FEMTOCLOCK® NG Crystal-to-LVDS/HCSL Clock Synthesizer ICS841N254I DATA SHEET General Description Features The ICS841N254I is a 4-output clock synthesizer designed for S-RIO 1.3 and 2.0 reference clock applications. The device generates four copies of a selectable 250MHz, 156.25MHz, 125MHz or 100MHz clock signal with excellent phase jitter performance. The four outputs are organized in two banks of two LVDS and two HCSL ouputs.The device uses IDT’s fourth generation FemtoClock® NG technology for an optimum of high clock frequency and low phase noise performance, combined with a low power consumption and high power supply noise rejection. The synthesized clock frequency and the phase-noise performance are optimized for driving RIO 1.3 and 2.0 SerDes reference clocks. The device supports 3.3V and 2.5V voltage supplies and is packaged in a small 32-lead VFQFN package. The extended temperature range supports wireless infrastructure, telecommunication and networking end equipment requirements. • • Fourth generation FemtoClock® (NG) technology • • Four differential clock outputs (two LVDS and two HCSL outputs) • RMS phase jitter @ 156.25MHz, using a 25MHz crystal (1MHz - 20MHz): 0.27ps (typical) • RMS phase jitter @ 156.25MHz, using a 25MHz crystal (12kHz - 20MHz): 0.32ps (typical) • • • • Power supply noise rejection PSNR: -50dB (typical) • -40°C to 85°C ambient operating temperature Selectable 250MHz, 156.25MHz, 125MHz or 100MHz output clock synthesized from a 25MHz fundamental mode crystal Crystal interface designed for 25MHz, parallel resonant crystal LVCMOS interface levels for the frequency select input Full 3.3V or 2.5V supply voltage Available in both standard (RoHS 5) and Lead-free (RoHS 6) packages 0 1 125MHz 1 0 100MHz 1 1 250MHz GND nQB1 156.25MHz QB1 0 (default) VDDOB 0 (default) nQB0 F_SEL0 Pin Assignment GND F_SEL1 Output Frequency with fXTAL = 25MHz VDD Inputs QB0 Function Table 32 31 30 29 28 27 26 25 VDD 1 nc 2 VDDA 3 nc 4 NOTE: F_SEL[1:0] are asynchronous controls. GND 5 REF_CLK 6 24 IREF 23 GND ICS841N254I 32-lead VFQFN K Package 5mm x 5mm x 0.925mm package body Top View nOEA 7 XTAL_IN 1 OSC 0 XTAL_OUT REF_CLK REF_SEL BYPASS F_SEL[0:1] nOEA nOEB IREF Pulldown PFD & LPF 1 Pulldown ÷N FemtoClock® NG VCO 625MHz 0 ÷25 21 QA0 20 VDDOA 19 nQA1 18 QA1 VDD 8 QA0 nQA0 LVDS QA1 nQA1 LVDS QB0 nQB0 HCSL QB1 nQB1 HCSL F_SEL1 F_SEL0 BYPASS VDD XTAL_OUT XTAL_IN 10 11 12 13 14 15 16 REF_SEL 17 GND 9 nOEB Block Diagram 22 nQA0 Pulldown Pulldown 2 Pulldown Pulldown ICS841N254AKI REVISION A APRIL 18, 2011 1 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Table 1. Pin Descriptions Number Name Type Description 1, 8, 13, 32 VDD Power 2, 4 nc Unused 3 VDDA Power Analog power supply. 5, 17, 23, 25, 31 GND Power Power supply ground. 6 REF_CLK Input Pulldown Alternative single-ended reference clock input. LVCMOS/LVTTL interface levels. 7 nOEA Input Pulldown Output enable input. See Table 3D for function. LVCMOS/LVTTL interface levels. 9 nOEB Input Pulldown Output enable input. See Table 3E for function. LVCMOS/LVTTL interface levels. 10 REF_SEL Input Pulldown Reference select input. See Table 3B for function. LVCMOS/LVTTL interface levels. 11, 12 XTAL_IN, XTAL_OUT Input 14 BYPASS Input Pulldown Bypass mode select pin. See Table 3C for function. LVCMOS/LVTTL interface levels. 15, 16 F_SEL0, F_SEL1 Input Pulldown Frequency select pin. See Table 3A for function. LVCMOS/LVTTL interface levels. 18, 19 QA1, nQA1 Output Differential clock output. LVDS interface levels. 20 VDDOA Power Output supply pin for QAx outputs. 21, 22 QA0, nQA0 Output Differential clock output. LVDS interface levels. 24 IREF Input 26, 27 nQB1, QB1 Output Differential clock output. HCSL interface levels. 28 VDDOB Power Output supply pin for QBx outputs. 