voltage IOH = 100 µA 2.4 - - V LOGIC OUTPUTS (DET, ALM) SUPPLY CURRENTS (Supply currents not listed are considered negligible and do not contribute significantly to total power dissipation. All measurements made under open circuit load conditions.) Low Power Standby ICC 2.0 3.7 5.0 mA - 0.375 0.600 mA 2.5 4.0 5.0 mA - 1.0 2.0 mA 3.5 4.5 6.5 mA IBL , BSEL = 1 - 0.7 1.5 mA IBH , BSEL = 1 - 1.0 2.0 mA 0.5 3.0 5.0 mA IBL, BSEL = 1 or 0 - 0.2 0.5 mA Forward or Reverse BSEL = 0 - 44 60 mW Forward or Reverse BSEL = 1 - 90 150 mW Low Power Standby BSEL = 1 - 37 60 mW BSEL = 0 - 290 310 mW f = 300Hz - 40 - dB f = 1kHz - 35 - dB f = 3.4kHz - 28 - dB f = 300Hz - 45 - dB f = 1kHz - 43 - dB f = 3.4kHz - 33 - dB VBL to 2-Wire 300Hz ≤ f ≤ 3.4kHz - 30 - dB VBL to 4-Wire 300Hz ≤ f ≤ 3.4kHz - 35 - dB VBH to 2-Wire 300Hz ≤ f ≤ 3.4kHz - 33 - dB VBH to 4-Wire 300Hz ≤ f ≤ 1kHz - 40 - dB 1kHz < f ≤ 3.4kHz - 45 - dB IBH , BSEL = 1 Forward or Reverse (Note 5) ICC IBL , BSEL = 0 Forward ICC Power Denial ICC ON HOOK POWER DISSIPATION OFF HOOK POWER DISSIPATION Forward or Reverse POWER SUPPLY REJECTION RATIO VCC to 2-Wire VCC to 4-Wire 4-83 HC5549 Design Equations 4-WIRE TO 2-WIRE GAIN Loop Supervision Thresholds SWITCH HOOK DETECT The switch hook detect threshold is set by a single external resistor, RSH . Equation 1 is used to calculate the value of RSH. (EQ. 1) R SH = 600 ⁄ I SH The 4-wire to 2-wire gain is defined as the receive gain. It is a function of the terminating impedance, synthesized impedance and protection resistors. Equation 6 calculates the receive gain, G42. ZL G 42 = – 2 ------------------------------------------ Z + 2R O P + Z L (EQ. 6) The term ISH is the desired DC loop current threshold. The loop current threshold programming range is from 5mA to 15mA. When the device source impedance and protection resistors equals the terminating impedance, the receive gain equals unity. GROUND KEY DETECT 2-WIRE TO 4-WIRE GAIN The ground key detector senses a DC current imbalance between the Tip and Ring terminals when the ring terminal is connected to ground. The ground key detect threshold is not externally programmable and is internally fixed to 12mA regardless of the switch hook threshold. The 2-wire to 4-wire gain (G24) is the gain from tip and ring to the VTX output. The transmit gain is calculated in Equation 7. RING TRIP DETECT When the protection resistors are set to zero, the transmit gain is -6dB. The ring trip detect threshold is set by a single external resistor, RRT. IRT should be set between the peak ringing current and the peak off hook current while still ringing. (EQ. 2) R RT = 1800 ⁄ I RT The capacitor CRT, in parallel with RRT, will set the ring trip response time. Loop Current Limit The loop current limit of the device is programmed by the external resistor RIL. The value of RIL can be calculated using Equation 3. 1760 R IL = ------------I LIM (EQ. 3) ZO G 24 = – ------------------------------------------ Z O + 2R P + Z L TRANSHYBRID GAIN The transhybrid gain is defined as the 4-wire to 4-wire gain (G44). ZO G 44 = – --------------------------------------- Z O + 2R P + Z L COMPLEX IMPEDANCE SYNTHESIS Substituting the impedance programming resistor, RS, with a complex programming network provides complex impedance synthesis. 2-WIRE NETWORK C2 R1 The impedance of the device is programmed with the external component RS . RS is the gain setting resistor for the feedback amplifier that provides impedance matching. If complex impedance matching is required, then a complex network can be substituted for RS . RESISTIVE IMPEDANCE SYNTHESIS The source impedance of the device, ZO , can be calculated in Equation 4. (EQ. 4) R S = 400 ( Z O ) (EQ. 5) Z O = Z L – 2R P 4-84 PROGRAMMING NETWORK CP RS R2 RP FIGURE 1. COMPLEX PROGRAMMING NETWORK The reference designators in the programming network match the evaluation board. The component RS has a different design equation than the RS used for resistive impedance synthesis. The design equations for each component are provided below. R S = 400 × ( R 1 – 2 ( R P ) ) The required impedance is defined by the terminating impedance and protection resistors as shown in Equation 5. (EQ. 8) When the protection resistors are set to zero, the transhybrid gain is -6dB. The