TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS TECHNICAL NOTE DDR333 MEMORY DESIGN GUIDE FOR TWO-DIMM UNBUFFERED SYSTEMS DDR memory busses vary depending on the intended market for the finished product. Some products must support four or more registered DIMMs, some are pointto-point topologies. This document focuses on solutions requiring two unbuffered DIMMs operating at a data rate of 333 MHz and is intended to assist board designers with the development and implementation of their products. The document is split into two sections. The first section uses data gathered from a chipset and motherboard designed by Micron to provide a set of board design rules. These rules are meant to be a starting point for a board design. The second section details the process of determining the portion of the total timing budget allotted to the board interconnect. The intent is that board designers will use the first section to develop a set of general rules and then, through simulation, verify the design in their particular environment. of the address and command bus, so the system can have one or two DIMMs per copy. Further, the address bus can be clocked using 1T or 2T clocking. With 1T, a new command can be issued on every clock cycle. 2T timing will hold the address and command bus valid for two clock cycles. This reduces the efficiency of the bus to one command per two clocks, but it doubles the amount of setup and hold time. The data bus remains the same for all of the variations in the address bus. This design guide covers a DDR system using two unbuffered DIMMs, operating at a 333 MHz data rate and two variations of the address and command bus. The first variation covered is a system with two DIMMs on the address and command bus using 1T clocking. A block diagram of this topology is shown in Figure 1. The second variation is a system with two DIMMs on the address and command bus using 2T clocking. This topology is shown in Figure 2. Please note that the guidelines provided in this section are intended to provide a set of rules for board designers to follow. It is always advisable to simulate the final implementation to ensure proper functionality. Introduction Systems using unbuffered DIMMs can implement the address and command bus using various configurations. For example, some controllers have two copies Figure 1: Two-DIMM Unbuffered DDR333 MHz Topology 1T Address and Command Bus Figure 2: Two-DIMM Unbuffered DDR333 MHz Topology 2T Address and Command Bus VREF VREF TN-46-07 TN4607.fm - Rev. 12/02 CLK5, CLK5# Data 1 VTT Regulator DDR DIMM Parallel Termination Resistors CLK4, CLK4# Series Resistors VTT Regulator DDR DIMM CLK1, CLK1# CLK2, CLK2# CLK3, CLK3# Series Resistors Data CLK0, CLK0# DDR Memory Controller Series Resistors CLK5, CLK5# Parallel Termination Resistors CLK4, CLK4# DDR DIMM CLK1, CLK1# CLK2, CLK2# CLK3, CLK3# Series Resistors CLK0, CLK0# DDR Memory Controller DDR DIMM Command/Address Command/Address Series Resistors Capacitor to ground on each Address and Command signal. Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS DDR Signal Grouping The signals that compose a DDR memory bus can be broken into three unique groupings, each with their own configuration and routing rules. bus runs at a clock rate of 167 MHz. The address and command signals are captured at the DRAM using the memory clocks. For a system with two unbuffered DIMMs on a single address and command bus, the loading on these signals will differ greatly depending on the type and number of DIMMs installed. A twoDIMM channel loaded with two double-sided DIMMs has 36 loads on the address and command signals. Under this heavy loading, the slew rate on the address bus is slow. The reduced slew rate makes it difficult, if not impossible, to meet the setup and hold times at the DRAM. To address this issue, the controller can use 2T address timing—increasing the time available for the address command bus by one clock period. Note that CS and CKE timing are not changed between 1T and 2T addressing. Data Group: Data Strobe DQS[8:0], Data Mask DQM[8:0], Data DQ[63:0], and Check Bits CB[7:0] Address and Control Group: Bank Address BA[1:0], Address A[13:0], and Command Inputs RAS#, CAS#, and WE#. Note that Clock Enable CKE[3:0], and Chip Select S[3:0]# are also part of the command signals but they have different loading and timing. Clock Group: Differential Clocks CK[5:0] and CK#[5:0] Board Stackup A two-DIMM DDR channel can be routed on a four-layer board. The layout should be done using controlled impedance traces of Zo = 60 ohm (±10%) characteristic impedance. The example stackup is shown in Figure 3. The trace impedance is based on a 5-mil-wide trace and 1/2 oz. copper. Routing Rules It is important that the address and command