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SY89841U
Precision LVDS Runt Pulse Eliminator 2:1 Multiplexer
General Description
The SY89841U is a low jitter LVDS, 2:1 input multiplexer (MUX) optimized for redundant source switchover applications. Unlike standard multiplexers, the SY89841U unique 2:1 Runt Pulse Eliminator (RPE) MUX prevents any short cycles or "runt" pulses during switchover. In addition, a unique Fail-safe Input protection prevents metastable conditions when the selected input clock fails to a DC voltage (voltage between the pins of the differential input drops below 100mV). The differential input includes Micrel's unique, 3-pin input termination architecture that allows customers to interface to any differential signal (AC- or DCcoupled) as small as 100mV (200mVpp) without any level shifting or termination resistor networks in the signal path. The outputs are 350mV, LVDS with fast rise/fall times guaranteed to be less than 150ps. The SY89841U operates from a 2.5V 5% supply and is guaranteed over the full industrial temperature range of -40C to +85C. The SY89841U is part of Micrel's high-speed, Precision Edge(R) product line. All support documentation can be found on Micrel's web site at: www.micrel.com.
Precision Edge(R)
Features
* Selects between two sources, and provides a glitch-free, stable LVDS output * Guaranteed AC performance over temperature and supply voltage: - wide operating frequency: 1kHz to >1.5GHz - <870ps In-to-Out tpd - <150ps tr/tf * Unique patent-pending input isolation design minimizes crosstalk * Fail-safe input prevents oscillations * Ultra-low jitter design: - <1psrms random jitter - <1psrms cycle-to-cycle jitter - <10pspp total jitter (clock) - <0.7psrms MUX crosstalk induced jitter * Unique patent-pending input termination and VT pin accepts DC-coupled and AC-coupled inputs (CML, PECL, LVDS) * 350mV LVDS output swing * 2.5V +5% power supply * -40C to +85C industrial temperature range * Available in 16-pin (3mm x 3mm) MLFTM package
Applications
* Redundant clock switchover * Fail-safe clock protection
Markets
* * * * LAN/WAN Enterprise servers ATE Test and measurement
Precision Edge is a registered trademark of Micrel, Inc. MicroLeadFrame and MLF are trademarks of Amkor Technology, Inc.
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SY89841U
Typical Application
Primary Clock From System IN0 50 VT0 50 /IN0 VREF-AC0 IN1 50 VT1 50 /IN1 VREF-AC1 SEL (LVTTL/CMOS)
2:1 MUX 0
Primary Clock Secondary Clock
MUX
SEL
Select Primary
Select Secondary
1
S
OUTPUT Runt pulse eliminated from output Switchover occurs
Secondary Clock From Local Oscillator
Runt Pulse Elimination Logic
Simplified Example Illustrating Runt Pulse Eliminator (RPE) Circuit when Primary Clock Fails
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SY89841U
Ordering Information(1)
Part Number Package Type MLF-16 MLF-16 Operating Range Industrial Industrial Package Marking Lead Finish NiPdAu Pb-Free NiPdAu Pb-Free
SY89841UMG SY89841UMGTR(2)
Notes:
841U with Pb-Free bar-line Indicator 841U with Pb-Free bar-line Indicator
1. Contact factory for die availability. Dice are guaranteed at TA = 25C, DC Electricals Only. 2. Tape and Reel.
Pin Configuration
VREF-AC1
14
VT1
16 /IN0 VREF-AC0 VT0 IN0 1 2 3 4 5
15
/IN1
13 12 11 10 9 VCC CAP SEL GND 8
IN1
6
7
VCC
Q
16-Pin MLFTM (MLF-16)
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3
VCC
/Q
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SY89841U
Pin Description
Pin Number 4, 1, 16, 13 Pin Name IN0, /IN0, IN1, /IN1 Pin Function Differential Inputs: These input pairs are the differential signal inputs to the device. These inputs accept AC- or DC-coupled signals as small as 100mV. Each pin of a pair internally terminates to a VT pin through 50 . Please refer to the "Input Interface Applications" section for more details. Reference Voltage: This output biases to VCC -1.2V. It is used for AC-coupling inputs IN and /IN. Connect VREF-AC directly to the corresponding VT pin. Bypass with 0.01F low ESR capacitor to VCC. Maximum sink/source current is 1.5mA. Due to the limited drive capability, the VREF-AC pin is only intended to drive its respective VT pin. See the "Input Interface Applications" section for more details. Input Termination Center-Tap: Each side of the differential input pair terminates to a VT pin. The VT0 and VT1 pins provide a center-tap to a termination network for maximum interface flexibility. See the "Input Interface Applications" section for more details. Positive Power Supply: Bypass with 0.1F//0.01F low ESR capacitors as close to the VCC pins as possible. Differential Outputs: This LVDS differential output is a logic function of the IN0, IN1, and SEL inputs. Please refer to the truth table below for details. This single-ended TTL/CMOS-compatible input selects the inputs to the multiplexer. Note that this input is internally connected to a 25k pull-up resistor and will default to logic HIGH state if left open. Ground: Ground and exposed pad must be connected to the same ground plane. Power-On Reset (POR) Initialization capacitor. When using the multiplexer with RPE capability, this pin is tied to a capacitor to VCC. The purpose is to ensure the internal RPE logic starts up in a known state. See "Power-On Reset (POR) Description" section for more details regarding capacitor selection. If this pin is tied directly to VCC, the RPE function will be disabled and the multiplexer will function as a normal multiplexer. The CAP pin should never be left open.
