PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination Features Description ÎÎFMAX < 2.5GHz The PI6C5922504 is a high-performance low-skew 1-to-4 LVDS fanout buffer. The CLK inputs accept LVPECL, LVDS, CML and SSTL signals. PI6C5922504 is ideal for clock distribution applications such as providing fanout for low noise Pericom oscillators. ÎÎ4 pairs of differential LVDS outputs ÎÎLow additive jitter, < 0.05ps (max) ÎÎInput CLK accepts: LVDS, LVDS, CML, SSTL input level ÎÎOutput to Output skew: <20ps ÎÎOperating Temperature: -40oC to 85oC ÎÎPower supply: 3.3V ±10% or 2.5V ±5% ÎÎPackaging (Pb-free & Green) TQFN available Pin Configuration Q0Q0+ VDD GND Block Diagram Q0+ Q0Q1+ Q1REF_IN+ VTH REF_IN- Q1+ Q1Q2+ Q2- Q2+ Q2EN D Q3+ Q3Q Q3+ Q3VDD LE 1 2 3 4 16 15 14 13 12 11 10 9 5 6 7 8 14-0127 1 REF_IN+ VTH VREF-AC REF_IN- EN ÎÎ16-pin PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination Pin Description(1) Pin # Name Type Description 1, 2 Q1+, Q1- Output Differential output pair, LVDS interface level. 3, 4 Q2+, Q2- Output Differential output pair, LVDS interface level. 5, 6 Q3+, Q3- Output Differential output pair, LVDS interface level. 7 VDD Power Core Power Supply 8 EN Input Synchronous Output Enable, with internal 25k-ohm pull-up resistor. Logic high selects enable, and logic low selects disable. 9 REF_IN- Input Differential IN negative input, AC and DC coupled 10 VREF-AC Output Reference Voltage: Biased to VDD-1.4V. Used when AC coupling inputs 11 VTH Output Differential pair IN center-tap node. Tie to VREF-AC for AC Coupled inputs. 12 REF_IN+ Input Differential IN positive input, AC and DC coupled 13 GND Power Ground 14 VDD Power Core Power Supply 15, 16 Q0+, Q0- Output Differential output pair, LVDS interface level. Functional Description REF_IN+ REF_IN- EN Q+ Q- 0 1 1 0 1 1 0 1 1 0 X X 0 0 1 14-0127 2 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination Maximum Ratings (Over operating free-air temperature range) Note: 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. Storage Temperature............................................... -65ºC to+155ºC Ambient Temperature with Power Applied..........-40ºC to+85ºC 3.3V Core Supply Voltage.......................................... -0.5 to +4.6V ESD Protection (HBM).......................................................... 2000V DC Characteristics Symbol Parameter Conditions Min VDD Power Supply Voltage TA Ambient Temperature IDD Power Supply Current R DIFF_IN Differential Input Resistance (IN+ to IN-) 90 VIH Input High Voltage VIL Typ Max Units 3.0 3.6 V 2.375 2.625 V -40 85 oC @3.3V± 10%, loaded 88 105 @2.5V± 5% loaded 58 75 100 110 Ω 1.2 VDD - 0.9 V Input Low Voltage 0.4 VIH-0.1 V VIN Input Voltage Swing 0.1 VDD V VDIFF_IN Differential Input Swing 0.2 VREF-AC Output Reference Voltage VDD -1.5 mA V VDD -1.3 VDD -1.15 V LVCMOS/LVTTL DC Characteristics (TA = -40oC to +85oC, VDD = 2.5V ±5% to 3.3V ±10%) Symbol Parameter VIH Input High Voltage 2.0 VDD VIL Input Low Voltage 0 0.8 IIH Input High Current -125 20 IIL Input Low Current -300 14-0127 Conditions 3 Min Typ Max Units V μA μA PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination LVDS DC Characteristics (TA = -40oC to +85oC, VDD = 3.3V ±10%, 2.5V ±5% ) Symbol Parameter VOUT Min Typ Max Units Output Voltage Swing 250 325 400 mV Differential Output Voltage Swing 500 650 800 mV VOCM Output Common Mode Voltage 1.15 1.35 V Delta VOCM Change in Common mode Voltage -100 100 mV VDIFF_ OUT Conditions AC Characteristics (TA = -40oC to +85oC, VDD = 3.3V ±10%, 2.5V ±5%) Symbol Parameter fmax Output Frequency tpd Propagation Delay Tsk Conditions Min Typ Max Units 2.5 Output-to-output Skew(2) GHz VIN < 400mV 370 470 570 VIN ≥ 400mV 300 410 500 Device to Device skew ps 20 ps 200 ps Ts Setup time 150 ps Th Hold time 150 ps tr/tf Output Rise/Fall time todc Output duty cycle VPP tj 20% - 80% 55 200 ps f ≤ 1 GHz 48 52 % 1 GHz ≤ f < 2.5 GHz 40 60 % Output Swing LVDS outputs 250 800 mV Buffer additive jitter RMS 156.25MHz with 12KHz to 20MHz integration range(3) 30 fs Notes: 1. Measured from the differential input to the differential output crossing point 2. Defined as skew between outputs at the same supply voltage and with equal loads. Measured at the output differential crossing point 3. Input source phase noise similar to phase noise plot in page 5 Thermal Information Symbol Description ΘJA Junction-to-ambient thermal resistance ΘJC Junction-to-case thermal resistance 14-0127 Condition Still air 57.7 °C/W 32.2 °C/W 4 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination Phase Noise Plots Configuration Test Load Board Termination for LVDS Outputs LVDS Buffer VCC Z o = 50 L = 0 ~ 10 in. 100 Z o = 50 14-0127 5 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination Output Swing vs Frequency Propagation Delay vs Temperature 14-0127 6 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination 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 design reliability. 