lines be referenced to a solid ground or power plane. On a four-layer board, the address and command would typically be routed on the second signal layer referenced to a solid power plane. The system address and command signals should be ground or power referenced over the entire bus to provide a low-impedance current return path. The address and command signals should be kept from the data group signals, from the controller to the first DIMM. Address and command signals are captured at the DIMM using the clock signals, so they must maintain a length relationship to the clock signals at the DIMM. Figure 3: Sample Board Stackup Component Side - Signal Layer 1 (0.5 oz. cu.) 5.5 mil Pregreg Ground Plane (1 oz. cu.) Figure 4: DDR Address and Command Signal Group Routing Topology ~42 mil Core Pad on Die Pin on Package Address and Control 5.5 mil Pregreg Power Plane (1 oz. cu.) A Solder Side - Signal Layer 2 (0.5 oz. cu.) DDR Memory Controller B DIMM1 DIMM2 VTT Rs Rp C D E Address and Command Signals 2T Clocking On a DDR memory bus, the address and command signals are unidirectional signals driven by the memory controller. For DDR333, the address and command TN-46-07 TN4607.fm - Rev 12/02 2 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Table 1: Address and Command Signals 1T Clocking Address and Command Group Routing Rules On a DDR memory bus, the address and command signals are unidirectional signals always driven by the memory controller. For DDR333, the address runs at a clock rate of 167 MHz. The address and command signals are captured at the DRAM using the memory clocks. For a system with two unbuffered DIMMs on a single address and command bus, the loading on these signals will differ greatly depending on the type and number of DIMMs installed. A two-DIMM channel loaded with two double-sided DIMMs has 36 loads on the address and command signals. The heavy capacitive load causes a significant reduction in signal slew rate and voltage margin at the DRAM. The reduced voltage margin causes a reduction in timing margin. As a result, setup and hold times at the DRAM may not be met. To address the poor margin, Micron has developed a compensated bus topology. This topology uses a capacitor to ground in place of the series damping resistor. A block diagram of this topology is shown in Figure 7. Figure 5 and Figure 6 are scope captures taken off two address signals on the same system. The boxes drawn in the center of the address eye show the setup and hold times at VIH and VIL DC. Both signals are captured in a system populated with two double-sided DIMMs. This is the worst-case address loading situation in this type of system. All measurements are taken at room temperature and nominal voltage. The address signal in Figure 5 is using a series and parallel resistor topology. As one can see, the address signal has a slow slew rate and a low maximum VIH. The combined result is a severe reduction in address setup and hold times. Under corner conditions, it is possible for this architecture to violate the DRAM setup and hold times, resulting in unstable system operation. In Figure 6, the address line is using the compensated capacitor architecture. The scope capture clearly shows the improved signal quality and larger address valid window. LENGTH A = Obtain from DRAM controller vendor. (A is the length from the die pad to the ball on the ASIC package.) B = 1.5in.–2.8in. C = 0.4in.–0.6in. D = 0.425in. E = 0.2in.–0.55in. Total: A + B + C = 2.4in.–3.2in. LENGTH MATCHING ±100 mils of memory clock length at the DIMM* TRACE Trace Width = 5 mils Trace Space = 15 mils reducing to 11.5 mils going between the pins of the DIMM. Trace Space from DIMM pins = 7 mils Trace Space to other signal groups = 20 mils *This value is controller-dependent; see Routing Rules on page 8. Series Resistors (Rs) Location: The series resistors should be located near the first DIMM for ease of routing. Value: The value of Rs can vary depending on the bus topology. Range: 10 ohms–25 ohms* Recommended: 20 ohms* Parallel/Pull-up Resistor (Rp) Termination Resistor Location: The parallel termination resistors should be placed behind the last DIMM slot and attached to the VTT power island. Value: The value of the parallel resistor can vary depending on the bus topology. Range: 25 ohms–56 ohms* Recommended: 36 ohms* *A recommended value. A range of values is provided for simulation when there is a need to deviate from the recommendation. TN-46-07 TN4607.fm - Rev 12/02 3 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 5: Uncompensated Address Line Figure 7: DDR Address and Command Signal Group Routing Topology Pad on Die Pin on Package DIMM1 DIMM2 Address and Control A B C D E CCOMP DDR Memory Controller Table 2: VTT Rp Address and Command Group Routing Rules LENGTH A = Obtain from DRAM controller vendor. (A is the length from the die pad to the ball on the ASIC package.) B = 0.4in.