2, 14
VREF-AC0 VREF-AC1
3, 15
VT0, VT1
5, 8, 12 6, 7
VCC Q, /Q
10
SEL GND Exposed Pad
9
11
CAP
Truth Table
Inputs IN0 0 1 X X /IN0 1 0 X X IN1 X X 0 1 /IN1 X X 1 0 SEL 0 0 1 1 Outputs Q 0 1 0 1 /Q 1 0 1 0
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Absolute Maximum Ratings(1)
Supply Voltage (VCC)............................. -0.5V to +4.0V Input Voltage (VIN)..................................... -0.5V to VCC Termination Current Source or sink current on VT..................... 100mA Source or sink current on IN, /IN................ 50mA VREF-AC Source or sink current.............................. 2mA Lead Temperature (soldering, 20 sec.)............ +260C Storage Temperature (Ts) ...................-65C to 150C
Operating Ratings(2)
Supply Voltage (VCC) ....................+2.375V to +2.625V Ambient Temperature (TA) .................. -40C to +85C Package Thermal Resistance(3) MLFTM ( JA) Still-Air ........................................................ 60C/W MLFTM ( JB) Junction-to-Board ...................................... 33C/W
DC Electrical Characteristics(4)
TA = -40C to +85C, unless otherwise stated.
Symbol VCC ICC RIN RDIFF_IN VIH VIL VIN VDIFF_IN VIN_FSI VT_IN VREF-AC
Notes: 1. Permanent device damage may occur if absolute maximum ratings are exceeded. This is a stress rating only and functional operation is not implied at conditions other than those detailed in the operational sections of this data sheet. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2. The data sheet limits are not guaranteed if the device is operated beyond the operating ratings. 3. Package Thermal Resistance assumes exposed pad is soldered (or equivalent) to the devices most negative potential on the PCB. JB values are determined for a 4-layer board in still air unless otherwise stated. 4. The circuit is designed to meet the DC specifications shown in the above table after thermal equilibrium has been established. 5. VIN(max) is specified when VT is floating.
JA
Parameter Power Supply Power Supply Current Input Resistance (IN-to-VT) Differential Input Resistance (IN-to-/IN) Input High Voltage (IN, /IN) Input Low Voltage (IN, /IN) Input Voltage Swing (IN, /IN) Differential Input Voltage Swing |IN-/IN| Input Voltage Threshold that Triggers FSI IN-to-VT (IN, /IN) Output Reference Voltage
Condition No load, max VCC
Min 2.375
Typ 85
Max 2.625 120 55 110 VCC VIH-0.1 VCC
Units V mA
45 90 1.2 0 See Figure 1a. Note 5. See Figure 1b. 0.1 0.2
50 100
V V V V
30
100 1.28
mV V V
VCC-1.3
VCC-1.2
VCC-1.1
and
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SY89841U
LVDS Outputs DC Electrical Characteristics(7)
VCC = 2.5V 5%; RL = 100
Symbol VOCM VOCM VOUT VDIFF-OUT Parameter Output Common Mode Voltage Change in Common Mode Voltage Output Voltage Swing Differential Output Voltage Swing See Figure 1a. See Figure 1b.
across output pair or equivalent; TA = -40C to + 85C, unless otherwise stated.
Condition Min 1.125 -50 250 500 350 700 Typ Max 1.275 +50 Units V mV mV mV
LVTTL/CMOS DC Electrical Characteristics(7)
VCC = 2.5V 5%; TA = -40C to + 85C, unless otherwise stated.
Symbol VIH VIL IIH IIL
Note: 7. The circuit is designed to meet the DC specifications shown in the above table after thermal equilibrium has been established.