term ILIM is the desired loop current limit. The loop current limit programming range is from 15mA to 45mA. Impedance Matching (EQ. 7) (EQ. 9) R P = 400 × R 2 (EQ. 10) C P = C 2 ⁄ 400 (EQ. 11) HC5549 Low Power Standby Overview The low power standby mode (LPS, 000) should be used during idle line conditions. The device is designed to operate from the high battery during this mode. Most of the internal circuitry is powered down, resulting in low power dissipation. If the 2-wire (tip/ring) DC voltage requirements are not critical during idle line conditions, the device may be operated from the low battery. Operation from the low battery will decrease the standby power dissipation. TABLE 1. DEVICE INTERFACES DURING LPS INTERFACE ON OFF NOTES Receive x Ringing x AC transmission, impedance matching and ringing are disabled during this mode. Transmit x 2-Wire x Amplifiers disabled. Loop Detect x Switch hook or ground key. 2-WIRE INTERFACE During LPS, the 2-wire interface is maintained with internal switches and voltage references. The Tip and Ring amplifiers are turned off to conserve power. The device will provide MTU compliance, loop current and loop supervision. Figure 2 represents the internal circuitry providing the 2-wire interface during low power standby. GND Ring terminal will be clamped by the internal reference. The same Ring relationships apply when operating from the low battery voltage. For high battery voltages (VBH) less than or equal to the internal MTU reference threshold: V RING = V BH + 4 Loop Current During LPS, the device will provide current to a load. The current path is through resistors and switches, and will be function of the off hook loop resistance (RLOOP). This includes the off hook phone resistance and copper loop resistance. The current available during LPS is determined by Equation 13. I LOOP = ( – 1 – ( – 49 ) ) ⁄ ( 600 + 600 + R LOOP ) TIP AMP TIP RING (EQ. 13) Internal current limiting of the standby switches will limit the maximum current to 20mA. Another loop current related parameter is longitudinal current capability. The longitudinal current capability is reduced to 10mARMS per pin. The reduction in longitudinal current capability is a result of turning off the Tip and Ring amplifiers. On Hook Power Dissipation The on hook power dissipation of the device during LPS is determined by the operating voltages and quiescent currents and is calculated using Equation 14. P LPS = V BH × I BHQ + V BL × I BLQ + V CC × I CCQ 600Ω (EQ. 12) (EQ. 14) The quiescent current terms are specified in the electrical tables for each operating mode. Load power dissipation is not a factor since this is an on hook mode. Some applications may specify a standby current. The standby current may be a charging current required for modern telephone electronics. RING AMP 600Ω MTU REF FIGURE 2. LPS 2-WIRE INTERFACE CIRCUIT DIAGRAM MTU Compliance Maintenance Termination Unit or MTU compliance places DC voltage requirements on the 2-wire terminals during idle line conditions. The minimum idle voltage is 42.75V. The high side of the MTU range is 56V. The voltage is expressed as the difference between Tip and Ring. The Tip voltage is held near ground through a 600Ω resistor and switch. The Ring voltage is limited to a maximum of -49V (by MTU REF) when operating from either the high or low battery. A switch and 600Ω resistor connect the MTU reference to the Ring terminal. When the high battery voltage exceeds the MTU reference of -49V (typically), the 4-85 Standby Current Power dissipation Any standby line current, ISLC , introduces an additional power dissipation term PSLC . Equation 15 illustrates the power contribution is zero when the standby line current is zero. P SLC = I SLC × ( V BH – 49 + 1 + I SLC x1200 ) (EQ. 15) If the battery voltage is less than -49V (the MTU clamp is off), the standby line current power contribution reduces to Equation 16. P SLC = I SLC × ( V BH + 1 + I SLC x1200 ) (EQ. 16) Most applications do not specify charging current requirements during standby. When specified, the typical charging current may be as high as 5mA. HC5549 Forward Active filter is set by the external capacitor CDC . The value of the external capacitor should be 4.7µF. The forward active mode (FA, 