–1.4in. C = 1.6in.–2.2in. D = 0.425in. E = 0.2in.–0.55in. Figure 6: Compensated Address Line Total: A + B + C = 2.4in.–3.2in. LENGTH MATCHING ±100 mils of memory clock length at the DIMM* TRACE Trace Space = 15 mils reducing to 11.5 mils going between the pins of the DIMM. Trace Space from DIMM pins = 7 mils Trace Space to other signal groups = 20 mils *This value is controller-dependent; see Routing Rules on page 8. Routing Rules mand signals are captured at the DIMM using the clock signals, so they must maintain a length relationship to the clock signals at the DIMM. It is important that the address and command lines be referenced to a solid ground or power plane. On a four-layer board, the address and command would typically be routed on the second signal layer referenced to a solid power plane. The system address and command signals should be ground or power referenced over the entire bus to provide a low-impedance current return path. The address and command signals should be kept from the data group signals, from the controller to the first DIMM. Address and com- Compensation Capacitor (CCOMP) Location: CCOMP should be located such that lengths B and C are close to equal. Value: The value of CCOMP can vary depending on the bus topology. Range: 45pF–82pF* Recommended: 82pF* TN-46-07 TN4607.fm - Rev 12/02 4 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Parallel/Pull-Up Resistor (Rp) Termination Resistor Table 3: Location: The parallel termination resistors should be placed behind the last DIMM slot and attached to the VTT power island. Value: The value of the parallel resistor can vary depending on the bus topology. Range: 25 ohms–56 ohms* Recommended: 36 ohms* *A recommended value. A range of values is provided for simulation when there is a need to deviate from the recommendation. Data to Data Strobe Grouping DATA DATA STROBE DATA MASK DQ[7:0] DQ[15:8] DQ[23:16] DQ[31:24] DQ[39:32] DQ[47:40] DQ[55:48] DQ[63:56] CB[7:0] DQS 0 DQS 1 DQS 2 DQS 3 DQS 4 DQS 5 DQS 6 DQS 7 DQS 8 DM 0 DM 1 DM 2 DM 3 DM 4 DM 5 DM 6 DM 7 DM 8 Figure 8: DDR Data Byte Lane Routing Topology Data Signals In a DDR system, the data is captured by the memory and the controller using the data strobe rather than the clock. To achieve the double data rate, data is captured on the rising and falling edges of the data strobe. Each eight bits of data has an associated data strobe (DQS) and a data mask bit (DM). Since the data is captured off the strobe, the data bits associated with the strobe must be length matched closely to their strobe bit. This group of data and data strobe is referred to as a byte lane. The length matching between byte lanes is not as tight as it is within the byte lane. Table 3 shows the data and data strobe byte lane groups. Figure 8 shows the signals in a single-byte lane and the bus topology for the data signals. Pad on Die Pin on Package DQ Byte Group X A DIMM1 DIMM2 VTT Rs B Rp C D E C D E C D E DQS[X] A B DM[X] A B DDR Memory Controller Table 4: Data Group Routing Rules Routing Rules LENGTH It is important that the data lines be referenced to a solid ground plane because they are operating at twice the frequency of the address and command signals. These high-speed data signals require a good ground return path to avoid degradation of signal quality due to inductance in the signal return path. The system memory signals should be ground referenced from the memory controller to the DIMM connectors and from DIMM connector to DIMM connector to provide a low-impedance current return path. This is accomplished by routing the data signals on the top layer for the entire length of the signal. The data signals should not have any vias. To help reduce cross talk noise, the data strobe signals are shielded on each side by a 5-mil ground trace. We recommend stitching shield track to ground every inch to reduce transient currents. A = Obtain from DRAM controller vendor. (A is the length from the die pad to the ball on the ASIC package.) B = 1.5in.–2.8in. C = 0.4in.–0.6in. D = 0.425in. E = 0.2in.–0.55in. Total: A + B + C = 2.4in.