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CY23FS04
FailsafeTM 2.5V/ 3.3V Zero Delay Buffer
Features
* Internal DCXO for continuous glitch-free operation * Zero input-output propagation delay * Low-jitter (< 35 ps RMS) outputs * Low Output-to-Output skew (< 200 ps) * 4.17 MHz-170 MHz reference input * Supports industry standard input crystals * 170 MHz outputs * 5V-tolerant inputs * Phase-locked loop (PLL) Bypass Mode * Dual Reference Inputs * 16-pin TSSOP * 2.5V or 3.3V output power supplies * 3.3V core power supply * Industrial temperature available
Functional Description
The CY23FS04 is a FailSafe zero delay buffer with two reference clock inputs and four phase-aligned outputs. The device provides an optimum solution for applications where continuous operation is required in the event of a primary clock failure. The continuous, glitch-free operation is achieved by using a DCXO, which serves as a redundant clock source in the event of a reference clock failure by maintaining the last frequency and phase information of the reference clock. The unique feature of the CY23FS04 is that the DCXO is in fact the primary clocking source, which is synchronized (phase-aligned) to the external reference clock. When this external clock is restored, the DCXO automatically resynchronizes to the external clock. The frequency of the crystal, which will be connected to the DCXO must be chosen to be an integer factor of the frequency of the reference clock. This factor is set by two select lines: S[2:1], please see Table 1. Output power supply, VDD can be connected to either 2.5V or 3.3V. VDDC is the power supply pin for internal circuits and must be connected to 3.3V.
Block Diagram
Pin Configuration
XIN XOUT REFSEL DCXO REF1 REF2 FBK FailsafeTM Block PLL
REF1 REF2 CLKB1 CLKB2 S2
2 2
CLKA[1:2] CLKB[1:2]
VSS VDDC XIN
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
REFSEL FBK CLKA1 CLKA2 S1 VDD FAIL#/SAFE XOUT
16 pin TSSOP
Decoder FAIL# /SAFE 2
CY23FS04
S[2:1]
Cypress Semiconductor Corporation Document #: 38-07304 Rev. *B
*
3901 North First Street
*
San Jose, CA 95134 * 408-943-2600 Revised October 12, 2004
CY23FS04
Pin Definition
Pin Number 1,2 3,4 14,13 15 12,5 8 9 10 11 7 6 16 Pin Name REF[1:2] CLKB[1:2] CLKA[1:2] FBK S[1:2] XIN XOUT FAIL#/SAFE VDD VDDC VSS REFSEL Reference clock inputs. Bank B clock outputs.[1,2] Bank A clock outputs.[1,2] Feedback input to the PLL.[1,4] Frequency select pins and PLL and DCXO bypass mode.[3] Reference crystal input. Reference crystal output. Valid reference indicator. A high level indicates a valid reference input. 2.5V or 3.3V power supply. 3.3V power supply. Ground. Reference select. Selects the active reference clock from either REF1 or REF2. REFSEL = 1, REF1 is selected, REFSEL = 0, REF2 is selected. Description 5V-tolerant[4] .
Table 1. Configuration Table XTAL (MHz) S[2:1] 00 01 10 11 8.33 8.00 8.33 30.00 25.00 28.33 4.17 16.00 50.00 15.00 50.00 170.00 4.17 16.00 50.00 Min. Max. REF (MHz) Min. Max. OUT (MHz) Min. Max. 15.00 50.00 170.00 REF:OUT ratio x1 x1 x1 PLL and DCXO Bypass Mode 1/2 2 6 1/2 2 6 REF:XTAL ratio Out:XTAL ratio
FailSafe Function
The CY23FS04 is targeted at clock distribution applications that could or which currently require continued operation should the main reference clock fail. Existing approaches to this requirement have utilized multiple reference clocks with either internal or external methods for switching between references. The problem with this technique is that it leads to interruptions (or glitches) when transitioning from one reference to another, often requiring complex external circuitry or software to maintain system stability. The technique implemented in this design completely eliminates any switching of references to the PLL, greatly simplifying system design. The CY23FS04 PLL is driven by the crystal oscillator, which is phase-aligned to an external reference clock so that the output of the device is effectively phase-aligned to reference via the external feedback loop. This is accomplished by utilizing a digitally controlled capacitor array to pull the crystal frequency over an approximate range of +300 ppm from its nominal frequency.
REF OUT F a il# /S a fe
tF S L
tF S H
Figure 1. Fail#/Safe Timing for Input Reference Failing Catastrophically
Notes: 1. For normal operation, connect either one of the four clock outputs to the FBK input. 2. Weak pull-downs on all outputs 3. Weak pull-ups on these inputs. 4. Weak pull-down on these inputs.