29, 30 nQB0, QB0 Output Differential clock output. HCSL interface levels. Core supply pins. No connect. Crystal oscillator interface. XTAL_IN is the input, XTAL_OUT is the output. External fixed precision resistor (475Ω) from this pin to ground provides a reference current used for differential current-mode QBx, nQBx clock outputs. NOTE: Pulldown refers to internal input resistors. See Table 2, Pin Characteristics, for typical values. Table 2. Pin Characteristics Symbol Parameter CIN Input Capacitance 4 pF RPULLDOWN Input Pulldown Resistor 51 kΩ ICS841N254AKI REVISION A APRIL 18, 2011 Test Conditions 2 Minimum Typical Maximum Units ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Function Tables Table 3A. Output Divider and Output Frequency Inputs F_SEL1 F_SEL0 Operation fOUT with fREF = 25MHz 0 (default) 0 (default) fOUT = fREF * 25 ÷ 4 156.25MHz 0 1 fOUT = fREF * 5 125MHz 1 0 fOUT = fREF * 4 100MHz 1 1 fOUT = fREF * 10 250MHz NOTE: F_SEL[1:0] are asynchronous controls. Table 3B. PLL Reference Clock Select Function Table Input REF_SEL Operation 0 (default) The crystal interface is selected as reference clock 1 The REF_CLK input is selected as reference clock NOTE: REF_SEL is an asynchronous control. Table 3C. PLL BYPASS Function Table Input BYPASS Operation 0 (default) PLL is enabled. The reference frequency fREF is multiplied by the PLL feedback divider of 25 and then divided by the selected output divider N. 1 PLL is bypassed. The reference frequency fREF is divided by the selected output divider N. AC specifications do not apply in PLL bypass mode. NOTE: BYPASS is an asynchronous control. Table 3D. nOEA Output Enable Function Table Input nOEA Operation 0 (default) QA0, nQA0 and QA1, nQA1 outputs are enabled 1 QA0, nQA0 and QA1, nQA1 outputs are disabled (high-impedance) NOTE: nOEA is an asynchronous control. Table 3E. nOEB Output Enable Function Table Input nOEB Operation 0 (default) QB0, nQB0 and QB1, nQB1 outputs are enabled 1 QB0, nQB0 and QB1, nQB1 outputs are disabled (high-impedance) NOTE: nOEB is an asynchronous control. ICS841N254AKI REVISION A APRIL 18, 2011 3 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Absolute Maximum Ratings NOTE: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These ratings are stress specifications only. Functional operation of product at these conditions or any conditions beyond those listed in the DC Characteristics or AC Characteristics is not implied. Exposure to absolute maximum rating conditions for extended periods may affect product reliability. Item Rating Supply Voltage, VDD 3.6V Inputs, VI XTAL_IN Other Inputs 0V to 2V -0.5V to VDD + 0.5V Outputs, VO (HCSL) -0.5V to VDD + 0.5V Outputs, IO (LVDS) Continuous Current Surge Current 10mA 15mA Package Thermal Impedance, θJA 37.7°C/W (0 mps) Storage Temperature, TSTG -65°C to 150°C DC Electrical Characteristics Table 4A. Power Supply DC Characteristics, VDD = VDDOA = VDDOB = 3.3V±5% or 2.5V±5%, TA = -40°C to 85°C Symbol Parameter Test Conditions Minimum Typical Maximum Units VDD Core Supply Voltage 3.135 3.3 3.465 V 2.375 2.5 2.625 V VDDA Analog Supply Voltage VDD – 0.30 3.3 VDD V VDD – 0.30 2.5 VDD V VDDOA&B Output Supply Voltage 3.135 3.3 3.465 V 2.375 2.5 2.625 V IDDA Analog Supply Current 30 mA IDD Power Supply Current 113 mA IDDOA&B Output Supply Current 72 mA Table 4B. LVCMOS/LVTTL Input DC Characteristics, VDD = VDDOA = VDDOB = 3.3V±5% or 2.5V±5%, TA = -40°C to 85°C Symbol Parameter VIH Input High Voltage VIL Input Low Voltage IIH Input High Current nOEA, nOEB, BYPASS, REF_SEL, REF_CLK, F_SEL[1:0] VDD = VIN = 2.625V or 3.465V IIL Input Low Current nOEA, nOEB, BYPASS, REF_SEL, REF_CLK, F_SEL[1:0] VDD = 2.625V or 3.465V, VIN = 0V ICS841N254AKI REVISION A APRIL 18, 2011 Test Conditions Minimum VDD = 3.3V Maximum Units 2 VDD + 0.3 V VDD = 2.5V 1.7 VDD + 0.3 V VDD = 3.3V -0.3 0.8 V VDD = 2.5V -0.3 0.7 V 150 µA 4 -5 Typical µA ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Table 4C. LVDS 3.3V DC Characteristics, VDD = VDDOA = 3.3V ± 5% or 2.5V ± 5%, TA = -40°C to 85°C Symbol Parameter VOD Differential Output Voltage ∆VOD VOD Magnitude Change VOS Offset Voltage ∆VOS VOS Magnitude Change Test Conditions Minimum Typical 200 1.1 Maximum Units 550 mV 50 mV 1.3 V 50 mV Maximum Units Table 5. Crystal Characteristics Parameter Test Conditions Mode of Oscillation Minimum Typical Fundamental Frequency 25 MHz Equivalent Series Resistance (ESR) 80 Ω Shunt Capacitance 7 pF ICS841N254AKI REVISION A APRIL 18, 2011 5 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Table 6. AC Characteristics, VDD = VDDOA = VDDOB = 3.3V±5% or 2.5V±5%, TA = -40°C to 85°C Symbol Parameter fOUT Output Frequency fREF Reference Frequency tjit(Ø) ΦN Test Conditions RMS Phase Jitter (Random); NOTE 1 Single-Side Band Noise Power Minimum Units MHz F_SEL [1:0] = 01 125 MHz F_SEL [1:0] = 10 100 MHz F_SEL [1:0] = 11 250 MHz REF_CLK 25 MHz 156.25MHz, Integration Range: 1MHz – 20MHz 0.27 