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 Fig. 2. REF_IN=/ REF_IN- Input Pins They can be left floating if unused. For added reliability, connect 1kΩ to GND. GND Keep out board vias VDD 150 2 3 4 GND Outputs All unused outputs are suggested to be left open and not connected to any trace. This can lower the IC power supply power. 156.25M XO *100 is optional if IC has VDD Pin Decoupling 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 in Fig. 1. VDD VDD REF_INVDD Clock IC Device 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. 0.1uF 11 VDD 0.1uF REF_IN+ Clock timing is the most important component in PCB design, so its trace routing must be planned and routed as a first priority in 13 12 5 GND Fig 2: IC routing for XO drive 14 GND 150 *100 6 Power Decoupling & Routing GND 0.1uf GND 10 9 8 Decouple cap. on comp. side Clock IC Device Fig 1: Placement of Decoupling caps 14-0127 7 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination LVPECL and LVDS Input Interface LVPECL and LVDS DC Input HCSL AC-Coupled Input LVPECL and LVDS clock input to this IC is connected as shown in the Fig. 3. It is suggested to use AC coupling to buffer PCIe HCSL 100MHz clock since its V_cm is relatively low at about 0.4V, as shown in Fig. 6. REF_IN+ 50 *150 Zo =100 REF_IN- *150 33 33 VTH LVPECL Drive VREF-AC *150 removed for LVDS REF_IN+ 50 50 HCSL 50 0.01u Zo =100 REF_IN- 0.01u 50 + - VDD VTH 0.01uf PCIe Ref_CLK Device IC Device IC Fig 6: HCSL AC-Coupled Input Interface LVPECL and LVDS AC Input LVPECL and LVDS AC drive to this clock IC requires the use of the VREF-AC output to recover the DC bias for the IC input as shown in Fig. 4 0.01u CMOS Clock DC Drive 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 in Fig. 7. Rs =22 ~33ohm typically. REF_IN+ 50 0.01u + - VREF-AC Fig 3: LVPECL/ LVDS Input *150 50 Zo =100 REF_IN- *150 VDD LVPECL Drive VTH 0.01uf Rs 50 + CMOS Driver VREF-AC *150 removed for LVDS Zo REF_IN+ Ro VDD 3.3V 3.3V, 2.5V, 1.8V Device IC Fig 4: LVPECL/ LVDS AC Coupled Input REF_INVcm Rup 0.1u Rdn Diff. Input VTH Vcm design CML AC-Coupled Input CMOS V CML AC-coupled drive requires a connection to VREF-AC as shown in Fig. 5. The CML DC drive is not recommended as different vendors have different CML DC voltage level. CML is mostly used in AC coupled drive configuration for data and clock signals. Rup Rdn VREF-AC Vcm 3.3V 1k 1k 1.65V 2.5V 1k 610 1.25V 1.8V 1k 380 0.9V Fig 7: CMOS DC Input Vcm Design REF_IN+ 0.01u 50 CML 0.01u Zo =100 REF_IN- VDD CML AC-Coupled VTH 0.01uf 50 + - VREF-AC Device IC Fig 5: CML AC-Coupled Input Interface 14-0127 8 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination 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 Fig. 8. This popular termination’s advantage is that it does not allow any bias through from VDD. This prevents VDD system noise coupling onto clock trace. LVPECL AC Thevenin terminations require a 150ohm pulldown before the AC coupling capacitor at the source as shown in Fig. 10. Note that pull-up/down resistor value is swapped compared to Fig. 9. This circuit is good for short trace (<5in.) application only. Fig. 10 LVPECL Output AC Thenvenin Termination Fig. 8 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 in Fig. 11. Fig. 9 shows LVPECL output Thevenin termination which is used for shorter trace drive (<5in.), but it takes VDD bias current and VDD noise can get onto clock trace. It also requires more component count. So it is seldom used today. Fig. 9 LVPECL Thevenin Output Termination 14-0127 Fig. 11 LVPECL Output Drive HCSL Termination 9 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination 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 in Fig. 12. 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. Device Thermal Calculation Fig. 13 shows the JEDEC thermal model in a 4-layer PCB. Fig. 13 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 Fig. 12 LVPECL Output V_swing Adjustment 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 Clock Jitter Definitions 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 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. The individual device thermal calculation formula: Tj =Ta + Pchip x Ja Tc = Tj - Pchip x Jc 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 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. 14-0127 Tj ___ Die junction temperature in C (industry limit <125C max.) Ta ___ Ambiant air température in C Tc ___ Package case temperature in C Pchip___ IC actually consumes power through Iee/GND current 10 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination 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/ Step 2: Go to device datasheet to find Idd=40mA 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. 14-0127 11 PI6C5922504 Rev A 08/14/2014 PI6C5922504 2.5 GHz 1:4 LVDS Fanout Buffer with Internal Termination Packaging Mechanical: 16-pin TQFN (ZH) Ordering Information(1,2,3) Ordering Code Package Code Package Description PI6C5922504ZHIE ZH Pb-free & Green, 16-pin QFN Notes: 1. Thermal characteristics can be found on the company web site at www.pericom.com/packaging/ 2. E = Pb-free & Green 3. X suffix = Tape/Reel Pericom Semiconductor Corporation • 1-800-435-2336 • www.pericom.com 14-0127 12 PI6C5922504 Rev A 08/14/2014