–3.2in. TN-46-07 TN4607.fm - Rev 12/02 LENGTH MATCHING IN DATA/STROBE BYTE LANE ±100 mils from data strobe LENGTH MATCHING BYTE LANE TO BYTE LANE ±0.5in. of memory clock length TRACE Trace Width = 5 mils Trace Space = 15 mils reducing to 11.5 mils going between the pins of the DIMM. Trace Space from DIMM pins = 7 mils Trace Space to other signal groups = 20 mils 5 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Clock Signals Figure 9: DDR Clock Signal Group Routing Topology The memory clocks CK[5:0] and CK#[5:0] are used by the DRAM on a DDR bus to capture the address and command data. Unbuffered DIMMs require three clock pairs per DIMM. Some DDR memory controllers will drive all of these clocks, and others will require an external clock driver to generate these signals. In this example, it is assumed that the memory controller will drive the six clock pairs required for a two-DIMM unbuffered system. Clocks are differential signals, so they do not get connected to VTT like the other signals of a DDR bus. The clocks are differential pairs and must be routed as a differential pair. Each clock pair is differentially terminated on the DIMM by a 120 ohm resistor. Figure 9 shows the routing topology used for the clocks. In this figure, only one of the three clock pairs required by each DIMM is shown. Pad on Die CK[2:0] A A DIMM1 DIMM2 Rs B CK#[2:0] B C C CK[5:3] A A B CK#[5:3] B C2 C2 DDR Memory Controller Routing Rules Series Resistors (Rs) The clocks are routed as a differential pair from the controller to the DIMM. The clocks are used to capture the address signals at the DIMM, so they must maintain a length relationship to the address signals at the DIMM they are connected to. Different controllers handle the address clock relationship differently— some controllers have the ability to adjust the address to clock delay and others use a fixed delay. Memory controllers with a variable delay can better center the clock in the address valid eye over varying load conditions. Controllers with a fixed delay may require different routing of the clocks to compensate for different loading on the clock versus the address. The rules in this section are based on a controller that has variable clock delay. Location: The series resistors should be located near the first DIMM for ease of routing. Value: The value of the series resistor can vary depending on the bus topology. Range: 10 ohms–25 ohms* Recommended: 20 ohms* Parallel/Pull-Up Resistor (Rp) Termination Resistor Location: The parallel termination resistors should be placed behind the last DIMM slot and attached to the VTT power island. Value: The value of the parallel resistor can vary depending on the bus lengths used. DDR Memory Power Supply Requirements Range: 25 ohms–56 ohms* A DDR bus implementation requires three separate power supplies. The DRAM and the memory portion of the controller require a 2.5-volt supply. The 2.5-volt supply provides power for the DRAM core and I/O as well as at least the I/O of the DRAM controller. The second power supply is VREF, which is used as a reference voltage by the DRAM and the controller. The third supply is VTT, which is the termination supply of the bus. Table 6 lists the tolerances of each of these supplies. Recommended: 36 ohms* *A recommended value. A range of values is provided for simulation when there is a need to deviate from the recommendation. TN-46-07 TN4607.fm - Rev 12/02 Pin on Package 6 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Table 5: MVTT Layout Recommendations Clock Group Routing Rules • Place the MVTT island on the component-side signals layer at the end of the bus behind the last DIMM slot. • Use a wide-island trace for current capacity. • Place VTT generator as close to termination resistors as possible to minimize impedance (inductance). • Place one or two 0.1µf decoupling caps by each termination RPACK on the MVTT island to minimize the noise on VTT. Other bulk (10µf–22µf ) decoupling is also recommended to be placed on the MVTT island. LENGTH A = Obtain from DRAM controller vendor. (A is the length from the die pad to the ball on the ASIC package.) B = 1.5in.–2.8in. C = 0.4in.–0.6in. C2 =0.825in.–1.025in. LENGTH MATCHING ±30 mils for CKE to CKE# ±30 mils clock pair to clock pair at the DIMM TRACE Trace Width = 10 mils Trace Space = 5 mils Trace Space to other signal groups = 20 mils MVREF Voltage The memory reference voltage, MVREF, requires approximately 3mA of current at a voltage level of 1/2 VDD with a tolerance shown in Table 6. VREF can be generated using a simple resistor divider with one percent or better accuracy. VREF must track 1/2 of VDD over voltage, noise, and temperature changes. • Peak-to-peak AC noise on VREF may not exceed ±2 percent VREF (DC). Series Resistor (Rs) Location: The series resistor is located near the driver. Value: The value of the series resistor can vary depending on the bus topology. Range: 22 ohms–25 ohms MVREF Layout Recommendations Recommended: 22 ohms • Use 30-mil trace between decoupling cap and destination. • Maintain a 25-mil clearance from other nets. • Simplify implementation by routing VREF on the top signal trace layer. • Isolate VREF and/or shield with ground. • Decouple using distributed 0.01µf and 0.1µf capacitors by the regulator, controller, and DIMM slots. Place