XRT5894 Four-Channel E1 Line Interface (3.3V or 5.0V) March 2000-3 FEATURES D Compliant with ITU G.703 Pulse Mask Template for 2.048Mbps (E1) Rates D Four Independent CEPT Transceivers D Logical Inputs Accept either 3.3V or 5.0V Levels D Ultra-Low Power Dissipation D +3.3V or 5.0V Supply Operations D Supports Differential Transformer Coupled Receivers and Transmitters D On Chip Pulse Shaping for Both 75W and 120W Line Drivers D Compliant with ITU G.775 LOS Declaration/Clearing Recommendation D Optional User Selectable LOS Declaration/Clearing Delay D Individual Transmit Channel Over Temperature Protection APPLICATIONS D SDH Multiplexer D Digital Cross Connects GENERAL DESCRIPTION The XRT5894 is an optimized four channel 3.3V line interface unit fabricated using low power CMOS technology. The device contains four independent E1 channels. Each channel performs the driver and receiver functions necessary to convert bipolar signals to logical levels and vice versa. The device requires transformers on both receiver and transmitter sides, and supports both balanced and unbalanced interfaces. The device offers two distinct modes of LOS detection. The first method, which does not require an external clock, provides an LOS output indication signal with thresholds and delay that comply with the ITU G.775 requirements. In the second mode, the user provides an external clock that increases the delay for LOS declaration and clearing. This feature provides the user with the flexibility to implement LOS specifications that require a delay greater than the G.775 requirements. ORDERING INFORMATION Part No. Package Operating Temperature Range XRT5894IV 64 Lead TQFP (10 x 10 x 1.4mm) -40°C to +85°C Rev. 1.10 E2000 EXAR Corporation, 48720 Kato Road, Fremont, CA 94538 z (510) 668-7000 z FAX (510) 668-7017 XRT5894 BLOCK DIAGRAM Transceiver 1 Transceiver 2 Transceiver 3 Tranceiver 4 RTIP4 (43) RX Input TIP 1:2 RXPOS4 (47) R1 RING R2 Signal Peak Detector RRING4 (42) Receive Comparators RXNEG4 (46) VCC LOS Detect LOSCNT (45) Loss Delay Counter 1 Mux O LOS4 (48) LOSSEL (25) Transmit Line Drivers TIP TX OUTPUT RING 2:1 R3 TTIP4 (53) 9.1 R4 Duty Cycle Adjust Pulse Shaping TRING4 (55) 9.1 0 0 Mux NRZ To RZ TXCLK4 (51) TXPOS4 (49) TXNEG4 (50) 1 1 Figure 1. XRT5894 Block Diagram Receiver Notes D The same type 1:2CT ratio transformer may be used at the receiver input and transmitter output. D LOSCNT (pin 45) is unconnected when LOSSEL is logic 1, or connected to an external clock when LOSSEL is logic 0. D R1 and R2 are both 150W for 75W operation, or 240W for 120W operation. Transmitter Notes D Return loss exceeds ITU G.703 specification with these resistors and a 1:2CT ratio input transformer. D Return loss exceeds ETSI 300 166 specification with a 1:2 ratio transformer. LOS (Loss of Signal) Notes D R3 and R4 are always 9.1W for both 75W and 120W applications. D LOSSEL (pin 25) is connected to logic “1” for ITU G.775 compliant LOS delay, or to logic 0 for user programmable additional delay. Rev. 1.10 2 XRT5894 LOS4 RXPOS4 RXNEG4 LOSCNT GND RTIP4 RRING4 GND VCC GND TRING3 VCC TTIP3 GND RTIP3 RRING3 PIN CONFIGURATION 48 49 32 64 17 GND TRING2 VCC GND VCC 16 RTIP1 RRING1 VCC LOS1 RXPOS1 RXNEG1 VCC 1 TTIP2 GND RTIP2 RRING2 TXPOS4 TXNEG4 TXCLK4 GND TTIP4 VCC TRING4 GND GND TRING1 VCC TTIP1 GND TXCLK1 TXNEG1 TXPOS1 33 64 LEAD THIN QUAD FLAT PACK (10 x 10 x 1.4 mm, TQFP) Rev. 1.10 3 TXCLK3 TXNEG3 TXPOS3 LOS3 RXPOS3 RXNEG3 GND LOSSEL NC VCC RXNEG2 RXPOS2 LOS2 TXPOS2 TXNEG2 TXCLK2 XRT5894 PIN DESCRIPTION Pin # Symbol Type Description 1 LOS1 O Receiver 1 Loss of Signal. Asserted during LOS condition. 