Parameter Input HIGH Voltage Input LOW Voltage Input HIGH Current Input LOW Current
Condition
Min 2.0
Typ
Max 0.8
Units V V A A
-125 -300
30
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SY89841U
AC Electrical Characteristics(8)
VCC = 2.5V 5%; RL = 100
Symbol fMAX tpd Parameter Maximum Operating Frequency Differential Propagation Delay In-to-Q In-to-Q SEL-to-Q SEL-to-Q tpd Tempco tSKEW tJitter Differential Propagation Delay Temperature Coefficient Part-to-Part Skew Random Jitter Cycle-to-Cycle Jitter Total Jitter (TJ) Crosstalk-Induced Jitter tr, tf
Notes: 8. High-frequency AC-parameters are guaranteed by design and characterization. 9. Propagation delay is measured with input tr, tf 300ps (20% to 80%) and VIL 800mV. 10. Part-to-part skew is defined for two parts with identical power supply voltages at the same temperature and with no skew of the edges at the respective inputs. 11. Random Jitter is measured with a K28.7 character pattern, measured at across output pair or equivalent; TA = -40C to + 85C, unless otherwise stated.
Condition Clock VIN = 100mV to 200mV(9) VIN = 200mV to 800mV(9) RPE enabled, see Timing Diagram RPE disabled (VIN = VCC/2) 550 115 Note 10 Note 11 Note 12 Note 13 Note 14 At full output swing. 30 70 200 1 1 10 0.7 150 Min 1.5 470 440 Typ 2.0 625 575 870 800 17 900 Max Units GHz ps ps cycles ps fs/oC ps ps(rms) ps(rms) ps(pp) ps(rms) ps
Output Rise/Fall Time (20% to 80%)
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SY89841U
Functional Description
RPE MUX and Fail-Safe Input The SY89841U is optimized for clock switchover applications where switching from one clock to another clock without runt pulses (short cycles) is required. It features two unique circuits:
RPE and FSI Functionality The basic operation of the RPE MUX and FSI functionality is described with the following four case descriptions. All descriptions are related to the true inputs and outputs. The primary (or selected) clock is called CLK1; the secondary (or alternate) clock is called CLK2. Due to the totally asynchronous relation of the IN and SEL signals and an additional internal protection against metastability, the number of pulses required for the operations described in cases 1-4 can vary within certain limits. Refer to "Timing Diagrams" section for detailed information. Case #1: Two Normal Clocks and RPE Enabled In this case, the frequency difference between the two running clocks, IN0 and IN1, must not be greater than 1.5:1. For example, if the IN0 clock is 500MHz, the IN1 clock must be within the range of 334MHz to 750MHz. If the SEL input changes state to select the alternate clock, the switchover from CLK1 to CLK2 will occur in three stages. * Stage 1: The output will continue to follow CLK1 for a limited number of pulses. * Stage 2: The output will remain LOW for a limited number of pulses of CLK2. * Stage 3: The output follows CLK2.
Runt-Pulse Eliminator (RPE) Circuit
The RPE MUX provides a "glitchless" switchover between two clocks and prevents any runt pulses from occurring during the switchover transition. The design of both clock inputs is identical (i.e., the switchover sequence and protection is symmetrical for both input pair, IN0 or IN1. Thus, either input pair may be defined as the primary input). If not required, the RPE function can be permanently disabled to allow the switchover between inputs to occur immediately. If the CAP pin is tied directly to VCC, the RPE function will be disabled and the multiplexer will function as a normal multiplexer.
Fail-Safe Input (FSI) Circuit
The FSI function provides protection against a selected input pair that drops below the minimum amplitude requirement. If the selected input pair drops sufficiently below the 100mV minimum singleended input amplitude limit (VIN), or 200mV differentially (Vdiff_IN), the output will latch to the last valid clock state.
Stage 1 CLK1
Stage 2
Stage 3
CLK2
SEL
Select CLK1
Select CLK2
OUTPUT
Runt pulse eliminated from output
3 to 5 falling edges of CLK1
4 to 5 falling edges of CLK2
Timing Diagram 1
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SY89841U
Case #2: Input Clock Failure: Switching from a selected clock stuck HIGH to a valid clock (RPE enabled). If CLK1 fails HIGH before the RPE MUX selects CLK2 (using the SEL pin), the switchover will occur in three stages.
* Stage 1: The output will remain HIGH for a limited number of pulses of CLK2. * Stage 2: The output will switch to LOW and then remain LOW for a limited number of falling edges of CLK2. * Stage 3: The output will follow CLK2.
Stage 1 CLK1
Stage 2
Stage 3
CLK2
SEL
Select CLK1
Select CLK2
OUTPUT
14 to 16 falling edges of CLK2 Runt pulse eliminated from output
Timing Diagram 2 Note: Output show extended clock cycle during switchover. Pulse width for both high and low of this cycle will always be greater than 50% of the CLK2 period.
Case #3: Input Clock Failure: Switching from a selected clock stuck Low to a valid clock (RPE enabled). If CLK1 fails LOW before the RPE MUX selects CLK2 (using the SEL pin), the switchover will occur in two stages.
* Stage 1: The output will remain LOW for a limited number of falling edges of CLK2. * Stage 2: The output will follow CLK2.