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CY23FS04
t F S L (m a x )
= 2 ( tR E F x n ) + 25ns F REF n= ( in a b o v e e x a m p le ) F XTAL = 4
t F S H ( m in ) =
12(
tR E F x n
)
+
25ns
Figure 2. Fail#/Safe Timing Formula
Table 2. FailSafe Timing Table Parameter tFSL tFSH Description Fail#/Safe Assert Delay Fail#/Safe De-assert Delay Conditions Measured at 80% to 20%, Load = 15 pF Measured at 80% to 20%, Load = 15 pF See Figure 2 Min. Max. See Figure 2 Unit ns ns
In this mode, should the reference frequency fail (i.e. stop or disappear), the DCXO maintains its last setting and a flag signal (FAIL#/SAFE) is set to indicate failure of the reference clock. The CY23FS04 provides 2 select bits, S1 through S2 to control the reference to crystal frequency ratio. The DCXO is internally tuned to the phase and frequency of the external reference
only when the reference frequency divided by this ratio is within the DCXO capture range. If the frequency is out of range, a flag will be set on the FAIL#/SAFE pin notifying the system that the selected reference is not valid. If the reference moves in range, then the flag will be cleared, indicating to the system that the selected reference is valid.
Reference + 300 ppm Reference Reference - 300 ppm Reference Off Frequency
Output + 300 ppm Output Output - 300 ppm
Fail#/Safe Volt
tFSH tFSL Time
Figure 3. FailSafe Timing Diagram: Input Reference Slowly Drifting Out of FailSafe Capture Range
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CY23FS04
Failsafe typical frequency settling time
Initial valid Ref1=20MHz +100ppm, then switching to REF2=20MHz OUTPUT FREQUENCY DELTA (ppm)
150
100
50
0 0 0.45 1.3
SETTLING TIME (ms)
2.5
Figure 4. FailSafe Reference Switching Behavior
Figure 5. FailSafe Effective Loop Bandwidth (min)
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CY23FS04
REF1
REF2
REFSEL 0 ms
0 d eg
-1 8 0 d e g
0 ms 1 .4 m s
Figure 6. Sample Timing of Muxing Between Two Reference Clocks 180C Out of Phase and Resulting Output Phase Offset Typical Settling Time (105 MHz)
190 fs/cy 0 0 ms 1.4 ms
190 fsec/cycle = 0.125 mradian/cycle
Figure 7. Resulting Output dphase/Cycle Typical Rate of Change (105 MHz)
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CY23FS04
D u ty C y c le - t D C V D D /2 V D D /2 t1 t2 S le w R a te - t (S R ) 80% 20% t S R (O ) O u tp u t-O u tp u t S k e w - t S K (O ) V D D /2 t S R (O ) 80% 20% 0V V DD V D D /2 V DD 0V
V D D /2 t S K (O ) P a rt to P a rt S k e w - t S K (P P ) FBK, P a rt 1 FBK, P a rt 2 V D D /2
V D D /2 t S K (P P )
S ta tic P h a s e O ffs e t - t ( ) REF V D D /2
FBK
V D D /2 t ( )
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CY23FS04
XTAL Selection Criteria and Application Example Choosing the appropriate XTAL will ensure the FailSafe device will be able to span an appropriate frequency of operation. Also, the XTAL parameters will determine the holdover frequency stability. Critical parameters are as follows. Our recommendation is to choose: * Low C0/C1 ratio (240 or less) so that the XTAL has enough range of pullability. * Low temperature frequency variation * Low manufacturing frequency tolerance * Low aging. C0 is the XTAL shunt capacitance (3 pF - 7 pF typ). Example:[5] C1 is the XTAL motional capacitance (10 fF - 30 fF typ). The capacitive load as "seen" by the XTAL is across its terminals. It is named Clmin (for minimum value), and Clmax (for maximum value).These are used for calculating the pull range. Please note that the Cl range "center" is approximately 20 pF, but we may not want a XTAL calibrated to that load. This is because the pullability is not linear, as represented in the equation above. Plotting the pullability of the XTAL shows this expected behavior as shown in Figure 8. In this example, specifying a XTAL calibrated to 14 pF load provides a balanced ppm pullability range around the nominal frequency.
Clmin = (12 pF IC input cap + 0 pF pulling cap+ 6 pF trace cap on board)/2 = 9 pF Clmax = (12 pF IC input cap + 48 pF pulling cap+ 6 pF trace cap on board)/2 = 33 pF Pull Range =(fClmin-fClmax)/fClmin = ((C1)/2)[(1/(C0+Clmin))-(1/(C0+Clmax))] Pull Range in ppm = ((C1)/2)[(1/(C0+Clmin))-(1/(C0+Clmax))] x 106
Note: 5. The above example shows the maximum range the FailSafe internal capacitor array is capable of (0 to 48.6 pF).Cypress recommends the min/max capacitor array values be programmed to a narrower range such as 6 pF-30 pF, or 7.5 pF-27 pF. This ensures the XTAL operates between series resonance and anti-resonance. Please contact Cypress for choosing these range settings.