2 RXPOS1 O Receiver 1 Positive Data Out. Positive RZ data output for channel 1. 3 RXNEG1 O Receiver 1 Negative Data Out. Negative RZ data output for channel 1. 4 VCC 5 RTIP1 I Receiver 1 Positive Bipolar Input. 6 RRING1 I Receiver 1 Negative Bipolar Input. 7 VCC Positive Supply (+3.3V or +5.0V + 5%). Analog circuitry. 8 GND Analog Ground. 9 VCC Positive Supply. (+3.3V or +5.0V + 5%). Analog circuitry. 10 GND Analog Ground. 11 TRING2 12 VCC 13 TTIP2 Positive Supply (+3.3V or +5.0V + 5%). Digital circuitry. O Transmitter 2 Negative Bipolar Output. Positive Supply (+3.3V or +5.0V + 5%). Transmitter channel 2. O Transmitter 2 Positive Bipolar Output. 14 GND 15 RTIP2 I Analog Ground. Transmitter channel 2. Receiver 2 Positive Bipolar Input. 16 RRING2 I Receiver 2 Negative Bipolar Input. 17 TXCLK2 I Transmitter 2 Clock Input. Use for clocked mode with NRZ data.1 18 TXNEG2 I Transmitter 2 Negative Data Input. Negative NRZ or RZ data input.1 19 TXPOS2 I Transmitter 2 Positive Data Input. Positive NRZ or RZ data input.1 20 LOS2 O Receiver 2 Loss of Signal. Asserted during LOS condition. 21 RXPOS2 O Receiver 2 Positive Data Out. Positive RZ data output for channel 2. 22 RXNEG2 O Receiver 2 Negative Data Out. Negative RZ data output for channel 2. 23 VCC Positive Supply (+3.3V or +5.0V + 5%). Digital circuitry. 24 NC No Connect. 25 LOSSEL 26 GND 27 RXNEG3 O Receiver 3 Negative Data Out. Negative RZ data output for channel 3. 28 RXPOS3 O Receiver 3 Positive Data Out. Positive RZ data output for channel 3. 29 LOS3 O Receiver 3 Loss of Signal. Asserted during LOS condition. 30 TXPOS3 I Transmitter 3 Positive Data Input. Positive NRZ or RZ data input.1 31 TXNEG3 I Transmitter 3 Negative Data Input. Negative NRZ or RZ data input.1 32 TXCLK3 I Transmitter 3 Clock Input. Use for clocked mode with NRZ data.1 33 RRING3 I Receiver 3 Negative Bipolar Input. 34 RTIP3 I Receiver 3 Positive Bipolar Input. I Loss of Signal Delay Select. “Hi” selects G.775, “Lo” selects user programmable.1 Digital Ground. Note: 1 Has internal pull-up 50KW resistor. Rev. 1.10 4 XRT5894 PIN DESCRIPTION (CONT’D) Pin # Symbol Type Description 35 GND 36 TTIP3 37 VCC 38 TRING3 39 GND Analog Ground. Transmitter channel 3. 40 VCC Positive Supply (+3.3V or +5.0V + 5%). Analog circuitry. 41 GND Analog Ground. 42 RRING4 I Receiver 4 Negative Bipolar Input. 43 RTIP4 I Receiver 4 Positive Bipolar Input. 44 GND 45 LOSCNT I Loss of Signal Timing Clock Input. For user--programmable LOS delay.1 46 RXNEG4 O Receiver 4 Negative Data Out. Negative RZ data output for channel 4. 47 RXPOS4 O Receiver 4 Positive Data Out. Positive RZ data output for channel 4. 48 LOS4 O Receiver 4 Loss of Signal. Asserted during LOS condition. 49 TXPOS4 I Transmitter 4 Positive Data Input. Positive NRZ or RZ data input.1 50 TXNEG4 I Transmitter 4 Negative Data Input. Negative NRZ or RZ data input.1 51 TXCLK4 I Transmitter 4 Clock Input. Use for clocked mode with NRZ data.1 Analog Ground. O Transmitter 3 Positive Bipolar Output. Positive Supply (+3.3V or +5.0V + 5%). Transmitter channel 3. O Transmitter 3 Negative Bipolar Output. Analog Ground. 52 GND 53 TTIP4 Analog Ground. Transmitter channel 4. 54 VCC 55 TRING4 56 GND Digital Ground. 57 GND Analog Ground. 58 TRING1 O Transmitter 4 Positive Bipolar Output. Positive Supply (+3.3V or +5.0V + 5%). Transmitter channel 4. O O Transmitter 4 Negative Bipolar Output. Transmitter 1 Negative Bipolar Output. 59 VCC 60 TTIP1 Positive Supply (+3.3V or +5.0V + 5%). Transmitter channel 1. 