ps 156.25MHz, Integration Range: 12kHz – 20MHz 0.32 ps 125MHz, Integration Range: 1MHz – 20MHz 0.33 ps 125MHz,Integration Range: 12kHz – 20MHz 0.37 ps 156.25MHz, Offset: 100Hz -91.6 dBc/Hz 156.25MHz, Offset: 1kHz -120.8 dBc/Hz 156.25MHz, Offset: 10kHz -132.2 dBc/Hz 156.25MHz, Offset: 100kHz -135.0 dBc/Hz From DC to 50MHz -50 dB Between QAx/nQAx & QBx/nQBx 1.8 Power Supply Noise Rejection tsk(o) Output Skew NOTE 2, 3, 4 tsk(b) Bank Skew NOTE 2, 4, 5 tR / tF Output Rise/Fall Time tLOCK PLL Lock Time VRB Ring-back Voltage Margin; NOTE 6, 7 QBx, nQBx -100 tSTABLE Time before VRB is Allowed; NOTE 6, 7 QBx, nQBx 500 VMAX Absolute Maximum Output Voltage; NOTE 8, 9 QBx, nQBx VMIN Absolute Minimum Output Voltage; NOTE 8, 10 QBx, nQBx -300 VCROSS Absolute Crossing Voltage; NOTE 8, 11, 12 QBx, nQBx 100 ∆VCROSS Total Variation of VCROSS over all edges; NOTE 8, 11, 13 QBx, nQBx Rise/Fall Edge Rate; NOTE 6, 14 QBx, nQBx Output Duty Cycle; NOTE 15 Output Duty Cycle odc Maximum 156.25 PSNR QAx, nQAx Typical F_SEL [1:0] = 00 20% to 80% 100 2.7 ns 55 ps 400 ps 20 ms 100 mV ps 1150 mV mV 350 mV 140 mV 0.6 5.5 V/ns QBx, nQBx 47 53 % QAx, nQAx 47 53 % Measured between -150mV to 150mV NOTE: Electrical parameters are guaranteed over the specified ambient operating temperature range, which is established when the device is mounted in a test socket with maintained transverse airflow greater than 500 lfpm. The device will meet specifications after thermal equilibrium has been reached under these conditions. NOTES continued on next page. ICS841N254AKI REVISION A APRIL 18, 2011 6 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER NOTE: Characterized using a 25MHz crystal. NOTE 1: Please refer to the phase noise plots. NOTE 2: Defined as skew between outputs at the same supply voltage and with equal load conditions. Measured at the output differential cross points. NOTE 3: This parameter is defined in accordance with JEDEC Standard 65. NOTE 4: Defined as skew within a bank of outputs at the same voltage and with equal load conditions. NOTE 5: Measurement taken from differential waveform. NOTE 6: TSTABLE is the time the differential clock must maintain a minimum ±150mV differential voltage after rising/falling edges before it is allowed to drop back into the VRB ±100mV differential range. NOTE 7: Measurement taken from single ended waveform. NOTE 8: Defined as the maximum instantaneous voltage including overshoot. See Parameter Measurement Information Section. NOTE 9: Defined as the minimum instantaneous voltage including undershoot. See Parameter Measurement Information Section. NOTE 10: Measured at crossing point where the instantaneous voltage value of the rising edge of Q equals the falling edge of nQ. See Parameter Measurement Information Section. NOTE 11: Refers to the total variation from the lowest crossing point to the highest, regardless of which edge is crossing. Refers to all crossing points for this measurement. See Parameter Measurement Information Section. NOTE 12: Defined as the total variation of all crossing voltage of rising Q and falling nQ. This is the maximum allowed variance in the VCROSS for any particular system. See Parameter Measurement Information Section. NOTE 13: Measured from -150mV to +150mV on the differential waveform (derived from Q minus nQ). The signal must be monotonic through the measurement region for rise and fall time. The 300mV measurement window is centered on the differential zero crossing. ICS841N254AKI REVISION A APRIL 18, 2011 7 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER ➝ Typical Phase Noise at 156.25MHz (3.3V) Filter ➝ Noise Power dBc Hz 156.25MHz RMS Phase Jitter (Random) 12kHz to 20MHz = 0.32ps (typical) ➝ Raw Phase Noise Data Phase Noise Result by adding a filter to raw data Offset Frequency (Hz) ➝ Typical Phase Noise at 156.25MHz (3.3V) Filter Raw Phase Noise Data ➝ ➝ Noise Power dBc Hz 156.25MHz RMS Phase Jitter (Random) 1MHz to 20MHz = 0.27ps (typical) Phase Noise Result by adding a filter to raw data Offset Frequency (Hz) ICS841N254AKI REVISION A APRIL 18, 2011 8 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Parameter Measurement Information SCOPE 3.3V±5% POWER SUPPLY + Float GND – VDD, VDDOA, SCOPE Qx 2.5V±5% POWER SUPPLY + Float GND – VDDA VDD, VDDOA, Qx VDDA nQx nQx 3.3V LVDS Output Load AC Test Circuit 2.5V LVDS Output Load AC Test Circuit 3.3V±5% 3.3V±5% 3.3V±5% 3.3V±5% SCOPE VDD, VDDOB 50Ω 33Ω VDDA 49.9Ω IREF Qx VDDA HCSL 50Ω 50Ω IREF nQx GND 475Ω GND 49.9Ω 475Ω 2pF 0V 0V 0V 0V 50Ω 2pF HCSL 33Ω VDD, VDDOB This load condition is used for IDD, tjit(Ø), tsk(b) and tsk(o) measurements. 