001) is the primary AC transmission mode of the device. On hook transmission, DC loop feed and voice transmission are supported during forward active. Loop supervision is provided by either the switch hook detector (E0 = 1) or the ground key detector (E0 = 0). The device may be operated from either high or low battery for onhook transmission and low battery for loop feed. On-Hook Transmission The primary purpose of on hook transmission will be to support caller ID and other advanced signalling features. The transmission over load level while on hook is 3.5VPEAK . When operating from the high battery, the DC voltages at Tip and Ring are MTU compliant. The typical Tip voltage is -4V and the Ring voltage is a function of the battery voltage for battery voltages less than -60V as shown in Equation 17. (EQ. 17) V RING = V BH + 4 Most applications will operate the device from low battery while off hook. The DC feed characteristic of the device will drive Tip and Ring towards half battery to regulate the DC loop current. For light loads, Tip will be near -4V and Ring will be near VVBL + 4V. The following diagram shows the DC feed characteristic. VTR(OC) m = (∆VTR/∆IL) = 10kΩ VTR , DC (V) Overview ILOOP (mA) ILIM FIGURE 4. DC FEED CHARACTERISTIC The point on the y-axis labeled VTR(OC) is the open circuit Tip to Ring voltage and is defined by the feed battery voltage. (EQ. 18) V TR ( OC ) = V BL – 8 Feed Architecture The design implements a voltage feed current sense architecture. The device controls the voltage across Tip and Ring based on the sensing of load current. Resistors are placed in series with Tip and Ring outputs to provide the current sensing. The diagram below illustrates the concept. RB RA VIN RCS - VOUT The curve of Figure 5 determines the actual loop current for a given set of loop conditions. The loop conditions are determined by the low battery voltage and the DC loop impedance. The DC loop impedance is the sum of the protection resistance, copper resistance (ohms/foot) and the telephone off hook DC resistance. IB ILIM + 2RP RL RC - + KS FIGURE 3. VOLTAGE FEED CURRENT SENSE DIAGRAM By monitoring the current at the amplifier output, a negative feedback mechanism sets the output voltage for a defined load. The amplifier gains are set by resistor ratios (RA , RB , RC) providing all the performance benefits of matched resistors. The internal sense resistor, RCS , is much smaller than the gain resistors and is typically 20Ω for this device. The feedback mechanism, KS , represents the amplifier configuration providing the negative feedback. DC Loop Feed The feedback mechanism for monitoring the DC portion of the loop current is the loop detector. A low pass filter is used in the feedback to block voice band signals from interfering with the loop current limit function. The pole of the low pass 4-86 IA ISC ILOOP (mA) Loop supervision is provided by the switch hook detector at the DET output. When DET goes low, the low battery should be selected for DC loop feed and voice transmission. RLOOP (Ω) RKNEE FIGURE 5. ILOOP VERSUS RLOOP LOAD CHARACTERISTIC The slope of the feed characteristic and the battery voltage define the maximum loop current on the shortest possible loop as the short circuit current ISC. V TR ( OC ) – 2R P I LIM I SC = I LIM + -----------------------------------------------------10e3 (EQ. 19) The term ILIM is the programmed current limit, 1760/RIL. The line segment IA represents the constant current region of the loop current limit function. V TR ( OC ) – R LOOP I LIM I A = I LIM + -------------------------------------------------------------10e3 (EQ. 20) The maximum loop impedance for a programmed loop current is defined as RKNEE . V TR ( OC ) R KNEE = -----------------------I LIM (EQ. 21) HC5549 When RKNEE is exceeded, the device will transition from constant current feed to constant voltage, resistive feed. The line segment IB represents the resistive feed portion of the load characteristic. V TR ( OC ) I B = -----------------------R LOOP (EQ. 22) The AC feed back loop produces an echo at the VTX output of the signal injected at VRX . The echo must be cancelled to maintain voice quality. Most applications will use a summing amplifier in the CODEC front end as shown below to