61 GND 62 TXCLK1 I Transmitter 1 Clock Input. Use for clocked mode with NRZ data.1 63 TXNEG1 I Transmitter 1 Negative Data Input. Negative NRZ or RZ data input.1 64 TXPOS1 I Transmitter 1 Positive Data Input. Positive NRZ or RZ data input.1 O Transmitter 1 Positive Bipolar Output. Analog Ground. Transmitter channel 1. Note: 1 Has internal pull-up 50KW resistor. Rev. 1.10 5 XRT5894 ELECTRICAL CHARACTERISTICS Test Conditions: VCC = 3.3V or 5.0V + 5%, TA = -40 to 25 to 85°C, Unless Otherwise Specified Symbol Parameter Min. Typ. Max. Unit Conditions DC Electrical Characteristics Parameters VCC Voltage Supply 3.135 3.3 3.465 V 3.3V Operation VCC Voltage Supply 4.75 5.0 5.25 V 5V Operation VIH Input High Level 2.0 5.0 V VIL Input Low Level 0.8 V Inputs Outputs VOH Output High Level VOL Output Low Level 2.4 V IOH = -4mA 0.4 V IOL = 4mA 12 dB Cable loss at 1.024MHz (Relative to 0dB = 2.37Vp measured from RTIP or RRING to ground). dB With 6dB cable loss Receiver Specifications RXCL Allowable Cable Loss 0 10 RXIM Interference Margin -15 -12 RXXI Receiver Slicing Threshold 45 50 55 % % of peak input voltage at -3dB cable loss 15 32 dB Relative to 0dB = 2.37Vp Measured from RTIP or RRING to ground. dB Relative to 0dB = 2.37Vp measured from RTIP or RRING to ground. RXLOSSET LOS Must Be Set If RX Sig. Atten. ² 32dB (For Any Valid Data Pattern) RXLOSCLR LOS Must Be Cleared If RX Sig. Atten. < 9dB 9 RXLOSHYST Hysteresis on Input Data 1 dB For LOS output state change Input Impedance 5 kW Up to 3.072MHz (Measured from RTIP or RRING to ground). RXIN 12 Power Specifications VCC = 3.3V PD Power Dissipation 460 590 mW All 1’s Transmit and Receive 75W PD PC Power Dissipation 117 155 mW All Drivers Power Down Power Consumption 75W 770 900 mW All 1’s Transmit and Receive PC Power Consumption 75W 555 675 mW 50% data density, Transmit and Receive PC Power Consumption 120W 635 780 mW All 1’s Transmit and Receive PC Power Consumption 120W 475 605 mW 50% data density, Transmit and Receive Power Specifications VCC = 5.0V PD Power Dissipation 945 1240 mW All 1’s Transmit and Receive 75W PD Power Dissipation 235 290 mW All Drivers Power Down PC Power Consumption 75W 1250 1555 mW All 1’s Transmit and Receive Note: Bold face parameters are covered by production test and guaranteed over operating temperature range. Rev. 1.10 6 XRT5894 ELECTRICAL CHARACTERISTICS (CONT’D) Test Conditions: VCC = 3.3V or 5.0V + 5%, TA = -40 to 25 to 85°C, Unless Otherwise Specified Symbol Parameter Min. Typ. Max. Unit Conditions Power Specifications VCC =5.0V (Cont’d) PC Power Consumption 120W 1075 1345 mW All 1’s Transmit and Receive PC Power Consumption 75W 1025 1300 mW 50% data density, Transmit and Receive PC Power Consumption 120W 940 1220 mW 50% data density, Transmit and Receive AC Electrical Characteristics VTXOUT Output Pulse Amplitude (RL = 75W) 2.13 2.37 2.60 V Trans. = 1:2 ratio, 9.1W in series with each end of primary VTXOUT Output Pulse Amplitude (RL = 120W) 2.70 3.0 3.30 V Trans. = 1:2 ratio, 9.1W in series with each end of primary TXPW Output Pulse Width 224 244 264 ns PNIMP Pos/Neg Pulse Unbalanced 5 % 488 ns T1 TXCLK Clock Period (E1) T2 TXCLK Duty Cycle 30 TSU Data Set-up Time, TDATA to TXCLK 75 ns 50% TXCLK Duty Cycle THO Data Hold Time, TDATA to TXCLK 30 ns 50% TXCLK Duty Cycle 50 70 % TR TXCLK Rise Time (10% to 90%) 40 ns TF TXCLK Fall Time (10% to 90%) 40 ns Data Prop. Delay No-Clock Mode 35 Data Prop. Delay Clock Mode 470 T3-noclk T3-clk 50 ns 50% TXCLK Duty Cycle T4 Receive Data High 269 ns 0dB Cable Loss T5 RX Data Prop. Delay 40 ns 15pF Load T6 Receive Rise Time 40 ns 15pF Load T7 Receive Rise Time 40 ns 15pF Load 219 244 ns Note: Bold face parameters are covered by production test and guaranteed over operating temperature range. ABSOLUTE MAXIMUM RATINGS Storage Temperature . . . . . . . . . . . . -65°C to +150°C Operating Temperature . . . . . . . . . . -40°C to +85°C Supply Voltage . . . . . . . . . . . . . . . . . . . -0.3V to +6.0V ESD Protection . . . . . . . . . . . . . . . . . . >1000V (HBM) Rev. 1.10 7 XRT5894 Disabling Output Drivers Output drivers may be individually disabled (hi-z output) by either of the following methods. 