3.3V HCSL Output Load AC Test Circuit 3.3V HCSL Output Load AC Test Circuit 2.5V±5% 2.5V±5% 2.5V±5% 2.5V±5% SCOPE VDD, VDD, VDDOB 50Ω 33Ω VDDA IREF VDDOB VDDA Qx HCSL 49.9Ω 2pF HCSL 50Ω 33Ω 50Ω IREF nQx GND 475Ω GND 475Ω 49.9Ω 2pF 0V 0V 50Ω 0V This load condition is used for IDD, tjit(Ø), tsk(b) and tsk(o) measurements. 2.5V HCSL Output Load AC Test Circuit ICS841N254AKI REVISION A APRIL 18, 2011 0V 2.5V HCSL Output Load AC Test Circuit 9 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Parameter Measurement Information, continued Phase Noise Plot Noise Power nQA[0:1] QA[0:1] t PW Phase Noise Mask f1 Offset Frequency t odc = PERIOD t PW x 100% t PERIOD f2 RMS Jitter = Area Under the Masked Phase Noise Plot RMS Phase Jitter LVDS Output Duty Cycle/Pulse Width/Period nQX0 nQx QX1 Qx nQX0 nQy QX1 t sk(b) Qy t sk(o) Where X = Bank A or Bank B Output Skew Bank Skew TSTABLE Clock Period (Differential) VRB Positive Duty Cycle (Differential) +150mV VRB = +100mV 0.0V VRB = -100mV -150mV Negative Duty Cycle (Differential) 0.0V Q - nQ VRB Q - nQ TSTABLE Differential Measurement Points for Duty Cycle/Period Differential Measurement Points for Ringback ICS841N254AKI REVISION A APRIL 18, 2011 10 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Parameter Measurement Information, continued Rise Edge Rate Fall Edge Rate Rise Edge Rate Fall Edge Rate +150mV +150mV 0.0V 0.0V -150mV -150mV Q - nQ Q - nQ Differential Measurement Points for Rise/Fall Edge Rate HCSL Differential Measurement Points for Rise/Fall Time VMAX nQ nQ VCROSS_MAX VCROSS_DELTA VCROSS_MIN Q Q VMIN Single-ended Measurement Points for Absolute Cross Point/Swing Single-ended Measurement Points for Delta Cross Point VDD VDD out LVDS ➤ out ➤ out DC Input ➤ LVDS 100 ➤ VOD/∆ VOD VOS/∆ VOS out ➤ DC Input ➤ Differential Output Voltage Setup Offset Voltage Setup ICS841N254AKI REVISION A APRIL 18, 2011 11 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Applications Information Recommendations for Unused Input Pins Inputs: Outputs: REF_CLK Input LVDS Outputs For applications not requiring the use of the reference clock, it can be left floating. Though not required, but for additional protection, a 1kΩ resistor can be tied from the REF_CLK to ground. All unused LVDS output pairs can be either left floating or terminated with 100Ω across. If they are left floating, we recommend that there is no trace attached. Crystal Inputs Differential Outputs For applications not requiring the use of the crystal oscillator input, both XTAL_IN and XTAL_OUT can be left floating. Though not required, but for additional protection, a 1kΩ resistor can be tied from XTAL_IN to ground. All unused differential outputs can be left floating. We recommend that there is no trace attached. Both sides of the differential output pair should either be left floating or terminated. LVCMOS Control Pins All control pins have internal pulldowns; additional resistance is not required but can be added for additional protection. A 1kΩ resistor can be used. Interface to IDT S-RIO Switches The ICS841N254I is designed for driving the differential reference clock input (REF_CLK) of IDT’s S-RIO 1.3 and 2.0 switch devices. Both the LVDS and the HCSL outputs of the ICS841N254I have the low-jitter, differential voltage and impedance characteristics required to provide a high-quality 156.25MHz clock signal for both S-RIO 1.3 and 2.0 switch devices. Please refer to Figure 1A and Figure 1B for suggested interfaces. The interfaces differ by the driving output, LVDS and HCSL, and the corresponding source termination method. In both Figure 1A and 1B, the AC-coupling capacitors are mandatory by the IDT S-RIO switch devices. The differential REF_CLK input is internally re-biased and AC-terminated. Both interface circuits are optimized for 50Ω transmission lines and generate the voltage swing required to reliably drive the clock reference input of a IDT S-RIO switch. Please refer to IDT’s S-RIO device datasheet for more details. REF_CLK_P QAn LVDS nQAn T= 50Ω Figure 1A shows the recommended interface circuit for driving the 156.25MHz