PI6C4911504-01 High Performance LVPECL Fanout Buffer Features Description ÎÎ4 LVPECL outputs The PI6C4911504-01 is a high performance fanout buffer device which supports up to 1.5GHz frequency. This device is ideal for systems that need to distribute low jitter clock signals to multiple destinations. ÎÎUp to 1.5GHz output frequency ÎÎUltra low additive phase jitter: < 0.04 ps (typ) ÎÎTwo selectable inputs ÎÎLow delay from input to output (Tpd typ. < 1.0ns) Applications ÎÎ2.5V / 3.3V power supply ÎÎNetworking systems including switches and Routers ÎÎIndustrial temperature support ÎÎHigh frequency backplane based computing and telecom ÎÎTSSOP-20 package platforms Block Diagram SYNC_OE Pullup Pin Configuration (20-Pin TSSOP) D LE REF_IN0+ REF_IN0- Pulldown REF_IN1+ REF_IN1- Pulldown IN_SEL Pullup Pullup Pulldown GND 1 20 Q0+ Q0+ Q0- SYNC_OE 2 19 Q0- IN_SEL 3 18 VDD Q1+ Q1- REF_IN0+ 4 17 Q1+ REF_IN0- 5 16 Q1- Q2+ Q2- REF_IN1+ 6 15 Q2+ REF_IN1- 7 14 Q2- nc 8 13 VDD nc 9 12 Q3+ 10 11 Q3- Q 0 1 Q3+ Q3- VDD 15-0027 1 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Pinout Table Pin # Pin Name 1 GND Power 2 SYNC_OE Input Pullup Synchronous clock enable. When High, clock outputs follow REF_IN. When low, Q+ outputs are forced low, Q- are forced high 3 IN_SEL Input Pulldown Clock input source selection pin REF_IN0+ 4, 5 REF_IN0REF_IN1+ 6, 7 REF_IN1- Type Input Input Description Ground Pulldown Differential clock input 0 Pullup Pulldown Differential clock input 1 Pullup 8, 9 NC - No connect 10, 13, 18 VDD Power Power supply Output LVPECL output clock 3 Output LVPECL output clock 2 Output LVPECL output clock 1 Output LVPECL output clock 0 Q3+ 11, 12 Q3Q2+ 14, 15 Q2Q1+ 16, 17 Q1Q0+ 19, 20 Q0- Function Table Table 1: Clock source input select function IN_SEL Function 0 REF_IN0 is the selected reference input 1 REF_IN1 is the selected reference input Table 2: SYNC_OE select function SYNC_OE Function 0 All outputs disabled. Q+ disabled low, Q- disabled High. 1 All outputs enabled. Pin Characteristics Symbol R PULLUP R PULLDOWN 15-0027 Parameter Min Typ Max Units Input Pullup Resistor 50 kΩ Input Pulldown Resistor 75 kΩ 2 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Maximum Ratings (Above which the useful life may be impaired. For user guidelines, not tested) Note: Storage temperature....................................................-55 to +150ºC Stresses greater than those listed under MAXIMUM RATINGS may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability. Supply Voltage to Ground Potential (VDD)............ -0.5 to +4.65V Inputs (Referenced to GND).............................. -0.5 to VDD+0.5V Clock Output (Referenced to GND)................. -0.5 to VDD+0.5V Soldering Temperature (Max of 10 seconds).....................+260ºC Latch up...................................................................................200mA ESD Protection (Input)................................... 2000 V min (HBM) Power Supply Characteristics and Operating Conditions Symbol Parameter Test Condition VDD Supply Voltage IDD Power Supply Current TA Ambient Operating Temperature Min. Typ. Max. Units 3.135 3.465 V 2.375 2.625 V 90 mA 85 °C Max. Units Outputs unloaded -40 LVCMOS/ LVTTL DC Characteristics Symbol VIH VIL Parameter Test Condition Min. Input High Voltage VDD = VIN = 3.465V 2 VDD+0.3 V VDD = VIN = 2.625V 1.6 VDD+0.3 V VDD = VIN = 3.465V -0.3 0.8 V VDD = VIN = 2.625V -0.3 0.6 V Input Low Voltage SYNC_OE IIH Input High Current IN_SEL SYNC_OE IIL Input Low Current IN_SEL 15-0027 Typ. VDD = VIN = 3.465V 5 VDD = VIN = 2.625V 5 VDD = VIN = 