1. Either connect the transmit data inputs TXPOS and TXNEG for the channel to be disabled to a logic 1 source (VCC), or allow them to float (inputs have internal pull--up resistors). 2. Connect TXCLK for the channel to be disabled to logic 0 source (Ground), and also apply data to the TXPOS and TXNEG inputs of that channel. TRANSFORMER REQUIREMENTS Turns Ratio Line Impedance Turns Ratio Line Impedance 1:2 CT 75W or 120W 1:2 75W or 120W Table 1. Input Transformer Requirements Table 2. Output Transformer Requirements Note: The same type 1:2 CT ratio device may be used at both receiver input and transmitter output. The following transformers have been tested with the XRT5894: HALO type TG26-1205(package contains two 1 CT:2 CT ratio transformers) Pulse type PE-65535 (1:2 CT ratio) Transpower Technologies type TTI 7154-R (1:2 CT ratio) Magnetic Supplier Information: HALO Electronics, Inc. P.O. Box 5826 Redwood City, CA 94063 Tel. (415) 568-5800 Fax. (415)568-6161 Pulse Telecom Product Group P.O. Box 12235 San Diego, CA 92112 Tel. (619) 674-8100 Fax. (619) 674-8262 Transpower Technologies, Inc. 24 Highway 28, Suite 202 Crystal Bay, NV 89402--0187 Tel. (702) 831--0140 Fax. (702) 831--3521 Rev. 1.10 8 XRT5894 TSU THO TXPOS (n) TSU TXNEG (n) T2 T1 TR TXCLK (n) THO TF TXPW T3 T3 VTXOUT TXOUT (n) VTXOUT TXPW Figure 2. Transmit Timing Diagram RXIN (n) T5 T4 T6 T7 RPOS (n) T5 T4 RXNEG (n) Figure 3. Receive Timing Diagram Rev. 1.10 9 T6 T7 XRT5894 RETURN LOSS SPECIFICATIONS The following transmitter and receiver return loss specifications are based on a typical 1:2CT ratio transformer. 75W 120W Frequency Range Min. Typ. Min. Typ. Unit 51kHz to 102kHz 16 22 10 15 dB 102kHz to 2.048MHz 16 22 10 15 dB 2.048MHz to 3.072MHz 11 18 10 14 dB Table 3. Transmitter Return Loss Specification Transmit Return Loss Notes D Output transformer ratio is 1:2 (return loss exceeds ETSI 300 166 with this transformer). D For both 75W and 120W applications, 9.1W, 1% resistors are connected between each end of the transformer primary and the XRT5894 TTIP and TRING pins. 75W 120W Frequency Range Min. Typ. Min. Typ. Unit 51kHz to 102kHz 16 28 15 18 dB 102kHz to 2.048MHz 22 34 22 25 dB 2.048MHz to 3.072MHz 18 26 20 30 dB Table 4. Receiver Return Loss Specification Receiver Return Loss Notes D Input transformer ratio is 1:2 CT. D Each half of transformer secondary is terminated with 150W for 75W operation, or 240W for 120W operation (resistors are 1% tolerance). D Transformer center tap is grounded. Rev. 1.10 10 XRT5894 SYSTEM DESCRIPTION This device is a four channel E1 transceiver that provides an electrical interface for 2.048Mbps applications. Its unique architecture includes four receiver circuits that convert ITU G.703 compliant bipolar signals to TTL compatible logic levels. Each receiver includes a LOS (Loss of Signal) detection circuit that may be configured for either a fixed or a user-programmable LOS response time delay. Similarly, in the transmit direction, four transmitters convert TTL compatible logic levels to G.703 compatible