cancel the echo signal. R Voice Transmission VRX R - + TA RS TX IN - TIP - RB +2.4V -IN HC5518x VRX 20 VTX R R RX OUT RF 1:1 + The feedback mechanism for monitoring the AC portion of the loop current consists of two amplifiers, the sense amplifier (SA) and the transmit amplifier (TA). The AC feedback signal is used for impedance synthesis. A detailed model of the AC feed back loop is provided below. RA CODEC FIGURE 7. TRANSHYBRID BALANCE INTERFACE R + 1:1 20 RING VTX + - TA - + RS R 3R -IN 0.75R 3R 3R 3R 8K - + CFB VFB VSA R/2 FIGURE 6. AC SIGNAL TRANSMISSION MODEL The gain of the transmit amplifier, set by RS , determines the programmed impedance of the device. The capacitor CFB blocks the DC component of the loop current. The ground symbols in the model represent AC grounds, not actual DC potentials. The sense amp output voltage, VSA , as a function of Tip and Ring voltage and load is calculated using Equation 23. 10 V SA = – ( V T – V R ) -----ZL (EQ. 23) The resistor ratio, RF /RB , provides the final adjustment for the transmit gain, GTX . The transmit gain is calculated using Equation 25. R F G TX = – G 24 -------- R B Most applications set RF = RB , hence the device 2-wire to 4-wire equals the transmit gain. Typically RB is greater than 20kΩ to prevent loading of the device transmit output. The resistor ratio, RF /RA , is determined by the transhybrid gain of the device, G44 . RF is previously defined by the transmit gain requirement and RA is calculated using Equation 26. RB R A = ---------G 44 RS V VTX = – V SA ---------- 8e3 (EQ. 24) Once the impedance matching components have been selected using the design equations, the above equations provide additional insight as to the expected AC node voltages for a specific Tip and Ring load. Transhybrid Balance The final step in completing the impedance synthesis design is calculating the necessary gains for transhybrid balance. 4-87 (EQ. 26) Power Dissipation The power dissipated by the device during on hook transmission is strictly a function of the quiescent currents for each supply voltage during Forward Active operation. + V BL × I BLQ + V CC × I CCQ P FAQ = V BH × I BHQ The transmit amplifier provides the programmable gain required for impedance synthesis. In addition, the output of this amplifier interfaces to the CODEC transmit input. The output voltage is calculated using Equation 24. (EQ. 25) (EQ. 27) Off hook power dissipation is increased above the quiescent power dissipation by the DC load. If the loop length is less than or equal to RKNEE , the device is providing constant current, IA , and the power dissipation is calculated using Equation 28. P FA ( IA ) = P FA ( Q ) + ( V BL xI A ) – ( R LOOP xI 2 A ) (EQ. 28) If the loop length is greater than RKNEE , the device is operating in the constant voltage, resistive feed region. The power dissipated in this region is calculated using Equation 29. P FA ( IB ) = P FA ( Q ) + ( V BL xI B ) – ( R LOOP xI 2 B ) (EQ. 29) HC5549 Since the current relationships are different for constant current versus constant voltage, the region of device operation is critical to valid power dissipation calculations. Reverse Active POL pin and minimal voltage excursion ±0.75V, are well suited to polarized capacitors. Power Dissipation The power dissipation equations for forward active operation also apply to the reverse active mode. Overview The reverse active mode (RA, 011) provides the same functionality as the forward active mode. On hook transmission, DC loop feed and voice transmission are supported. Loop supervision is provided by either the switch hook detector (E0 = 1) or the ground key detector (E0 = 0). The device may be operated from either high or low battery. During reverse active the Tip and Ring DC voltage characteristics exchange roles. That is, Ring is typically 4V below ground and Tip is typically 4V more positive than battery. Otherwise, all feed and voice transmission characteristics are identical to forward active. Silent Polarity Reversal Changing from forward active to reverse active or vice versa is referred to as polarity reversal. Many applications require slew rate control of the polarity reversal event. Requirements range from minimizing cross talk to protocol signalling. The device