one 0.01µf and 0.1µf near pin one of each DIMM. Place one 0.1µf near the source of VREF, one near the VREF pin on the controller, and two between the controller and the first DIMM. MVTT Voltage The memory termination voltage, MVTT, requires current at a voltage level of 1.25 VDC. See Figure 6 for the VTT tolerance. VTT must be generated by a regulator that is able to sink and source current while still maintaining the tight voltage regulation. • VREF and VTT must track variations in VDD over voltage, temperature, and noise ranges. • VTT of the transmitting device must track VREF of the receiving device. Table 6: SYMBOL VDD (V25) VREF VTT TN-46-07 TN4607.fm - Rev 12/02 Required Voltages PARAMETER Device Supply Voltage Memory Reference Voltage Memory Termination Voltage MIN TYPICAL MAX UNIT 2.3 (0.5 × VDD) - 25mV VREF - 640mV 2.5 0.5 × VDD VREF 2.7 (0.5 × VDD) + 25mV VREF + 40mV V V V 7 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Timing Budget DDR Data Write Budget The previous section is useful for getting an idea of how the DDR memory bus functions and the general relationship between the signals on the bus. However, if a design should deviate from the given example, the routing rules for the design can change. Since it is unlikely that every design will follow the given example exactly, it is important to simulate the design. One of the objectives of simulation is to determine if the design will meet the signal timing requirements of the DRAM and DDR controller. To meet this objective, a timing budget must be generated. This section shows how to use the data provided in the DDR DRAM and DDR controller data sheets to determine the amount of the total timing budget that the board interconnect can consume. Table 7 gives a breakdown of the timing budget for DDR WRITEs at 333 MHz. The portion of the budget consumed by the DRAM device and by the DDR controller is fixed and cannot be influenced by the board designer. The amount of the total budget remaining after subtracting the portion consumed by the DRAM and the controller is what remains for the board interconnect. This is the portion that is used to determine the bus routing rules. The different components of the board interconnect are outlined. The board designer can make trade-offs with trace spacing, length matching, resistor tolerance, etc., to determine the best interconnect solution. Table 7: DDR Write Budget ELEMENT SKEW COMPONENT Transmitter DRAM device (from spec) Interconnect Total Interconnect Total Budget Total Budget Consumed by Controller and DRAM Interconnect Budget SETUP HOLD UNITS Total Skew at Transmitter DH/tDS Total Device XTK (cross talk) - DQ 550 450 450 100 550 450 450 100 ps ps ps ps XTK (cross talk) - DQS 30 30 ps ISI - DQ ISI - DQS Path Matching 15 5 15 15 5 15 ps ps ps Input Capacitance Matching 95 95 ps RTERM VOH/VOL Skew (1%) Input Eye Reduction (VREF) 20 100 20 100 ps ps Strobe-to-Data Skew 10 +10 ps Interconnect Skew 3000/2 @ 333 MHz Transmitter + DRAM 390 1500 1000 390 1500 1000 ps ps ps Total - (transmitter + DRAM) 500 500 ps t COMMENTS From data sheet From data sheet 4 aggressors (a pair on each side of the victim) 1 shielded victim, 2 aggressors (PRBS) Within byte lane: 165 ps/in. × 0.1in.; motherboard routes account for memory controller package skew 4.0pF and 5.0pF loads, strobe and data shift differently ±75mV included in DRAM skew; additional = (±25mV)/(.5 V/ns); this includes DQ and DQS Strobe shifts relative to data (1010 pattern vs. PRBS) From simulation Must be greater than amount consumed by board interconnect NOTE: These are worst-case slow numbers (100C, 2.375V, slow process). TN-46-07 TN4607.fm - Rev 12/02 8 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Determining DRAM Write Budget Consumption Determining DDR Controller Write Budget Consumption The amount of the write budget consumed by the DRAM is easily obtained from the data sheets. The DRAM data sheet provides the data input hold time relative to strobe (tDH) and the data input setup time relative to strobe (tDS). These numbers are entered directly into the timing budgets for setup and hold. They account for all of the write timing budget consumed by the DRAM. To calculate the amount of the setup timing budget consumed by the DDR controller on a DRAM WRITE, find the value for tDQSU minimum. This is the minimum amount of time all data will be valid before the data strobe transitions shown in Figure 10. tDQSU should take clock asymmetry into account. In an ideal situation, tDQSU would be equal to 1/4 × tCK. The difference between 1/4 × tCK and tDQSU is the amount of the write timing budget consumed by the controller for setup. From this, the following equation is derived. Controller setup data valid reduction = 1/4 × tCK t DQSU. To