bipolar signals. Each transmitter may be operated either with RZ, or NRZ data types. In NRZ mode a transmit clock is required as well. The following description applies to any of the four receivers or transmitters contained in the XRT5894. Therefore, the suffix numbers for a particular channel are deleted for simplicity. i.e. “RTIP” applies to RTIP1 through RTIP4. specified in the ITU G.775. This is done by providing a user-supplied clock to LOSCNT (pin 45). The “user programmable mode” is provisioned to allow systems designers to comply with older versions of LOS specifications in legacy systems. It needs to be stressed that the delay for declaration and clearing of the LOS condition will never be less than the range specified in the G.775 specification (10-255 pulse intervals). The LOS detection/clearing circuitry of the XRT5894 in “automatic” mode will detect LOS when the incoming signal has “no transitions” i.e. when the signal level is less than or equal to a signal level AD dB below nominal signal level, for N consecutive pulse intervals, where 10<N<255. The value of AD can vary between 10dB to 32dB depending on the ones density of the incoming signal assuming the received data has minimum permissible ones density. Furthermore LOS detect is cleared when the incoming signal has “transitions,” i.e. when the signal level is greater than or equal to a signal level of AC dB below nominal, for N consecutive pulse intervals, where 10<N<255. The value of AC can vary between 9dB to 31dB depending on the ones density of the incoming signal assuming the received data has minimum permissible ones density. Each pulse interval is 488ns at E1 rates. The absolute value of AC is always smaller than AD by at least 1dB. Receiver Operation A bipolar signal is transformer-coupled to the receiver differential inputs (RTIP and RRING). The receiver is able to tolerate up to 12dB of line loss measured at 1.024MHz. It contains slicing circuitry that automatically samples the incoming data at a fixed percentage (50% nominal) of the peak signal amplitude. A precision peak detector maintains the slicing level accuracy. The TTL compatible receiver output data rails appear at the RXPOS and RXNEG pins. The pulse width of this data; which is in RZ format, is a function of the amount of the cable loss present. The LOS detection/clearing criteria described above is fully compliant with G.775 LOS specification. In the “user programmable” mode the user has the option of extending the declaration and clearing delay (10<N<255) by an amount which is equal to 2048 x T. T is the time period of the clock supplied to LOSCNT (pin 45) by the user. Receiver Loss Of Signal Detection (LOS) Absence of signal at any receiver input is detected by the loss of signal (LOS) circuit. One LOS detection circuitry is provisioned for each receiver. The LOS signal is asserted (LOS=1) when a LOS condition is detected and is cleared (LOS=0) when a valid input signal is restored. Nominal signal level is defined as 2.37V peak measured between RTIP or RRING and ground. (This voltage will be present in 75W applications using a 1:2 CT ratio input transformer terminated in 300W with the center tap grounded with 0dB of cable and a 2.37V peak amplitude transmit pulse at the cable input.) Two modes of LOS circuit operation are supported. These distinct modes are called “automatic” and “user-programmable”. When LOSSEL (pin 25) is set to logic “1”, the automatic mode is selected. In this mode the LOS condition will be declared and cleared in full compliance with ITU G.775 specification. When LOSSEL