3.465V 150 VDD = VIN = 2.625V 150 VDD = VIN = 3.465V -150 VDD = VIN = 2.625V -150 VDD = VIN = 3.465V -5 VDD = VIN = 2.625V -5 3 www.pericom.com µA µA µA µA PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer DC Electrical Specifications - Differential Inputs Symbol Parameter Min. IIH Input High current IIL Input Low current VID Input Differential Amplitude (Vp-p) VCM Common mode input voltage Typ. Max. Units REF_IN- Input = VDD 5 µA REF_IN+ Input = VDD 150 µA REF_IN- Input = GND -150 µA REF_IN+ Input = GND -5 µA REF_IN0 REF_IN1 0.15 VDD -2.0 0.5 VDD -0.85 1.5 VDD V V DC Electrical Specifications- LVPECL Outputs Parameter Description VOH Output High voltage VOL Output Low voltage Conditions Min. Typ. Max. Units VDD = 3.3V ± 5% VDD -1.4 VDD -0.9 V VDD = 2.5V ± 5% VDD -1.6 VDD -0.8 V VDD = 3.3V ± 5% VDD -2.0 VDD -1.6 V VDD = 2.5V ± 5% VDD -2.0 VDD -1.5 V Max. Units 1500 MHz AC Electrical Specifications – Differential Outputs Parameter Description Conditions Min. Typ. FOUT Clock output frequency LVPECL Tr Output rise time From 20% to 80% 300 400 600 ps Tf Output fall time From 80% to 20% 300 400 600 ps TODC Output duty cycle Frequency<650MHz 48 VPP Output swing Single-ended Frequency<650MHz 400 Taddjitter Buffer additive jitter RMS Using 156.25MHz XO, 0.17ps jitter as source @3.3V TPhasejitter Total output jitter RMS Using 156.25MHz XO, 0.17ps jitter as source @3.3V TSK Output Skew 4 outputs devices, outputs in same tank, with same load, at DUT. TPD Propagation Delay TOD Valid to HiZ 100 ns TOE HiZ to valid 100 ns 52 0.05 % ps 0.23 ps 40 ps 1000 ps Notes: 1. This parameter is guaranteed by design 15-0027 4 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Phase Noise Plots fOUT = 156.25MHz Output phase noise (Dark Blue) vs Input Phase noise (light blue) Additive jitter is calculated at 156.25MHz~40fs RMS (12kHz to 20MHz). Additive jitter = √(Output jitter2 - Input jitter2) 15-0027 5 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Configuration Test Load Board Termination for LVPECL VDD ZO = 50Ω TLA L = 0 ~ 10in Device 100Ω TLA ZO = 50Ω 150Ω 15-0027 150Ω 6 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Application information Suggest for Unused Inputs and Outputs LVCMOS Input Control Pins Differential Clock Trace Routing It is suggested to add pull-up=4.7k and pull-down=1k for LVCMOS pins even though they have internal pull-up/down but with much higher value (>=50k) for higher reliability design. Always route differential signals symmetrically, make sure there is enough keep-out space to the adjacent trace (>20mil.). In 156.25MHz XO drives IC example, it is better routing differential trace on component side as the following. Differential +IN/-IN Input Pins They can be left floating if not used. Connect them 1k to GND is optional for the additional protection. GND 0.1uf Vcc Keep out board vias 2 150 3 4 GND Outputs 156.25M XO All unused outputs are suggested to be left open and not connected to any trace. This can lower the IC power supply power. 150 *100 5 6 *100 is optional if IC has GND REF_IN+ REF_INVDD Clock IC Device Power Decoupling & Routing IC routing for XO drive VDD Pin Decoupling Clock timing is the most important component in PCB design, so its trace routing must be planned and routed as a first priority in manual routing. Some good practices are to use minimum vias (total trace vias count <4), use independent layers with good reference plane and keep other signal traces away from clock traces (>20mil.) etc. As general design rule, each VDD pin must have a 0.1uF decoupling capacitor. For better decoupling, 1uF can be used. Locating the decoupling capacitor on the component side has better decoupling filter result as shown below. 