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CY23FS04
Pullability Range Vs. Cload
(Normalized to 14pF Cload) 400.00
Delta Freq. from nom
300.00 200.00 100.00 0.00 -100.00 -200.00 -300.00 -400.00 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
Cload (pF)
C0/C1 = 200 C0/C1 = 300 C0/C1 = 400
Figure 8. Frequency vs. Cload Behavior for Example XTAL Table 3. Pullability Range fro XTAL with Different C0/C1 Ratio C0/C1 Ratio 200 300 400 Cload(min.) 8.0 8.0 8.0 Cload(max.) 32.0 32.0 32.0 Pullability Range -385 -256 -192 333 222 166 Calculating the capture range involves subtracting error tolerances as follows: Parameter ........................................................ f error (ppm) Manufacturing frequency tolerance ...................................15 Temperature stability ..........................................................30 Aging ................................................................................... 3 Board / trace variation ......................................................... 5 Total ....................................................................................53 Example: Capture Range for XTAL with C0/C1 Ratio of 200 Negative Capture Range= -385 ppm + 53 ppm = -332 ppm Positive Capture Range = 333 ppm - 53 ppm = +280 ppm It is important to note that the XTAL with lower C0/C1 ratio has wider pullability/capture range as compared to the higher C0/C1 ratio. This will help the user in selecting the appropriate XTAL for use in the FailSafe application.
Calculated value of the pullability range for the XTAL with C0/C1 ratio of 200, 300 and 400 are shown in Table 3. For this calculation Cl(min) = 8 pF and Cl(max)= 32 pF has been used. Using a XTAL that has a nominal frequency specified at load capacitance of 14 pF, almost symmetrical pullability range has been obtained. Next, it is important to calculate the pullability range including error tolerances. This would be the capture range of the input reference frequency that the FailSafe device and XTAL combination would reliably span.
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CY23FS04
Absolute Maximum Conditions
Parameter VDD VIN TS TA TJ ESDHBM OJC OJA UL-94 MSL Input Voltage Temperature, Storage Temperature, Operating Ambient Temperature, Junction ESD Protection (Human Body Model) Dissipation, Junction to Case Dissipation, Junction to Ambient Flammability Rating Moisture Sensitivity Level Description Supply Voltage Relative to VSS Non Functional Commercial Grade Industrial Grade Functional MIL-STD-883, Method 3015 Mil-Spec 883E Method 1012.1 JEDEC (JESD 51) At 1/8 in. 2000 29.87 120.11 V-0 1 Condition Min. -0.5 -0.5 -65 0 -40 Max. 4.6 VDD+0.5 +150 70 85 125 Unit V VDC C C C C V C/W C/W
Multiple Supplies: The Voltage on any input or I/O pin cannot exceed the power pin during power-up. Power supply sequencing is NOT required.
Recommended Pullable Crystal Specifications[6]
Parameter FNOM CLNOM R1 R3/R1 DL F3SEPLI F3SEPLO C0 C0/C1 C1 Name Nominal crystal frequency Nominal load capacitance Equivalent series resistance (ESR) Ratio of third overtone mode ESR to fundamental mode ESR Crystal drive level Fundamental mode Ratio used because typical R1 values are much less than the maximum spec No external series resistor assumed Comments Parallel resonance, fundamental mode, AT cut Min. 8.00 - - 3 - 300 - - 180 14.4 Typ. - 14 - - 0.5 - - - - 18 Max. 30.00 - 25 - 2 - -150 7 250 21.6 fF mW ppm ppm pF Unit MHz pF
Third overtone separation from 3*FNOM High side Third overtone separation from 3*FNOM Low side Crystal shunt capacitance Ratio of shunt to motional capacitance Crystal motional capacitance
Table 4. Operating Conditions for FailSafe Commercial/Industrial Temperature Devices Parameter VDDC VDD TA CL CIN CXIN TPU 3.3V Supply Voltage 2.5V Supply Voltage Range 3.3V Supply Voltage Range Ambient Operating Temperature, Commercial Ambient Operating Temperature, Industrial Output Load Capacitance (Fout < 100 MHz) Output Load Capacitance (Fout > 100 MHz) Input Capacitance (except XIN) Crystal Input Capacitance (all internal caps off) Power-up time for all VDDs to reach minimum specified voltage (power ramps must be monotonic) 10 0.05 Description Min. 3.135 2.375 3.135 0 -40 Max. 3.465 2.625 3.465 70 85 30 15 7 13 500 Unit V V V C C pF pF pF pF ms
Note: 6. Ecliptek ECX-5788-13.500M, ECX-5807-19.440M, ECX-5872-19.53125M, ECX-5806-18.432M, ECX-5808-27.000M, ECX-5884-17.664M, ECX-5883-16.384M,ECX-5882-19.200M,ECX-5880-24.576M meet these specifications.