is connected to logic “0”, the user-programmable delay mode is enabled. In this mode the user has the option of extending the delay of LOS declaration and clearing Transmitters This device contains four identical ITU G.703 compliant transmitters. The output stage of each transmitter is a differential voltage driver. External resistors need to be connected to the primary of output transformer. This is necessary to maintain an accurate source impedance Rev. 1.10 11 XRT5894 that ensures compliance to ETSI 300 166 return loss requirement. present at this pin, the transmitter detects its presence and operates in the clocked mode. In this mode, the transmit input should be supplied with full-width NRZ pulses. If a clock is not present at the TXCLK input (pin is left open), the part operates in the clockless mode. In this mode, RZ data should be supplied to the device. Each transmit channel of XRT5894 has a duty cycle correction circuitry. This enables the device to produce output bipolar pulses fully compliant with G.703 despite having TXCLK signal with 30% to 70% duty cycle. TTL compatible dual rail transmit data signals are supplied to TXPOS and TXNEG inputs. The transmitter differential outputs TTIP and TRING are connected to the output transformer primary through series 9.1W resistors. All the four transmitters can be operated in two distinct modes of operation referred to as “clocked” or “clockless” modes. The operational mode is selected automatically based on the signal provided to TXCLK input. If a clock is 269 ns (244 + 25) Nominal pulse 20% V = 100% 10% 194 ns (244 -- 50) 10% 20% 50% 244 ns 219 ns (244 -- 25) 10% 10% 0% 10% 20% 488 ns (244 + 244) Note: V corresponds to the nominal peak value Figure 4. CCITT G.703 Pulse Template Rev. 1.10 12 10% XRT5894 Transmitter Output Pulse Measurement Figure 5 shows a typical transmit pulse plotted on the template shown in ITU G.703 Figure 15/G.703. The following conditions apply: VCC=3.30V Transmitter output transformer secondary terminated with 120W All ones signal Receiver output looped backed into transmitter digital input Operation without transmitter clock (RZ data) Measurement made with a Tektronix TDS640 digital scope set to full bandwidth 1.2 1.0 Normalized Amplitude 0.8 0.6 0.4 0.2 0 -0.2 -244 -122 0 122 Time (ns) Figure 5. XRT5894 Output Pulse Rev. 1.10 13 244 XRT5894 Transmitter Output Return Loss Measurements The following measurements were made with a Wandel and Goltermann SNA--2 Network Analyzer equipped with an RFZ--1 75W Return Loss Bridge. A 75W to 120W impedance matching transformer was used to make the 120W measurement. A network analyzer calibration run subtracted out the effects of this transformer. This configuration was used for both 75W and 120W measurements. The only change was the termination resistance provided by the return loss bridge. Test Results: Table 5 compares measured output return loss with requirements in ETSI FINAL DRAFT prETS 300 166, June 1993. These results show that measured return loss is mainly determined by the characteristics of the output transformer. This is particularly evident for the 120W load where the measured result is better than the calculated value. Test Conditions: D Output transformer ratio was 1:2. D Transmitter series resistors (R3 and R4 in Figure 1) were 9.1W . D Device was powered from a 3.3V source, transmitter was enabled, and no output data was present. Frequency (KHz) ETSI Spec. (Min. dB) Meas. Value (dB) 75W Load Meas. Value (dB) 120W Load 0.025 fb 51.2 6 22.6 15.4 0.05 fb 102.4 8 22.6 15.7 1.5 fb 3072 8 18.0 14.6 Specified Frequency Table 5. Transmitter Output Return Loss Measurements Notes: fb = 2048KHz This data shows that the XRT5894 is fully compliant with the ETSI Output Return Loss Specification for E1 operation with either 75W or 120W loads. Rev. 1.10 14 XRT5894 The following pictures show typical results of measurements that made over a 50 KHz to 3.5MHz frequency range. Figure 6. 