reference clock of an IDT S-RIO 2.0 switch by a LVDS output (QA0, QA1) of the ICS841N254I. The LVDS-to-differential interface as shown in Figure 1A does not require any external termination resistors: the ICS841N254I driver contains an internal source termination at QA0 and QA1. The differential REF_CLK input contains an internal AC-termination (RL) and re-bias (VBIAS). Figure 4B shows the interface circuit for driving the 156.25MHz reference clock of an IDT S-RIO 2.0 switch by an HCSL output of the ICS841N254I (QB0, QB1): The HCSL-to-differential interface requires external termination resistors (22...33Ω and 50Ω) for source termination, which should be placed close the driver (QB0, QB1). LI CI QBn HCSL nQBn RL VBIAS LI + REF_CLK - ICS841N254I CI ICS841N254I RL VBIAS 49.9 REF_CLK_N IDT S-RIO 1.3, 2.0 Switch LI + REF_CLK RL CI IDT S-RIO 1.3, 2.0 Switch Figure 1B. HCSL-to-S-RIO 2.0 Reference Clock Interface Figure 1A. LVDS-to-S-RIO 2.0 Reference Clock Interface ICS841N254AKI REVISION A APRIL 18, 2011 CI 22...33 RL LI T= 50Ω 22...33 49.9 REF_CLK_N REF_CLK_P 12 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Overdriving the XTAL Interface The XTAL_IN input can be overdriven by an LVCMOS driver or by one side of a differential driver through an AC coupling capacitor. The XTAL_OUT pin can be left floating. The amplitude of the input signal should be between 500mV and 1.8V and the slew rate should not be less than 0.2V/nS. For 3.3V LVCMOS inputs, the amplitude must be reduced from full swing to at least half the swing in order to prevent signal interference with the power rail and to reduce internal noise. Figure 2A shows an example of the interface diagram for a high speed 3.3V LVCMOS driver. This configuration requires that the sum of the output impedance of the driver (Ro) and the series resistance (Rs) equals the transmission line impedance. In addition, matched termination at the crystal input will attenuate the signal in half. This VCC can be done in one of two ways. First, R1 and R2 in parallel should equal the transmission line impedance. For most 50Ω applications, R1 and R2 can be 100Ω. This can also be accomplished by removing R1 and changing R2 to 50Ω. The values of the resistors can be increased to reduce the loading for a slower and weaker LVCMOS driver. Figure 2B shows an example of the interface diagram for an LVPECL driver. This is a standard LVPECL termination with one side of the driver feeding the XTAL_IN input. It is recommended that all components in the schematics be placed in the layout. Though some components might not be used, they can be utilized for debugging purposes. The datasheet specifications are characterized and guaranteed by using a quartz crystal as the input. XTAL_OUT R1 100 Ro Rs C1 Zo = 50 ohms XTAL_IN R2 100 Zo = Ro + Rs .1uf LVCMOS Driver Figure 2A. General Diagram for LVCMOS Driver to XTAL Input Interface XTAL_OUT C2 Zo = 50 ohms XTAL_IN .1uf Zo = 50 ohms LVPECL Driver R1 50 R2 50 R3 50 Figure 2B. General Diagram for LVPECL Driver to XTAL Input Interface ICS841N254AKI REVISION A APRIL 18, 2011 13 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER HCSL Recommended Termination Figure 3A is the recommended source termination for applications where the driver and receiver will be on a separate PCBs. This termination is the standard for PCI Express™ and HCSL output 0.5" Max Rs types. All traces should be 50Ω impedance single-ended or 100Ω differential. 1-14" 0-0.2" 22 to 33 +/-5% L1 L2 L4 L1 L2 L4 0.5 - 3.5" L5 L5 PCI Expres s PCI Express Connector Driver 0-0.2" L3 L3 PCI Express Add-in Card 49.9 +/- 5% Rt Figure 3A. Recommended Source Termination (where the driver and receiver will be on separate PCBs) Figure 3B is the recommended termination for applications where a point-to-point connection can be used. A point-to-point connection contains both the driver and the receiver on the same PCB. With a matched termination at the receiver, transmission-line reflections will 0.5" Max Rs 0 to 33 L1 be minimized. In addition, a series resistor (Rs) at the driver offers flexibility and can help dampen unwanted reflections. The optional resistor can range from 0Ω to 33Ω. All traces should be 50Ω impedance single-ended or 100Ω differential. 