DP8392A/NS32492A Coaxial Transceiver Interface General Description Features The DP8392A Coaxial Transceiver Interface (CTI) is a coaxial cable line driver/receiver for Ethernet/Thin Ethernet (Cheapernet) type local area networks. The CTI is connected between the coaxial cable and the Data Terminal Equipment (DTE). In Ethernet applications the transceiver is usually mounted within a dedicated enclosure and is connected to the DTE via a transceiver cable. In Cheapernet applications, the CTI is typically located within the DTE and connects to the DTE through isolation transformers only. The CTI consists of a Receiver, Transmitter, Collision Detector, and a Jabber Timer. The Transmitter connects directly to a 50 ohm coaxial cable where it is used to drive the coax when transmitting. During transmission, a jabber timer is initiated to disable the CTI transmitter in the event of a longer than legal length data packet. Collision Detection circuitry monitors the signals on the coax to determine the presence of colliding packets and signals the DTE in the event of a collision. The CTI is part of a three chip set that implements the complete IEEE 802.3 compatible network node electronics as shown below. The other two chips are the DP8391 Serial Network Interface (SNI) and the DP8390 Network Interface Controller (NIC). The SNI provides the Manchester encoding and decoding functions; whereas the NIC handles the Media Access Protocol and the buffer management tasks. Isolation between the CTI and the SNI is an IEEE 802.3 requirement that can be easily satisfied on signal lines using a set of pulse transformers that come in a standard DIP. However, the power isolation for the CTI is done by DC-to-DC conversion through a power transformer. Y Y Y Y Y Y Y Y Y Compatible with Ethernet II, IEEE 802.3 10Base5 and 10Base2 (Cheapernet) Integrates all transceiver electronics except signal & power isolation Innovative design minimizes external component count Jabber timer function integrated on chip Externally selectable CD Heartbeat allows operation with IEEE 802.3 compatible repeaters Precision circuitry implements receive mode collision detection Squelch circuitry at all inputs rejects noise Designed for rigorous reliability requirements of IEEE 802.3 Standard Outline 16-pin DIP uses a special leadframe that significantly reduces the operating die temperature Table of Contents 1.0 2.0 3.0 3.1 3.2 3.3 3.4 4.0 5.0 6.0 7.0 8.0 9.0 10.0 System Diagram Block Diagram Functional Description Receiver and Squelch Transmitter and Squelch Collision and Heartbeat Jabber Timer Connection Diagram Pin Descriptions Absolute Maximum Ratings Electrical Characteristics Switching Characteristics Timing and Load Diagram Physical Dimensions 1.0 System Diagram TL/F/7405 – 1 IEEE 802.3 Compatible Ethernet/Cheapernet Local Area Network Chip Set C1995 National Semiconductor Corporation TL/F/7405 RRD-B30M105/Printed in U. S. A. DP8392A/NS32492A Coaxial Transceiver Interface May 1988 2.0 Block Diagram TL/F/7405 – 2 FIGURE 1. DP8392A Block Diagram 3.0 Functional Description Receiver then stays off only if within about 1 ms, the DC level from the low pass filter rises above the DC squelch threshold. Figure 2 illustrates the Receiver timing. The differential line driver provides ECL compatible signals to the DTE with typically 3 ns rise and fall times. In its idle state, its outputs go to differential zero to prevent DC standing current in the isolation transformer. The CTI consists of four main logical blocks: a) the Receiver - receives data from the coax and sends it to the DTE b) the Transmitter - accepts data from the DTE and transmits it onto the coax c) the Collision Detect circuitry - indicates to the DTE any collision on the coax d) the Jabber Timer - disables the Transmitter in case of longer than legal length packets 3.2 TRANSMITTER FUNCTIONS The Transmitter has a differential input and an open collector output current driver. The differential input common mode voltage is established by the CTI and should not be altered by external circuitry. The transformer coupling of TX g will satisfy this condition. The driver meets all IEEE 802.3/Ethernet Specifications for signal levels. Controlled rise and fall times (25 ns V g 5 ns) minimize the higher harmonic components. The rise and fall times are matched to minimize jitter. The drive current levels of the DP8392A meet the tighter recommended limits of IEEE 802.3 and are set by a built-in bandgap reference and an external 1% resistor. An on chip isolation diode is provided to reduce the Transmitter’s coax load capacitance. For Ethernet compatible applications, an external isolation diode (see Figure 4 ) may be added to further reduce coax load capacitance. In Cheapernet compatible applications the external diode is not required as the coax capacitive loading specifications are relaxed. The Transmitter squelch circuit rejects signals with pulse widths less than typically 20 ns (negative going), or with levels less than b175 mV. The Transmitter turns off at the end of the packet if the signal stays higher than b175 mV for more than approximately 300 ns. Figure 3 illustrates the Transmitter timing. 