calculate the hold time, use the same equation, but use tDQHD in place of tDQSU. Figure 10: Memory Write and ADDR/CMD Timing T0 T1 T2 T3 T4 T5 T6 tDQSS tADSU tADHD CK ADDR/ CK tDSH tDSS tWPST DQS DQ tDQSU TN-46-07 TN4607.fm - Rev 12/02 A A A A tDQHD 9 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS DDR Data Read Budget Table 8 gives a breakdown of the timing budget for DDR reads at 333 MHz. The portion of the budget consumed by the DRAM device and by the DDR controller is fixed and cannot be influenced by the board Table 8: designer. The amount of the total budget remaining after subtracting the portion consumed by the DRAM and the controller is what remains for the board interconnect. DDR Read Budget ELEMENT SKEW COMPONENT SETUP HOLD UNITS DRAM device (from spec) t 6 2.70 6 2.70 ns ns t 350 350 ps t 500 500 ps t 2.20 2.20 ns t 1.85 1.85 ns (tCK/2 - tDV)/2 Total DRAM Data Valid Reduction Total Skew at Receiver 575 575 ps 575 575 ps From data sheet 550 550 ps From data sheet XTK (cross talk) - DQ 70 70 ps XTK (cross talk) - DQS 35 35 ps ISI - DQ ISI - DQS Path Matching 50 15 20 50 15 20 ps ps ps 4 aggressors (a pair on each side of the victim) 1 shielded victim, 2 aggressors (PRBS) Spice-generated eye diagram Rterm VOH/VOL Skew (1%) Input Eye Reduction (VREF) 20 100 20 100 ps ps Total Skew at Interconnect 3000/2 @ 333 MHz Receiver + DRAM 310 1500 1125 310 1500 1125 ps ps ps Total - (transmitter + DRAM) 375 375 ps Clock t t HP ( CL/ CH[MIN] at 45/55) DQSQ QHS QH (tHP - tQHS) DV (tHP - tDQSQ - tQHS, or QH - tDQSQ) COMMENTS t DRAM Total Receiver (controller) Interconnect Total Interconnect Total Budget Total Budget Consumed by Controller and DRAM Interconnect Budget Within byte lane: 165 ps/in. × 0.1in.; MB routes acct. for MC pkg. skew ±75mV included in DRAM skew; additional = (±25 mV)/(.5 V/ns); this includes DQ and DQS From simulation Must be greater than amount consumed by board interconnect NOTE: These are worst-case slow numbers (100C, 2.375V, slow process). TN-46-07 TN4607.fm - Rev 12/02 10 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 11: DRAM Read Data Valid tCK/2 tHP = 3.0ns = 2.7ns (tCK@45/55) Clock Duty Cyle = 45/55% tQH tDQSQ = 350ps tQHS = 2.2ns = 500ps DVW = 1.85ns DQS DQ (last data valid) DQ (first data no longer valid) All DQs and DQS, collectively Data Valid Window Figure 12: Read Data Timing T1 T0 T2 T3 T4 CK tHP tHP tHP tDQSQ tHP tDQSQ tHP tDQSQ tHP tHP tDQSQ DQS D DQ (last data valid) D D D D D D DQ (byte), collectively tDV D tQH tDV tQH tDV Using the DRAM data sheet and filling in numbers for the timing parameters in Figure 11, the total data valid window at the DRAM can be calculated using the following equation: Figure 11 shows how the information from the DRAM data sheet affects the total data valid window as the data is driven from the DRAM device. This information is used in the timing budget to determine the amount of the total data timing budget that is consumed by the DRAM device. The total budget for the data is half the clock period. This time is halved again to determine the time allowed for setup and hold. TN-46-07 TN4607.fm - Rev 12/02 D tQH tDV D D D Determining DRAM Read Budget Consumption D D D tQH D D D D D D D D D D D D D DQ (first data no longer valid) D D D D DVW = tHP - tDQSQ - tQHS t CK/2 - DVW/2 = DRAM data valid reduction. The DRAM data valid reduction is used in the timing budget for setup and hold. 11 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Determining DDR Controller Read Budget Consumption Determining DRAM Address Budget Consumption When read data is received at the controller from the DRAM, the strobe is edge aligned with the data. It is the responsibility of the controller to delay the strobe and then use the delayed strobe to capture the read data. The controller will have some minimum value it can accept for a data valid window. Internally, the controller has a minimum setup and hold time that the data must maintain from the internally delayed strobe. Half the data valid window is the setup or hold time required by the controller plus any controllerintroduced signal skew and strobe centering uncertainty. The timing diagram example in Figure 12 shows the timing parameters required for calculating the data valid window. tDQSQ is the maximum delay from the last data signal to go valid after the strobe transitions. t QH is the minimum time all data must remain valid after strobe transitions. Use the following equation to obtain tDV: The portion of the address budget consumed by the DRAM is obtained by getting the value of tIS for setup and tIH for hold. tIH and tIS are the setup and hold times required by the DRAM inputs. For systems with heavy loading on the address and command lines, the value in the data sheet must be derated