Stage 1 CLK1
Stage 2
CLK2
SEL
Select CLK1
Select CLK2
OUTPUT
13 to 17 falling edges of CLK2
Timing Diagram 3
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SY89841U
Case #4: Input Clock Failure: Switching from the selected clock input stuck in an undetermined state to a valid clock input (RPE enabled). If CLK1 fails to an undetermined state (e.g., amplitude falls below the 100mV (VIN) minimum single-ended input limit, or 200mV differentially) before the RPE MUX selects CLK2 (using the SEL pin), the switchover to the valid clock CLK2 will occur either following Case #2 or Case #3, depending upon the last valid state at the CLK1
If the selected input clock fails to a floating, static, or extremely low signal swing, including 0mV, the FSI function will eliminate any metastable condition and guarantee a stable output signal. No ringing and no undetermined state will occur at the output under these conditions. Please note that the FSI function will not prevent duty cycle distortions or runt pulses in case of a slowly deteriorating (but still toggling) input signal. Due to the FSI function, the propagation delay will depend on rise and fall time of the input signal and on its amplitude. Refer to "Typical Operating Characteristics" for detailed information.
CLK1
CLK2
SEL
Select CLK1
Select CLK2
OUTPUT
as in case #2 as in case #3
Timing Diagram 4
Power-On Reset (POR) Description
The SY89841U includes an internal power-on reset (POR) function to ensure the RPE logic starts-up in a known logic state once the power-supply voltage is stable. An external capacitor connected between VCC and the CAP pin (pin 11) controls the delay for the power-on reset function. The required capacitor value calculation is based upon the time the system power supply needs to power up to a minimum of 2.3V. The time constant for the internal power-on-reset must be greater than the time required for the power supply to ramp up to a minimum of 2.3V.
The following formula describes this relationship:
C(F)
t dPS (ms) 12(ms/F)
As an example, if the time required for the system power supply to power up past 2.3V is 12ms, then the required capacitor value on pin 11 would be:
C(F) C 1F
12ms 12(ms/F)
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SY89841U
Typical Operating Characteristics
VCC = 2.5, GND = 0V, VIN stated. 400mVpk, tr/tf 300ps, RL = 100 across output pair or equivalent; TA = 25C, unless otherwise
Functional Characteristics
VCC = 2.5, GND = 0V, VIN stated. 400mVpk, tr/tf 300ps, RL = 100 across output pair or equivalent; TA = 25C, unless otherwise
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SY89841U
Singled-Ended and Differential Swings
VIN,VOUT 350mV (typical)
VDIFF_IN, VDIFF_OUT 700mV (typical)
Figure 1a. Single-Ended Voltage Swing
Figure 1b. Differential Voltage Swing
Input Stage
VCC
IN 50 VT 50 /IN GND
Figure 2. Simplified Differential Input Stage
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Input Interface Applications
VCC
VCC
VCC
IN LVPECL /IN VCC GND 0.01F VT 19 VREF-AC GND NC
GND GND 0.01F LVPECL
IN /IN 50 50 VCC VT VREF-AC SY89841U
IN CML /IN SY89841U GND NC NC VT VREF-AC
SY89841U
Option: may connect VT to VCC Figure 3a. LVPECL Interface (DC-Coupled) Figure 3b. LVPECL Interface (AC-Coupled) Figure 3c. CML Interface (DC-Coupled)
VCC
VCC
IN CML /IN SY89841U GND VCC VT VREF-AC 0.01F
IN LVDS /IN SY89841U GND NC NC VT VREF-AC
Figure 3d. CML Interface (AC-Coupled)
Figure 3e. LVDS Interface (DC-Coupled)
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SY89841U
LVDS Output Interface Applications
49.9, 1% vOCM, vOCM
vOD vOH, vOL vOH, vOL
100
49.9, 1%
GND
Figure 4a. LVDS Differential Measurement
GND
Figure 4b. LVDS Common Mode Measurement
Related Product and Support Documentation
Part Number SY89840U SY89842U Function Precision LVPECL Runt Pulse Eliminator 2 :1 Multiplexer Precision CML Runt Pulse Eliminator 2 :1 Multiplexer MLFTM Application Note HBW Solutions New Products and Applications Data Sheet Link www.micrel.com/product-info/products/sy89840u.shtml. www.micrel.com/product-info/products/sy89842u.shtml. www.amkor.com/products/notes_papers/MLFAppNote.pdf www.micrel.com/product-info/products/solutions.shtml
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16 Lead MicroLeadFrameTM (MLF-16)
Packages Notes: 1. Package meets Level 2 Moisture Sensitivity Classification. 2. All parts are dry-packed before shipment. 3. Exposed pad must be soldered to a ground for proper thermal management.
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2005 Micrel, Incorporated.
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