75W Return Loss Measurement Figure 6 shows a return loss better than 20dB at low frequencies that decreases to about 12dB at 3.5MHz. Since the source and load resistances are well--matched, the return loss degradation is due to the transformer. Figure 7. 120W Return Loss Measurement Figure 7 shows that for the 120W case, transformer characteristics improve return loss at lower frequencies. At 3.5 MHz, return loss is close to the calculated 13.8dB for a 75W source terminated with 120W. Rev. 1.10 15 XRT5894 Output Transformer Selection A 1:2 ratio transformer is recommended for both 75W and 120W operation because the transmitter, when equipped with this device, meets both the ITU G.703 output pulse amplitude requirement and, the ETSI return loss specification. Although a center--tapped output transformer is not required, choosing a part with a center-tapped secondary allows the use of the same type of unit at the receiver input. A theoretical justification for the 1:2 ratio transformer follows: RSpos TTIP R3 1:n VSpos VO VSneg RL TRING RSneg R4 Figure 8. Transmitter Line Driver Model Where: Vspos = Vsneg = 1.25V typical (Differential line driver peak output voltage swing) Rspos = Rsneg = 0.8W typical (Differential line driver internal source resistance) R3 = R4 = 9.1W (Differential line driver external source resistance from Figure 1) RL = 75W or 120W (Transmitter load resistance) n = 2 (Transformer turns ratio) Vo = Transmitter peak output voltage (Measured across RL = 75W or RL = 120W ) Figure 9 may be converted to a single--ended model: RSint RSext 1:n VS VO Figure 9. Single-ended Line Driver Model Where: VS = ÷Vspos÷ + ÷Vsneg÷ RSint = RSpos + Rsneg RSext = R3 + R4 Rev. 1.10 16 RL XRT5894 This may be further simplified: RT I Vs Veq Figure 10. Equivalent Circuit Where: RT = RSint + Rsext Req = RL n2 Therefore: I = Vs RT + Req Veq = I Req Vo = n Veq And: Return Loss = 20 log RT + Req RT-- Req Table 5 contains the results of calculations made with these equations. The numbers show that output pulse amplitude is within millivolts of the nominal values of 2.37V and 3.00V specified by ITU G.703 for 75W and 120W operation. Also, the 1:2 ratio transformer provides an almost-perfect match for 75W operation, and return loss is well within the ETSI specification for the 120W load. Load Resistance RL (W) Pulse Amplitude Vo (Volts Peak) Output Return Loss (dB) 75 2.43 31.3 120 3.01 13.8 Table 5. Calculated Transmitter Pulse Amplitude and Return Loss Rev. 1.10 17 XRT5894 64 LEAD THIN QUAD FLAT PACK (10 x 10 x 1.4 mm, TQFP) Rev. 2.00 D D1 48 33 49 32 D1 64 17 1 A2 16 B e C A Seating Plane D a A1 L INCHES SYMBOL A A1 A2 B C D D1 e L a MIN MILLIMETERS MAX MIN 0.055 0.063 0.002 0.006 0.053 0.057 0.005 0.009 0.004 0.008 0.465 0.480 0.390 0.398 0.020 BSC 0.018 0.030 1.40 0.05 1.35 0.13 0.09 11.80 9.90 0° 7° MAX 1.60 0.15 1.45 0.23 0.20 12.20 10.10 0.50 BSC 0.45 0.75 0° Note: The control dimension is the millimeter column Rev. 1.10 18 7° XRT5894 NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained herein are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 2000 EXAR Corporation Datasheet March 2000 Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. Rev. 1.10 19