uses an external low voltage capacitor, CPOL , to set the reversal time. Once programmed, the reversal time will remain nearly constant over various load conditions. In addition, the reversal timing capacitor is isolated from the AC loop, therefore loop stability is not impacted. The internal circuitry used to set the polarity reversal time is shown below. POL CPOL I2 FIGURE 8. REVERSAL TIMING CONTROL During forward active, the current from source I1 charges the external timing capacitor CPOL and the switch is open. The internal resistor provides a clamping function for voltages on the POL node. During reverse active, the switch closes and I2 (roughly twice I1) pulls current from I1 and the timing capacitor. The current at the POL node provides the drive to a differential pair which controls the reversal time of the Tip and Ring DC voltages. ∆time C POL = ---------------75000 (EQ. 30) Where ∆time is the required reversal time. Polarized capacitors may be used for CPOL . The low voltage at the 4-88 Overview The ringing mode (RNG, 100) provides the low side return path for externally supplied battery backed ringing. The ringing signal must be injected through a relay at the ring terminal. The device should be operated from the low battery voltage during this mode to minimize the overall power dissipation during ringing. Current flowing through the Tip terminal will provide the necessary ring trip information. Ringing Bias Input The ringing bias input, VRB, is a high impedance input. The VRB input is only selected during the ringing mode. The gain from the VRB input to the Tip output is typically 40V/V. The following equation shows the relationship of the Tip output voltage to the VRB input voltage. VBL V TIP = ------------ + 40 × VRB 2 (EQ. 31) A positive DC voltage at VRB is required to shift the Tip output voltage towards ground to provide the low side ringing return path. Tying the logic input F2 to VRB provides the positive voltage to offset Tip during ringing. A voltage divider is suggested to provide control the actual voltage applied to VRB. Logic Control Ringing patterns consist of silent intervals. The ringing to silent pattern is called the ringing cadence. During the silent portion of ringing, the device can be programmed to any other operating mode. The most likely candidates are low power standby or forward active. Depending on system requirements, the low or high battery may be selected. I1 75kΩ Ringing Loop supervision is provided with the ring trip detector. The ring trip detector senses the change in loop current when the phone is taken off hook. The loop detector full wave rectifies the ringing current, which is then filtered with external components RRT and CRT. The resistor RRT sets the trip threshold and the capacitor CRT sets the trip response time. Most applications will require a trip response time less than 150 milliseconds. Three very distinct actions occur when the devices detects a ring trip. First, the DET output is latched low. The latching mechanism eliminates the need for software filtering of the detector output. The latch is cleared when the operating mode is changed externally. Second, the VRS input is disabled, removing the Tip biasing signal from the line. Third, the device is internally forced to the forward active mode. HC5549 Power Dissipation Functionality The power dissipation during ringing is dictated by the load driving requirements and the ringing waveform. The key to valid power calculations is the correct definition of average and rms currents. The average current defines the high battery supply current. The rms current defines the load current. During power denial, both the Tip and Ring amplifiers are disabled, representing high impedances. The voltages at both outputs are near ground. The cadence provides a time averaging reduction in the peak power. The total power dissipation consists of ringing power, Pr , and the silent interval power, Ps. tr ts P RNG = P r ⋅ -------------- + P s ⋅ -------------tr + ts tr + ts (EQ. 32) The terms, tr and ts, represent the cadence. The ringing interval is tr and the silent interval is ts. The typical cadence ratio tr:ts is 1:2. The quiescent power of the device in the ringing mode is defined in Equation 34. P r ( Q ) = VBH ⋅ IBH Q + VBL ⋅ IBL Q + VCC ⋅ ICC Q (EQ. 33) During ringing, the device is operated from the low battery, therefore the VBH power contribution is negligible. The total power during the ringing interval is the sum of the quiescent power and loading power: 2 V rms P r = P r ( Q ) + VBL ⋅ I AVG – -----------------------------------------Z +R REN (EQ. 34) LOOP For sinusoidal waveforms, the average current, IAVG, is defined in equation 36. V rms ⋅ 2 2 I AVG = --- ----------------------------------------- π Z +R REN (EQ. 35) LOOP The only amplifier providing load current during ringing is the Tip amplifier. Therefore the total power contribution from the device is half the average power required by the load. V rms ⋅ 2 1 I AVG = --- ----------------------------------------- π Z +R REN (EQ. 36) LOOP The silent interval power dissipation will be determined by the quiescent power of the selected operating mode. Power Denial Overview The power denial mode (111) will shutdown the entire device except for the logic interface. Loop supervision is not provided. This mode may be used as a sleep mode or to shutdown in the presence of a persistent thermal alarm. Switching between high and low battery will have no effect during power denial. 4-89 Thermal Shutdown In the event the safe die temperature is exceeded, the ALM output will go low and DET will go high and the part will automatically shut down. When the device cools, ALM will go high and DET will reflect the loop status. If the thermal fault persists, ALM will go low again and the part will shutdown. Programming power denial will permanently shutdown the device and stop the self cooling cycling. Battery Switching Overview The integrated battery switch selects between the high battery (VBH) and low battery (VBL). The battery switch is controlled with the logic input BSEL. When BSEL is a logic high, the high battery is selected and when a logic low, the low battery is selected. All operating modes of the device will operate from high or low battery except forward loop back. Functionality The logic control is independent of the operating mode decode. Independent logic control provides the most flexibility and will support all application configurations. When changing device operating states, battery switching should occur simultaneously with or prior to changing the operating mode. In most cases, this will minimize overall power dissipation and prevent glitches on the DET output. The only external component required to support the battery switch is a diode in series with the VBH supply lead. In the event that high battery is removed, the diode allows the device to transition to low battery operation. Low Battery Operation All off hook operating conditions and ringing should use the low battery. The prime benefit will be reduced power dissipation. The typical low battery for the device is -24V. However this may be increased to support longer loop lengths or high loop current requirements. Standby conditions may also operate from the low battery if MTU compliance is not required, further reducing standby power dissipation. High Battery Operation The high battery should be used for standby conditions which must provide MTU compliance. During standby operation the power consumption is typically 40 mW with 48V battery. If standby requirements do not require high battery operation, then a lower battery will result in lower standby power. HC5549 Uncommitted Switch snubber diode is not required when using the uncommitted switch as a relay driver. Overview The uncommitted switch is a three terminal device designed for flexibility. The independent logic control input, SWC, allows switch operation regardless of device operating mode. The switch is activated by a logic low. The positive and negative terminals of the device are labeled SW+ and SW- respectively. Relay Driver Test Load The switch may be used to connect test loads across Tip and Ring. The test loads can provide external test termination for the device. Proper connection of the uncommitted switch to Tip and Ring is shown below. TIP The uncommitted switch may be used as a relay driver by connecting SW+ to the relay coil and SW- to ground. The switch is designed to have a maximum on voltage of 0.6V