0-18" 0-0.2" L2 L3 L2 L3 0 to 33 L1 PCI Expres s Driver 49.9 +/- 5% Rt Figure 3B. Recommended Termination (where a point-to-point connection can be used) ICS841N254AKI REVISION A APRIL 18, 2011 14 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER LVDS Driver Termination A general LVDS interface is shown in Figure 4. Standard termination for LVDS type output structure requires both a 100Ω parallel resistor at the receiver and a 100Ω differential transmission line environment. In order to avoid any transmission line reflection issues, the 100Ω resistor must be placed as close to the receiver as possible. IDT offers a full line of LVDS compliant devices with two types of output structures: current source and voltage source. The standard termination schematic as shown in Figure 4 can be used with either type of output structure. If using a non-standard termination, it is recommended to contact IDT and confirm if the output is a current source or a voltage source type structure. In addition, since these outputs are LVDS compatible, the amplitude and common mode input range of the input receivers should be verified for compatibility with the output. + LVDS Driver LVDS Receiver 100Ω – 100Ω Differential Transmission Line Figure 4. Typical LVDS Driver Termination ICS841N254AKI REVISION A APRIL 18, 2011 15 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER VFQFN EPAD Thermal Release Path In order to maximize both the removal of heat from the package and the electrical performance, a land pattern must be incorporated on the Printed Circuit Board (PCB) within the footprint of the package corresponding to the exposed metal pad or exposed heat slug on the package, as shown in Figure 5. The solderable area on the PCB, as defined by the solder mask, should be at least the same size/shape as the exposed pad/slug area on the package to maximize the thermal/electrical performance. Sufficient clearance should be designed on the PCB between the outer edges of the land pattern and the inner edges of pad pattern for the leads to avoid any shorts. and dependent upon the package power dissipation as well as electrical conductivity requirements. Thus, thermal and electrical analysis and/or testing are recommended to determine the minimum number needed. Maximum thermal and electrical performance is achieved when an array of vias is incorporated in the land pattern. It is recommended to use as many vias connected to ground as possible. It is also recommended that the via diameter should be 12 to 13mils (0.30 to 0.33mm) with 1oz copper via barrel plating. This is desirable to avoid any solder wicking inside the via during the soldering process which may result in voids in solder between the exposed pad/slug and the thermal land. Precautions should be taken to eliminate any solder voids between the exposed heat slug and the land pattern. Note: These recommendations are to be used as a guideline only. For further information, please refer to the Application Note on the Surface Mount Assembly of Amkor’s Thermally/ Electrically Enhance Leadframe Base Package, Amkor Technology. While the land pattern on the PCB provides a means of heat transfer and electrical grounding from the package to the board through a solder joint, thermal vias are necessary to effectively conduct from the surface of the PCB to the ground plane(s). The land pattern must be connected to ground through these vias. The vias act as “heat pipes”. The number of vias (i.e. “heat pipes”) are application specific PIN PIN PAD SOLDER EXPOSED HEAT SLUG GROUND PLANE THERMAL VIA SOLDER LAND PATTERN (GROUND PAD) PIN PIN PAD Figure 5. P.C. Assembly for Exposed Pad Thermal Release Path – Side View (drawing not to scale) ICS841N254AKI REVISION A APRIL 18, 2011 16 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Schematic Layout Figure 6 shows an example of ICS41N254I application schematic. In this example, the device is operated at VDD= VDDOA = VDDOB = 3.3V. A 12pF parallel resonant 25MHz crystal is used. The load capacitance C1 = 5pF and C2 = 5pF are recommended for frequency accuracy. Depending on the parasitics of the printed circuit board layout, these values might require a slight adjustment to optimize the frequency accuracy. Crystals with other load capacitance specifications can be used. This will requiring adjusting C1 and C2. For this device, the crystal load capacitors are required for proper opteration. As with any high speed analog circuitry, the