14 GND 13 12 0.1uF 11 VDD 0.1uF GND VDD VDD GND 10 9 8 Decouple cap. on comp. side Clock IC Device Placement of Decoupling caps 15-0027 7 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer LVPECL and LVDS Input Interface CMOS Clock DC Drive Input LVPECL and LVDS DC/ AC Input LVCMOS clock has voltage Voh levels such as 3.3V, 2.5V, 1.8V. CMOS drive requires a Vcm design at the input: Vcm= ½ (CMOS V) as shown below 7. Rs =22 ~33ohm typically. LVPECL and LVDS clock input to this IC is connected as shown below. LVPECL/ LVDS Input CMOS DC Input Vcm Design 15-0027 8 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Device LVPECL Output Terminations LVPECL Output Popular Termination LVPECL Output AC Thevenin Termination The most popular LVPECL termination is 150ohm pull-down bias and 100ohm across at RX side. Please consult ASIC datasheet if it already has 100ohm or equivalent internal termination. If so, do not connect external 100ohm across as shown in below. This popular termination’s advantage is that it does not allow any bias through from Vcc. This prevents Vcc system noise coupling onto clock trace. LVPECL AC Thevenin terminations require a 150ohm pulldown before the AC coupling capacitor at the source as shown below. Note that pull-up/down resistor value is swapped compared to previous figure. This circuit is good for short trace (<5in.) application only. LVPECL Output AC Thenvenin Termination LVPECL Output Popular Termination LVPECL Output Drive HCSL Input LVPECL Output Thevenin Termination Using the LVPECL output to drive a HCSL input can be done using a typical LVPECL AC Thenvenin termination scheme. Use pull-up/down 450/60ohm to generate Vcm=0.4V for the HCSL input clock. This termination is equivalent to 50Ohm load as shown. Figure below shows LVPECL output Thevenin termination which is used for shorter trace drive (<5in.), but it takes Vcc bias current and Vcc noise can get onto clock trace. It also requires more component count. So it is seldom used today. LVPECL Thevenin Output Termination 15-0027 LVPECL Output Drive HCSL Termination 9 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer LVPECL Output V_swing Adjustment It is suggested to add another cross 100ohm at TX side to tune the LVPECL output V_swing without changing the optimal 150ohm pull-down bias. This form of double termination can reduce the V_swing in ½ of the original at the RX side. By fine tuning the 100ohm resistor at the TX side with larger values like 150 to 200ohm, one can increase the V_swing by > 1/2 ratio. Phase Jitter Phase noise is short-term random noise attached on the clock carrier and it is a function of the clock offset from the carrier, for example dBc/Hz@10kHz which is phase noise power in 1-Hz normalized bandwidth vs. the carrier power @10kHz offset. Integration of phase noise in plot over a given frequency band yields RMS phase jitter, for example, to specify phase jitter <=1ps at 12k to 20MHz offset band as SONET standard specification. PCIe Ref_CLK Jitter PCIe reference clock jitter specification requires testing via the PCI-SIG jitter tool, which is regulated by US PCI-SIG organization. The jitter tool has PCIe Serdes embedded filter to calculate the equivalent jitter that relates to data link eye closure. Direct peak-peak jitter or phase jitter test data, normally is higher than jitter measure using PCI-SIG jitter tool. It has high-frequency jitter and low-frequency jitter spec. limit. For more