depending on the slew rate. For Micron DDR DRAM, the setup time is raised by 50ps for each 100 mV/ns that the slew rate drops below 0.5 V/ns. The hold time is not changed. t t Determining Controller Address Budget Consumption The DRAM controller will provide a minimum setup and hold time for the address and command signals with respect to clock. This is the amount of the setup and hold budget consumed by the controller. Clock to Data Strobe Relationship t DV = QH - DQSQ. The DDR DRAM and the DDR controller must move the data from the data strobe clocking domain into the DDR clock domain when the data is latched internally. Due to this requirement, the data strobe must maintain a relationship to the DDR clock. For the DDR DRAM, this relationship is specified by tDQSS. This timing parameter states that after a WRITE command, the data strobe must transition 0.75 to 1.25 × tCK. Figure 10 shows the DDR controller also specifies a t DQSS timing parameter. This is the time after the WRITE command that the data strobe will transition. For the controller in this example, tDQSS = ±0.06 × tCK. The following equation is used to calculate the amount of clock to data strobe skew that is left for consumption by the board interconnect: t Assuming DV is split evenly between setup and hold, the portion of the timing budget consumed by the controller for setup and hold is 1/2 tDV. For the controller used in this example, an even split between setup and hold can be assumed because the controller determining the center of the data eye during the bootup routine and the DLL maintains this relationship over temperature and voltage variations. Address Timing Budget Table 9 gives a breakdown of the timing budget for 1T address and command at a 167 MHz clock rate. The portion of the budget consumed by the DRAM device and the DDR controller is fixed and cannot be influenced by the board designer. The amount of the total budget remaining after subtracting the portion consumed by the DRAM and the controller is what remains for the board interconnect. TN-46-07 TN4607.fm - Rev 12/02 Interconnect budget = DRAM tDQSS - Controller DQSS t Using this equation, it is apparent that this is not one of the strict timing requirements of a DDR channel. If the clocks are routed so they are between the shortest and longest strobe lengths, the designer gains some leeway in the data strobe to data strobe byte lane routing restrictions. 12 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Table 9: Address Timing Budget ELEMENT SKEW COMPONENT Transmitter SETUP HOLD UNITS 550 550 ps Chipset Receiver Memory Controller Transmitter DRAM Skew 850 750 ps t Interconnect Cross Talk: Address 640 640 ps ISI: Address Cross Talk: Clock VREF: Reduction 690 25 50 690 25 50 ps ps ps Path Matching 15 15 ps Input Capacitance Matching 105 105 ps Compensating Capacitor Skew (5%) Rterm VOH/VOL Skew (1%) Total Skew at Interconnect 6000 @ 333 MHz Transmitter + DRAM 60 60 ps 10 1595 3000 1400 10 1595 3000 1300 ps ps ps ps Total - (Transmitter + DRAM) 1600 1700 ps Total Interconnect Total Budget Total Budget Consumed by Controller and DRAM Interconnect Budget COMMENTS IS, tIH from DRAM spec (slow edge). tIS: additional 50ps for every 0.1 V/ns below 0.5 V/ns (0.3 V/ns) 1 victim (1010...), 4 aggressors (PRBS) (PRBS) Spec. ±75mV included in DRAM skew; additional = (±25mV)/(.5 V/ns) Within byte lane: 165 ps/in. × 0.1in.; MB routes acct. for MC pkg. skew 1.5pF for 5 device, 2.5pF for 18 device (1610-1400) = 210 total Compensating capacitor 5% tolerance Estimator tool 333 MHz bit width NOTE: These are worst-case slow numbers (100C, 2.375V, slow process). Appendix: Simulation Result Data Data Bus Simulation Conditions STANDARD TERMINATION Rs = 20 Controller Ron = 15 DRAM Ron = 15 Rp = 36 ohms B = 2,200 mils C = 400 mils D = 425 mils E = 400 mils Rise Time = 750ps Data Rate = 333 MHz TN-46-07 TN4607.fm - Rev 12/02 13 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 13: SSTL READs Rs = 20 Rstub = 22 Rp = 36 Pitch = 0.425” Slot 1 ISI1 = 9 Apert21 = 2.496 DD SlewR1 = 1.42 DS ISI3 = 23 Apert23 = 2.493 SlewR3 = 1.43 ISI4 = 11 Apert24 = 2.404 SlewR4 = 1.19 ISI9 = 25 Apert29 = 2.551 SlewR9 = 1.64 ISI10 = 30 Apert210 = 2.556 SlewR10 = 1.69 SD ISI5 = 13 Apert25 = 2.471 SlewR5 = 1.33 ISI6 = 24 Apert26 = 2.464 SlewR61 = 1.37 Slot 2 ISI2 = 11 Apert22 = 2.434 DD SlewR2 = 1.27 DS SD Slot 1 ISI7 = 29 Apert27 = 2.477 SlewR7 = 1.37 SS D– ISI11 = 28 S– Apert211 = 2.559 SlewR11 = 1.67 ISI12 = 31 Apert212 = 2.556 SlewR12 = 1.75 Slot 2 ISI8 = 26 Apert28 = 2.446 TN-46-07 TN4607.fm - Rev. 12/02 SlewR8 = 1.31 SS –D 14 –S Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 14: SSTL Writes Rs = 20 Rstub = 22 Rp = 36 Pitch = 0.425” Slot 1 ISI1 = 37 Apert21 = 2.033 DD SlewR1 = 0.79 DS ISI3 = 21 