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CY23FS04
Table 5. Electrical Characteristics for FailSafe Commercial/Industrial Temperature Devices Parameter VIL VIH IIL IIH IOL IOH IDDQ Description Input Low Voltage Input High Voltage Input Low Current Input High Current Output Low Current Output High Current Quiescent Current Test Conditions CMOS Levels, 30% of VDD CMOS Levels, 70% of VDD VIN = VSS (100k pull-up only) VIN = VDD (100k pull-down only) VOL = 0.5V, VDD = 2.5V VOL = 0.5V, VDD = 3.3V VOH = VDD - 0.5V, VDD = 2.5V VOH = VDD - 0.5V, VDD = 3.3V All inputs grounded, PLL and DCXO in bypass mode, Reference Input = 0 18 20 18 20 250 0.7 x VDD 50 50 Min. Typ. Max. 0.3 x VDD Unit V V A A mA mA mA mA A
Table 6. Switching Characteristics for FailSafe Commercial/Industrial Temperature Devices Parameter[8] fREF fOUT fXIN tDC tSR(I) tSR(O) Description Reference Frequency Output Frequency DCXO Frequency Duty Cycle Input Slew Rate Output Slew Rate Measured at VDD/2 Measured on REF1 Input, 30% to 70% of VDD Measured from 20% to 80% of VDD = 3.3V, 15 pF Load Measured from 20% to 80% of VDD = 2.5V, 15 pF Load tSK(O) tSK(PP) t()[7] tD()[7] tJ(CC) Output to Output Skew Part to Part Skew Static Phase Offset Dynamic Phase Offset Cycle-to-cycle Jitter All outputs equally loaded, measured at VDD/2 Measured at VDD/2 Measured at VDD/2 Measured at VDD/2 Load = 15 pF, fOUT 6.25 MHz Test Conditions Commercial/Industrial Grades 15-pF Load, Commercial/Industrial Grades Min. 4.17 4.17 8.0 47 0.5 0.8 0.4 Max. 170 170 30 53 4.0 4.0 3.0 200 500 250 200 200 35 Unit MHz MHz MHz % V/ns V/ns V/ns ps ps ps ps ps psRMS
Ordering Information
Part Number CY23FS04ZI CY23FS04ZIT CY23FS04ZC CY23FS04ZCT Package Type 16-Pin TSSOP 16-Pin TSSOP - Tape and Reel 16-Pin TSSOP 16-Pin TSSOP - Tape and Reel Product Flow Industrial, -40C to 85C Industrial, -40C to 85C Commercial, 0C to 70C Commercial, 0C to 70C
Notes: 7. The t() reference feedback input delay is guaranteed for a maximum 4:1 input edge ratio between the two signals as long as tSR(I) is maintained. 8. Parameters guaranteed by design and characterization, not 100% tested in production. 9. Includes typical board trace capacitance of 6-7pF each XIN, XOUT.
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CY23FS04
Package Drawing and Dimensions
16-lead TSSOP 4.40 MM Body Z16.173
PIN 1 ID
1
DIMENSIONS IN MM[INCHES] MIN. MAX. REFERENCE JEDEC MO-153
6.25[0.246] 6.50[0.256] 4.30[0.169] 4.50[0.177]
PACKAGE WEIGHT 0.05 gms PART # Z16.173 STANDARD PKG. ZZ16.173 LEAD FREE PKG.
16
0.65[0.025] BSC.
0.19[0.007] 0.30[0.012]
1.10[0.043] MAX.
0.25[0.010] BSC GAUGE PLANE 0-8
0.076[0.003] 0.85[0.033] 0.95[0.037] 0.05[0.002] 0.15[0.006] SEATING PLANE 0.50[0.020] 0.70[0.027] 0.09[[0.003] 0.20[0.008]
4.90[0.193] 5.10[0.200]
51-85091-*A
FailSafe is a trademark of Cypress Semiconductor. All product and company names mentioned in this document are the trademarks of their respective holders.
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(c) Cypress Semiconductor Corporation, 2004. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
CY23FS04
Document History Page
Document Title: CY23FS04 FailsafeTM 2.5V/ 3.3V Zero Delay Buffer Document #: 38-07304 Rev. *B REV. ** *A *B ECN NO. Issue Date 123698 223811 276712 04/24/03 See ECN See ECN Orig. of Change RGL RGL New data sheet Removed (TLOCK)Lock Time Specification Description of Change
RGL/ZJX Changed the XTAL Specifications table.
Document #: 38-07304 Rev. *B
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