power supply pins are vulnerable to noise. To achieve optimum jitter performance, power supply isolation is required. The ICS841N254I provides separate power supplies to isolate from coupling into the internal PLL. In order to achieve the best possible filtering, it is recommended that the placement of the filter components be on the device side of the PCB as close to the power pins as possible. If space is limited, the 0.1uF capacitor in each power pin filter should be placed on the device side of the PCB and the other components can be placed on the opposite side. Logic Control Input Examples Set Logic Input to '1' VDD RU1 1K R4 Set Logic Input to '0' VDD 33 QB0 Zo = 50 + TL2 R5 VDD RU2 Not Install 33 nQB0 Zo = 50 - TL3 To Logic Input pins To Logic Input pins RD2 1K QB1 nQ B1 RD1 Not Install R6 50 VDDO C6 0.1u R7 50 Using for PCI Express Add-In Card R2 475 VDD VDD=3.3V R3 VDDA 10 VDDOA= VDDOB=3.3V U1 VD D GN D QB0 nQB0 VDD OB QB1 nQB1 GN D C7 10u HCSL Termination 32 31 30 29 28 27 26 25 VDD C3 0.01u C4 0.1u Optional VDD R9 33 R10 33 QB1 1 2 3 4 5 6 7 8 Q1 Ro ~ 7 Ohm R8 Zo = 50 Ohm REF_CLK nOEA 43 QB1_33 Zo = 50 nQA0 QA0 VDDO Driv er_LVCMOS nQB1_33 Zo = 50 - TL6 R11 50 LVDS Termination BYPASS F _S EL0 F _S EL1 nO EB R EF _SE L C1 5pF X1 25MHz XTAL_IN XTAL_OUT nQA1 3.3V 2 C9 0.1uF - BLM18BB221SN1 VDDO 1 Ferrite Bead C10 R1 100 C8 0.1u BLM18BB221SN1 1 + VDD C2 5pF 3.3V QA1 Zo = 100 Ohm Dif f erential 12pF R12 50 Using for PCI Express Point-to-Point Connection 9 10 11 12 13 14 15 16 C5 0.1u + TL5 nQB1 nO EB R E F _SEL X T A L_IN XT AL_O U T VD D BYPASS F _S EL0 F _S EL1 VDD IREF GND nQA0 QA0 VDDOA nQA1 QA1 GND VDD nc VDDA nc GND REF_CLK nOEA VDD 24 23 22 21 20 19 18 17 C11 C17 10uF 0.1uF 0.1uF 2 Ferrite Bead C13 C12 0.1uF VDD C14 10uF 0.1uF Figure 6. ICS841N254I Application Schematic Power supply filter recommendations are a general guideline to be used for reducing external noise from coupling into the devices. The filter performance is designed for wide range of noise frequencies. This low-pass filter starts to attenuate noise at approximately 10kHz. If a specific frequency noise component is known, such as switching power supply frequencies, it is recommended that component values be adjusted and if required, additional filtering be added. Additionally, ICS841N254AKI REVISION A APRIL 18, 2011 good general design practices for power plane voltage stability suggests adding bulk capacitances in the local area of all devices. The schematic example focuses on functional connections and is not configuration specific. Refer to the pin description and functional tables in the datasheet to ensure the logic control inputs are properly set. 17 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Power Considerations This section provides information on power dissipation and junction temperature for the ICS841N254I. Equations and example calculations are also provided. 1. Power Dissipation. The total power dissipation for the ICS841N254I is the sum of the core power plus the analog power plus the power dissipated in the load(s). The following is the power dissipation for VDD = 3.3V + 5% = 3.465V, which gives worst case results. NOTE: Please refer to Section 3 for details on calculating power dissipated in the load. • Power (core)MAX = VDD_MAX * (IDD_MAX + IDDA_MAX + IDDOA&B_MAX ) = 3.465V *(113mA + 30mA + 72mA) = 744.98mW • Power (HCSL_output)MAX = 44.5mW * 2 = 89.0mW Total Power_MAX = (3.465V, with all outputs switching) = 744.98mW + 89.0mW = 833.98mW 2. Junction Temperature. Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad, and directly affects the reliability of the device. The maximum recommended junction temperature is 125°C. Limiting the internal transistor junction temperature, Tj, to 125°C ensures that the bond wire and bond pad temperature remains below 125°C. The equation for Tj is as follows: Tj = θJA * Pd_total + TA Tj = Junction Temperature θJA = Junction-to-Ambient Thermal Resistance Pd_total = Total Device Power Dissipation (example calculation is in section 1 above) TA = Ambient Temperature In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance θJA must be used. Assuming no air flow and a multi-layer board, the appropriate value is 37.7°C/W per Table 7 below. Therefore, Tj for an ambient temperature of 85°C with all outputs switching is: 85°C + 0.834W * 37.7°C/W = 