3.1 RECEIVER FUNCTIONS The Receiver includes an input buffer, a cable equalizer, a 4-pole Bessel low pass filter, a squelch circuit, and a differential line driver. The buffer provides high input impedance and low input capacitance to minimize loading and reflections on the coax. The equalizer is a high pass filter which compensates for the low pass effect of the cable. The composite result of the maximum length cable and the equalizer is a flatband response at the signal frequencies to minimize jitter. The 4-pole Bessel low pass filter extracts the average DC level on the coax, which is used by both the Receiver squelch and the collision detection circuits. The Receiver squelch circuit prevents noise on the coax from falsely triggering the Receiver in the absence of the signal. At the beginning of the packet, the Receiver turns on when the DC level from the low pass filter is lower than the DC squelch threshold. However, at the end of the packet, a quick Receiver turn off is needed to reject dribble bits. This is accomplished by an AC timing circuit that reacts to high level signals of greater than typically 200 ns in duration. The 2 3.0 Functional Description (Continued) 3.3 COLLISION FUNCTIONS The collision circuitry consists of two buffers, two 4-pole Bessel low pass filters (section 3.1), a comparator, a heartbeat generator, a 10 MHz oscillator, and a differential line driver. Two identical buffers and 4-pole Bessel low pass filters extract the DC level on the center conductor (data) and the shield (sense) of the coax. These levels are monitored by the comparator. If the data level is more negative than the sense level by at least the collision threshold (Vth), the collision output is enabled. At the end of every transmission, the heartbeat generator creates a pseudo collision for a short time to ensure that the collision circuitry is properly functioning. This burst on collision output occurs typically 1.1 ms after the transmission, and has a duration of about 1 ms. This function can be disabled externally with the HBE (Heartbeat Enable) pin to allow operation with repeaters. The 10 MHz oscillator generates the signal for the collision and heartbeat functions. It is also used as the timebase for all the jabber functions. It does not require any external components. The collision differential line driver transfers the 10 MHz signal to the CD g pair in the event of collision, jabber, or heartbeat conditions. This line driver also features zero differential idle state. 3.4 JABBER FUNCTIONS The Jabber Timer monitors the Transmitter and inhibits transmission if the Transmitter is active for longer than 20 ms (fault). It also enables the collision output for the fault duration. After the fault is removed, The Jabber Timer waits for about 500 ms (unjab time) before re-enabling the Transmitter. The transmit input must stay inactive during the unjab time. TL/F/7405 – 3 FIGURE 2. Receiver Timing TL/F/7405 – 4 FIGURE 3. Transmitter Timing 3 4.0 Connection Diagram Note 1: T1 is a 1:1 pulse transformer, L e 100 mH Pulse Engineering (San Diego) Part No. 64103 Valor Electronics (San Diego) Part No. 1101 or equivalent TL/F/7405 – 5 Top View Order Number DP8392AN See NS Package Number N16A FIGURE 4 4 5.0 Pin Descriptions Pin No. Name I/O Description 1 2 CD a * CDb O Collision Output. Balanced differential line driver outputs from the collision detect circuitry. The 10 MHz signal from the internal oscillator is transferred to these outputs in the event of collision, excessive transmission (jabber), or during CD Heartbeat condition. These outputs are open emitters; pulldown resistors to VEE are required. When operating into a 78X transmission line, these resistors should be 500X. In Cheapernet applications, where the 78X drop cable is not used, higher resistor values (up to 1.5k) may be used to save power. 3 6 RX a * RXb O Receive Output. Balanced differential line driver outputs from the Receiver. These outputs also require 500X pulldown resistors. 7 8 TX a * TXb I Transmit Input. Balanced differential line receiver inputs to the Transmitter. The common mode voltage for these inputs is determined internally and must not be externally established. Signals meeting Transmitter squelch requirements are waveshaped and output at TXO. 9 HBE I Heartbeat Enable. This input enables CD Heartbeat when grounded, disables it when connected to VEE. 11 12 RR a RRb I External Resistor. A fixed 1k 1% resistor connected between these pins establishes internal operating currents. 14 RXI I Receive Input. Connects directly to the coaxial cable. Signals meeting Receiver squelch requirements are equalized for inter-symbol distortion, amplified, and outputted at RX g . 15 TXO O Transmit Output. Connects either directly (Cheapernet) or via an isolation diode (Ethernet) to the coaxial cable. 