with a load current of 45mA. RING TEST LOAD +5V SW+ RELAY SWSW+ SW- FIGURE 10. TEST LOAD SWITCHING SWC FIGURE 9. EXTERNAL RELAY SWITCHING Since the device provides the ringing waveform, the relay functions which may be supported include subscriber disconnect, test access or line interface bypass. An external 4-90 SWC The diode in series with the test load blocks current from flowing through the uncommitted switch when the polarity of the Tip and Ring terminals are reversed. In addition to the reverse active state, the polarity of Tip and Ring are reversed for half of the ringing cycle. With independent logic control and the blocking diode, the uncommitted switch may be continuously connected to the Tip and Ring terminals. HC5549 Basic Application Circuit CPS1 CPS2 D1 CPS3 VCC RP1 VBL VBH CRX TIP VRX U1 PROTECTION NETWORK VRB HC5549 RP2 RB1 RB2 CTX RING VTX RS SW+ -IN SW- CFB CRT VFB -48V RRT RTD SWC RSH RD BSEL E0 RIL ILIM F0 F1 CDC VCC CDC F2 CPOL DET POL ALM CIL AGND BGND FIGURE 11. HC5549 BASIC APPLICATION CIRCUIT Basic Application Circuit Component List COMPONENT VALUE TOLERANCE RATING U1 HC5549 N/A N/A RRT 20kΩ 1% RSH 49.9kΩ RIL RS COMPONENT VALUE TOLERANCE RATING n/a n/a n/a n/a 0.1W CDC 4.7µF 20% 10V 1% 0.1W CPS1 0.1µF 20% >100V 71.5kΩ 1% 0.1W CPS2, CPS3 0.1µF 20% 100V 210kΩ 1% 0.1W D1 1N400X type with breakdown > 100V. CRX, CRS, CTX, CRT, 0.47µF CPOL, CFB 20% 10V RP1, RP2 Protection resistor values are application dependent and will be determined by protection requirements. Standard applications will use ≥ 35Ω per side. Design Parameters: Ring Trip Threshold = 90 mA peak., Switch Hook Threshold = 12 mA, Loop Current Limit = 24.6 mA, Synthesize Device Impedance = 210kΩ/400= 525Ω, with 39Ω protection resistors, impedance across Tip and Ring terminals = 603Ω. 4-91 HC5549 Pin Description PLCC SYMBOL DESCRIPTION 1 TIP 2 BGND 3 VBL Low battery supply connection. 4 VBH High battery supply connection. 5 SW+ Uncommitted switch positive terminal. 6 SW- Uncommitted switch negative terminal. 7 SWC Switch control input. This TTL compatible input controls the uncommitted switch, with a logic “0” enabling the switch and logic “1” disabling the switch. 8 F2 Mode control input - MSB. F2-F0 for the TTL compatible parallel control interface for controlling the various modes of operation of the device. 9 F1 Mode control input. 10 F0 Mode control input. 11 E0 Detector Output Selection Input. This TTL input controls the multiplexing of the SHD (E0=1) and GKD (E0 =0) comparator outputs to the DET output based upon the state at the F2-F0 pins. 12 DET Detector Output - This TTL output provides hook status of the loop based upon the selected operating mode. The detected output will either be switch hook, ground key or ring trip. 13 ALM Thermal Shutdown Alarm. This pin signals the internal die temperature has exceeded safe operating temperature and the device has been powered down automatically. 14 AGND Analog ground reference. This pin should be externally connected to BGND. 15 BSEL Selects between high and low battery, with a logic “1” selecting the high battery and logic “0” the low battery. 16 NC This pin is a “no connect” and should remain floating proper device operation. 17 POL Capacitor connected to this pin sets the polarity reversal slew rate. 18 VRB Ringing Bias Input - Analog input to offset Tip output towards ground while in Ringing Mode. 19 VRX Analog Receive Voltage - 4-wire analog audio input voltage. AC couples to codec. 20 VTX Transmit output voltage - Output of impedance matching amplifier, AC couples to codec. 21 VFB Feedback voltage for impedance matching. This voltage is scaled to accomplish impedance matching. 22 -IN 23 VCC Positive voltage power supply. 24 CDC DC Biasing Filter Capacitor - Connects between this pin and VCC. 25 RTD Ring trip filter network. 26 ILIM Loop Current Limit programming resistor. 27 RD Switch hook detection threshold programming resistor. 28 RING TIP power amplifier output. Battery Ground - To be connected to zero potential. All loop current and longitudinal current flow from this ground. Internally separate from AGND but it is recommended that it is connected to the same potential as AGND. Impedance matching amplifier summing node. RING power amplifier output. 4-92