116.4°C. This is below the limit of 125°C. This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow and the type of board (multi-layer). Table 7. Thermal Resistance θJA for 32 Lead VFQFN, Forced Convection θJA Vs. Air Flow Meters per Second Multi-Layer PCB, JEDEC Standard Test Boards ICS841N254AKI REVISION A APRIL 18, 2011 0 1 2.5 37.7°C/W 32.9°C/W 29.5°C/W 18 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER 3. Calculations and Equations. The purpose of this section is to calculate power dissipation on the IC per HCSL output pair. HCSL output driver circuit and termination are shown in Figure 7. VDD IOUT = 17mA ➤ VOUT RREF = 475Ω ± 1% RL 50Ω IC Figure 7. HCSL Driver Circuit and Termination HCSL is a current steering output which sources a maximum of 17mA of current per output. To calculate worst case on-chip power dissipation, use the following equations which assume a 50Ω load to ground. The highest power dissipation occurs when VDD_MAX. Power = (VDD_MAX – VOUT) * IOUT, since VOUT – IOUT * RL = (VDD_MAX – IOUT * RL) * IOUT = (3.465V – 17mA * 50Ω) * 17mA Total Power Dissipation per output pair = 44.5mW ICS841N254AKI REVISION A APRIL 18, 2011 19 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Reliability Information Table 8. θJA vs. Air Flow Table for a 32-lead VFQFN θJA vs. Air Flow Meters per Second Multi-Layer PCB, JEDEC Standard Test Boards 0 1 2.5 37.7°C/W 32.9°C/W 29.5°C/W Transistor Count The transistor count for ICS841N254I is: 23,445 ICS841N254AKI REVISION A APRIL 18, 2011 20 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Package Outline and Package Dimensions Package Outline - K Suffix for 32 Lead VFQFN (Ref.) S eating Plan e N &N Even (N -1)x e (R ef.) A1 Ind ex Area A3 N To p View Anvil Anvil Singulation Singula tion or OR Sawn Singulation L N e (Ty p.) 2 If N & N 1 are Even 2 E2 (N -1)x e (Re f.) E2 2 b A (Ref.) D e N &N Odd Chamfer 4x 0.6 x 0.6 max OPTIONAL 0. 08 C Bottom View w/Type A ID D2 C Bottom View w/Type C ID 2 1 2 1 CHAMFER 4 Th er mal Ba se D2 2 N N-1 RADIUS 4 N N-1 There are 2 methods of indicating pin 1 corner at the back of the VFQFN package are: 1. Type A: Chamfer on the paddle (near pin 1) 2. Type C: Mouse bite on the paddle (near pin 1) Table 9. Package Dimensions NOTE: The following package mechanical drawing is a generic drawing that applies to any pin count VFQFN package. This drawing is not intended to convey the actual pin count or pin layout of this device. The pin count and pinout are shown on the front page. The package dimensions are in Table 9. JEDEC Variation: VHHD-2/-4 All Dimensions in Millimeters Symbol Minimum Nominal Maximum N 32 A 0.80 1.00 A1 0 0.05 A3 0.25 Ref. b 0.18 0.25 0.30 ND & NE 8 D&E 5.00 Basic D2 & E2 3.0 3.3 e 0.50 Basic L 0.30 0.40 0.50 Reference Document: JEDEC Publication 95, MO-220 ICS841N254AKI REVISION A APRIL 18, 2011 21 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Table 10. Ordering Information Part/Order Number 841N254AKI 841N254AKIT 841N254AKILF 841N254AKILFT Marking ICS41N254AI ICS1N254AI ICS1N254AIL ICS1N254AIL Package 32 Lead VFQFN 32 Lead VFQFN “Lead-Free” 32 Lead VFQFN “Lead-Free” 32 Lead VFQFN Shipping Packaging Tray 2500 Tape & Reel Tray 2500 Tape & Reel Temperature -40°C to 85°C -40°C to 85°C -40°C to 85°C -40°C to 85°C NOTE: Parts that are ordered with an “LF” suffix to the part number are the Pb-Free configuration and are RoHS compliant. While the information presented herein has been checked for both accuracy and reliability, Integrated Device Technology (IDT) assumes no responsibility for either its use or for the infringement of any patents or other rights of third parties, which would result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial and industrial applications. Any other applications, such as those requiring high reliability or other extraordinary environmental requirements are not recommended without ICS841N254AKI REVISION A APRIL 18, 2011 22 ©2011 Integrated Device Technology, Inc. ICS841N254I Data Sheet 6024 Silver Creek Valley Road San Jose, California 95138 FEMTOCLOCK® NG CRYSTAL-TO-LVDS/HCSL CLOCK SYNTHESIZER Sales 800-345-7015 (inside USA) +408-284-8200 (outside USA) Technical Support [email protected] +480-763-2056 Fax: 408-284-2775 www.IDT.com/go/contactIDT DISCLAIMER Integrated Device Technology, Inc. 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