Apert23 = 2.210 SlewR3 = 0.93 ISI4 = 20 Apert24 = 2.358 SlewR4 = 1.17 ISI9 = 3 Apert29 = 2.431 SlewR9 = 1.26 SD ISI5 = 23 Apert25 = 2.476 SlewR5 = 1.40 ISI6 = 26 Apert26 = 2.243 SlewR61 = 0.97 Slot 2 ISI2 = 38 Apert22 = 2.076 DD SlewR2 = 0.80 DS SD Slot 1 ISI7 = 4 Apert27 = 2.516 SlewR7 = 1.46 SS D– ISI11 = 3 S– Apert211 = 2.589 SlewR11 = 1.71 ISI12 = 3 Apert212 = 2.590 SlewR12 = 1.72 Slot 2 ISI8 = 5 Apert28 = 2.470 TN-46-07 TN4607.fm - Rev. 12/02 SlewR8 = 1.34 SS –D ISI10 = 8 Apert210 = 2.428 SlewR10 = 1.26 15 –S Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Address Bus Simulation Conditions STANDARD TERMINATION COMPENSATED Rs = 10 Controller Ron = 15 Rp = 33 ohms B = 2,750 mils C = 250 mils D = 425 mils E = 400 mils Rise Time = 700ps 2T Cycle @ 83 MHz A1 address line is simulated. Waveforms shown are @ U1 memory device for both the slots Fcap = 82pF Controller Ron = 15 (Except last slide, where it is 25) Rp = 33 ohms B = 1,500 mils C = 1,500 mils D = 425 mils E = 400 mils Rise Time = 700ps 1T Cycle @ 166 MHz A1 address line is simulated. Waveforms shown are @ U1 memory device for both the slots TN-46-07 TN4607p16.fm - Rev 12/02 16 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 15: Standard Termination, 2T Cycle Slot 1 5,0 5,5 5,9 5,18 TN-46-07 TN4607.fm - Rev. 12/02 ISI1 = 29 Apert21 = 11.036 SlewR1 = 0.72 ISI1 = 22 Apert21 = 10.670 SlewR1 = 0.52 ISI1 = 47 Apert21 = 10.403 SlewR1 = 0.43 ISI1 = 38 Apert21 = 10.115 SlewR1 = 0.36 9,0 9,5 9,9 9,18 ISI1 = 31 Apert21 = 10.634 SlewR1 = 0.49 ISI1 = 13 Apert21 = 10.389 SlewR1 = 0.42 ISI1 = 25 Apert21 = 10.165 SlewR1 = 0.38 ISI1 = 85 Apert21 = 9.831 SlewR1 = 0.32 17 18,0 18,5 18,9 18,18 ISI1 = 79 Apert21 = 10.279 SlewR1 = 0.41 ISI1 = 15 Apert21 = 9.961 SlewR1 = 0.34 ISI1 = 6 Apert21 = 9.743 SlewR1 = 0.31 ISI1 = 77 Apert21 = 9.392 SlewR1 = 0.27 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 16: Standard Termination, 2T Cycle Slot 2 0,5 5,5 5,9 5,18 ISI1 = 22 Apert21 = 10.982 SlewR1 = 0.68 ISI1 = 14 Apert25 = 10.578 SlewR5 = 0.48 ISI5 = 9 Apert251 = 10.255 SlewR51 = 0.39 ISI5 = 17 Apert25 = 9.866 SlewR5 = 0.32 TN-46-07 TN4607.fm - Rev. 12/02 0,9 9,5 9,9 9,18 ISI1 = 40 Apert21 = 10.608 SlewR1 = 0.49 ISI10 = 62 Apert210 = 10.249 SlewR10 = 0.39 ISI10 = 41 Apert210 = 10.025 SlewR10 = 0.35 ISI10 = 39 Apert210 = 9.596 SlewR10 = 0.29 18 0,18 18,5 18,9 18,18 ISI1 = 77 Apert21 = 10.244 SlewR1 = 0.40 ISI2 = 74 Apert22 = 9.974 Slew2 = 0.33 ISI2 = 6 Apert22 = 9.734 SlewR2 = 0.31 ISI2 = 22 Apert22 = 9.326 SlewR2 = 0.26 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 17: Compensated, 1T Cycle Slot 1 5,0 5,5 5,9 5,18 ISI1 = 311 Apert21 = 4.925 SlewR1 = 0.77 ISI1 = 124 Apert21 = 4.955 SlewR1 = 0.70 ISI1 = 226 Apert21 = 4.643 SlewR1 = 0.58 ISI1 = 418 Apert21 = 4.221 SlewR1 = 0.43 TN-46-07 TN4607.fm - Rev. 12/02 9,0 9,5 9,9 9,18 ISI1 = 145 Apert21 = 4.998 SlewR1 = 0.71 ISI1 = 19 Apert21 = 4.921 SlewR1 = 0.64 ISI1 = 126 Apert21 = 4.742 SlewR1 = 0.60 ISI1 = 283 Apert21 = 4.476 SlewR1 = 0.46 19 18,0 18,5 18,9 18,18 ISI1 = 117 Apert21 = 4.848 SlewR1 = 0.62 ISI1 = 160 Apert21 = 4.653 SlewR1 = 0.55 ISI1 = 133 Apert21 = 4.576 SlewR1 = 0.53 ISI1 = 65 Apert21 = 4.422 SlewR1 = 0.44 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 18: Compensated, 1T Cycle Slot 2 0,5 5,5 5,9 5,18 ISI1 = 326 Apert21 = 4.907 SlewR1 = 0.76 ISI5 = 45 Apert25 = 4.971 SlewR5 = 0.67 ISI5 = 127 Apert251 = 4.747 SlewR51 = 0.59 ISI5 = 291 Apert25 = 4.503 SlewR5 = 0.51 TN-46-07 TN4607.fm - Rev. 12/02 0,9 9,5 9,9 9,18 ISI1 = 148 Apert21 = 4.955 SlewR1 = 0.69 ISI10 = 199 Apert210 = 4.723 SlewR10 = 0.61 ISI10 = 186 Apert210 = 4.666 SlewR10 = 0.56 ISI10 = 369 Apert210 = 4.320 SlewR10 = 0.47 20 0,18 18,5 18,9 18,18 ISI1 = 133 Apert21 = 4.809 SlewR1 = 0.60 ISI2 = 333 Apert22 = 4.397 Slew2 = 0.51 ISI2 = 174 Apert22 = 4.531 SlewR2 = 0.54 ISI2 = 274 Apert22 = 4.217 SlewR2 = 0.45 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc. TN-46-07 DDR333 DESIGN GUIDE FOR TWO-DIMM SYSTEMS Figure 19: Compensated, 1T Cycle, Slot 1 (Ron = 25, to reduce excessive overshoot in lightly loaded cases) Slot 1 5,0 ISI1 = 414 Apert21 = 4.547 SlewR1 = 0.59 ISI1 = 453 Apert21 = 4.519 SlewR1 = 0.54 9,0 ISI1 = 328 Apert23 = 4.505 SlewR1 = 0.53 ISI1 = 361 Apert21 = 4.433 SlewR1 = 0.48 18,0 ISI1 = 264 Apert21 = 4.426 SlewR1 = 0.46 ISI1 = 204 Apert21 = 4.247 SlewR 1 = 0.42 Slot 2 0,5 0,9 0, 18 8000 S. Federal Way, P.O. Box 6, Boise, ID 83707-0006, Tel: 208-368-3900 E-mail: [email protected], Internet: http://www.micron.com, Customer Comment Line: 800-932-4992 Micron, the M logo, and the Micron logo are trademarks and/or service marks of Micron Technology, Inc. TN-46-07 TN4607.fm - Rev. 12/02 21 Micron Technology, Inc., reserves the right to change products or specifications without notice. ©2002, Micron Technology Inc.