16 CDS I Collision Detect Sense. Ground sense connection for the collision detect circuit. This pin should be connected separately to the shield to avoid ground drops from altering the receive mode collision threshold. 10 GND Positive Supply Pin. A 0.1 mF ceramic decoupling capacitor must be connected across GND and VEE as close to the device as possible. 4 5 13 VEE Negative Supply Pins. In order to make full use of the 3.5W power dissipation capability of this package, these pins should be connected to a large metal frame area on the PC board. Doing this will reduce the operating die temperature of the device thereby increasing the long term reliability. * IEEE names for CD g e CI g , RX g e DI g , TX g e DO g VEE pins are to be connected to a copper plane which should be included in the printed circuit board layout. Refer to National Semiconductor application note AN-442 (Ethernet/Cheapernet Physical Layer Made Easy) for complete board layout instructions. 5.1 P.C. BOARD LAYOUT The DP8392A package is uniquely designed to ensure that the device meets the 1 million hour Mean Time Between Failure (MTBF) requirement of the IEEE 802.3 standard. In order to fully utilize this heat dissipation design, the three 5 6.0 Absolute Maximum Ratings (Note 1) b 12V Supply Voltage (VEE) Package Power Rating at 25§ C 3.5 Watts* (PC Board Mounted) See Section 5 Derate linearly at the rate of 28.6 mW/§ C Input Voltage Storage Temperature Lead Temp. (Soldering, 10 seconds) Recommended Operating Conditions b 9v g 5% Supply Voltage (VEE) Ambient Temperature 0§ to 70§ C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. 0 to b12V b 65§ to 150§ C 260§ C *For actual power dissipation of the device please refer to section 7.0. 7.0 Electrical Characteristics VEE e b9V g 5%, TA e 0§ to 70§ C (Notes 2 & 3) Symbol Parameter Min IEE1 Supply current out of VEE pinÐnon transmitting IEE2 Supply current out of VEE pinÐtransmitting IRXI Receive input bias current (RXI) b2 ITDC Transmit output dc current level (TXO) 37 ITAC Transmit output ac current level (TXO) VCD Collision threshold (Receive mode) b 1.45 VOD Differential output voltage (RX g , CD g ) g 550 VOC Common mode output voltage (RX g , CD g ) b 1.5 VOB Diff. output voltage imbalance (RX g , CD g ) VTS Transmitter squelch threshold (TX g ) CX Input capacitance (RXI) RRXI Shunt resistanceÐnon transmitting (RXI) RTXO Shunt resistanceÐtransmitting (TXO) Typ Max Units b 85 b 130 mA b 125 b 180 mA a 25 mA 41 45 mA ITDC mA b 1.53 b 1.58 V g 1200 mV g 28 b 2.0 b 175 b 225 b 2.5 V g 40 mV b 300 mV 1.2 pF 100 KX 10 KX 8.0 Switching Characteristics VEE e b9V g 5%, TA e 0§ to 70§ C (Note 3) Symbol Parameter Fig Min Typ Max Units tRON Receiver startup delay (RXI to RX g ) 5 & 11 4 tRd Receiver propagation delay (RXI to RX g ) 5 & 11 15 tRr Differential outputs rise time (RX g , CD g ) 5 & 11 4 tRf Differential outputs fall time (RX g , CD g ) 5 & 11 4 ns tRJ Receiver & cable total jitter 10 g2 ns tTST Transmitter startup delay (TX g to TXO) 6 & 11 1 tTd Transmitter propagation delay (TX g to TXO) 6 & 11 25 tTr Transmitter rise time Ð10% to 90% (TXO) 6 & 11 25 tTf Transmitter fall time Ð90% to 10% (TXO) 6 & 11 25 ns tTM tTr and tTf mismatch 0.5 ns tTS Transmitter skew (TXO) g 0.5 ns tTON Transmit turn-on pulse width at VTS (TX g ) 6 & 11 20 ns tTOFF Transmit turn-off pulse width at VTS (TX g ) 6 & 11 250 ns tCON Collision turn-on delay 7 & 11 7 bits tCOFF Collision turn-off delay 7 & 11 fCD Collision frequency (CD g ) 7 & 11 tCP Collision pulse width (CD g ) 7 & 11 35 70 ns tHON CD Heartbeat delay (TX g to CD g ) 8 & 11 0.6 1.6 ms tHW CD Heartbeat duration (CD g ) 8 & 11 0.5 1.0 1.5 ms tJA Jabber activation delay (TX g to TXO and CD g ) 9 & 11 20 29 60 ms tJR Jabber reset unjab time (TX g to TXO and CD g ) 9 & 11 250 500 750 ms 8.0 bits 50 ns ns bits 50 ns ns 20 bits 12.5 MHz Note 1: Absolute maximum ratings are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the device should be operated at these limits. Note 2: All currents into device pins are positive, all currents out of device pins are negative. All voltages referenced to ground unless otherwise specified. Note 3: All typicals are given for VEE e b 9V and TA e 25§ C. 6 9.0 Timing and Load Diagrams TL/F/7405 – 6 FIGURE 5. Receiver Timing TL/F/7405 – 7 FIGURE 6. Transmitter Timing TL/F/7405 – 8 FIGURE 7. Collision Timing TL/F/7405 – 9 FIGURE 8. Heartbeat Timing 7 9.0 Timing and Load Diagrams (Continued) TL/F/7405 – 10 FIGURE 9. Jabber Timing Input jitter s g 1 ns RX g Output jitter s g 7 ns TL/F/7405 – 11 Difference s g 6 ns FIGURE 10. Receive Jitter Timing TL/F/7405 – 12 *The 50 mH inductance is for testing purposes. Pulse transformers with higher inductances are recommended (see Figure 4 ) FIGURE 11. Test Loads 8 9 DP8392A/NS32492A Coaxial Transceiver Interface 10.0 Physical Dimensions inches (millimeters) Lit. Ý103054 Molded Dual-In-Line Package (N) Order Number DP8392AN NS Package Number N16A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. 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