information, please refer to the PCI-SIG website: http://www.pcisig.com/ specifications/pciexpress/ LVPECL Output V_swing Adjustment Device Thermal Calculation LVPECL V_swing Adjustment using Rs Figure below shows the JEDEC thermal model in a 4-layer PCB. Another way to control V_swing is by adding serial Rs. Rs value is tunable between 22 to 33 ohm depending on application. This method may reduce the clock drive PCB trace in slower Tr/Tf . JEDEC IC Thermal Model Important factors to influence device operating temperature are: 1) The power dissipation from the chip (P_chip) is after subtracting power dissipation from external loads. Generally it can be the no-load device Idd LVPECL V_swing Adjustment using Rs Clock Jitter Definitions 2) Package type and PCB stack-up structure, for example, 1oz 4 layer board. PCB with more layers and are thicker has better heat dissipation Total jitter= RJ + DJ Random Jitter (RJ) is unpredictable and unbounded timing noise that can fit in a Gaussian math distribution in RMS. RJ test values are directly related with how long or how many test samples are available. Deterministic Jitter (DJ) is timing jitter that is predictable and periodic in fixed interference frequency. Total Jitter (TJ) is the combination of random jitter and deterministic jitter: , where is a factor based on total test sample count. JEDEC std. specifies digital clock TJ in 10k random samples. 15-0027 10 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Thermal calculation example To calculate Tj and Tc of PI6CV304 in an SOIC-8 package: Step 1: Go to Pericom web to find Ja=157 C/W, Jc=42 C/W http://www.pericom.com/support/packaging/packaging-mechanicals-and-thermal-characteristics/ 3) Chassis air flow and cooling mechanism. More air flow M/s and adding heat sink on device can reduce device final die junction temperature Tj The individual device thermal calculation formula: Tj =Ta + Pchip x Ja Tc = Tj - Pchip x Jc Step 2: Go to device datasheet to find Idd=40mA max. Ja ___ Package thermal resistance from die to the ambient air in C/W unit; This data is provided in JEDEC model simulation. An air flow of 1m/s will reduce Ja (still air) by 20~30% Jc ___ Package thermal resistance from die to the package case in C/W unit Tj ___ Die junction temperature in C (industry limit <125C max.) Step 3: P_total= 3.3Vx40mA=0.132W Step 4: If Ta=85C Tj= 85 + Ja xP_total= 85+25.9 = 105.7C Tc= Tj + Jc xP_total= 105.7- 5.54 = 100.1C Note: The above calculation is directly using Idd current without subtracting the load power, so it is a conservative estimation. For more precise thermal calculation, use P_unload or P_chip from device Iee or GND current to calculate Tj, especially for LVPECL buffer ICs that have a 150ohm pull-down and equivalent 100ohm differential RX load. Ta ___ Ambiant air température in C Tc ___ Package case temperature in C Pchip___ IC actually consumes power through Iee/GND current Thermal Information Symbol Description QJA Junction-to-ambient thermal resistance QJC Junction-to-case thermal resistance 15-0027 Condition Still air 84.0 OC/W 17.0 OC/W 11 www.pericom.com PI6C4911504-01 Rev A 2/27/15 PI6C4911504-01 High Performance LVPECL Fanout Buffer Packaging Mechanical: 20-Contact TSSOP (L) Ordering Information Ordering Number Package Code Package Description Operating Temperature PI6C4911504-01LIE L -40 to 85 °C Pb-free & Green 20-Contact TSSOP • Thermal characteristics can be found on the company web site at www.pericom.com/packaging/ • E = Pb-free and Green • X suffix = Tape/Reel 15-0027 12 www.pericom.com PI6C4911504-01 Rev A 2/27/15