SY89843U
Precision LVPECL Runt Pulse Eliminator 2:1
MUX with 1:2 Fanout and Internal Termination
General Description
The SY89843U is a low jitter PECL, 2:1 differential input
multiplexer (MUX) optimized for redundant source
switchover applications. Unlike standard multiplexers,
the SY89843U 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 DC-coupled)
as small as 100mV (200mV
PP
) without any level shifting
or termination resistor networks in the signal path. The
output is 800mV, 100K compatible LVPECL with fast
rise/fall times guaranteed to be less than 190ps.
The SY89843U operates from a 2.5V ±5% or 3.3V
±10% supply and is guaranteed over the full industrial
temperature range of –40°C to +85°C. The SY89843U is
®
part of Micrel’s high-speed, Precision Edge product
line. All support documentation can be found on Micrel’s
web site at:
www.micrel.com.
Precision Edge
®
Features
Selects between two sources, and provides a
glitch-free, stable LVPECL output
Guaranteed AC performance over temperature
and supply voltage:
– Wide operating frequency: 1kHz to >1.5GHz
– < 880ps In-to-Out t
pd
– < 190ps t
r
/t
f
Unique patent-pending input isolation design
minimizes crosstalk
Fail-Safe Input prevents oscillations
Ultra-low jitter design:
– 65fs RMS phase jitter (Type)
– 0.7ps
RMS
MUX crosstalk induced jitter
Unique patent-pending input termination and VT
pin accepts DC- and AC-coupled inputs (CML,
PECL, LVDS)
800mV LVPECL output swing
2.5V ±5% or 3.3V ±10% supply voltage
–40°C to +85°C industrial temperature range
Available in 24-pin (4mm x 4mm) QFN package
Applications
Redundant clock switchover
Failsafe clock protection
Markets
LAN/WAN
Enterprise servers
ATE
Test and measurement
Precision Edge is a registered trademark of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
Oct. 1, 2013
M9999-052207-B
hbwhelp@micrel.com
or (408) 955-1690
Micrel, Inc.
SY89843U
Typical Application
Simplified Example Illustrating RPE (Runt Pulse Elimination)
Circuit when Primary Clock Fails
Oct. 1, 2013
2
M9999-052207-B
hbwhelp@micrel.com
or (408) 955-1690
Micrel, Inc.
SY89843U
Ordering Information
(1)
Part Number
SY89843UMG
SY89843UMGTR
Notes:
1. Contact factory for die availability. Dice are guaranteed at T
A
= 25°C, DC Electricals Only.
2. Tape and Reel.
(2)
Package Type
QFN-24
QFN-24
Operating Range
Industrial
Industrial
Package Marking
843U with bar-line
Pb-Free indicator
843U with bar-line
Pb-Free indicator
Lead Finish
NiPdAu
Pb-Free
NiPdAu
Pb-Free
Pin Configuration
24-Pin QFN
Oct. 1, 2013
3
M9999-052207-B
hbwhelp@micrel.com
or (408) 955-1690
Micrel, Inc.
SY89843U
Pin Description
Pin Number
5, 2
23, 20
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
(200mV
PP
). Each pin of a pair internally terminates to a VT pin through 50Ω.
Please refer to 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. Please refer to the “Input Interface Applications”
section for more details.
Reference Voltage: These outputs bias to V
CC
–1.2V. They are used for AC-
coupling inputs IN and /IN. Connect VREF-AC directly to the corresponding VT
pin. Bypass with 0.01µF low ESR capacitor to VCC. Maximum sink/source current
is ±1.5mA. Please refer to the “Input Interface Applications” section for more
details.
This single-ended TTL/CMOS-compatible input selects the inputs to the
multiplexer. Note that this input is internally connected to a 25kΩ pull-up resistor
and will default to logic HIGH state if left open.
Positive Power Supply: Bypass with 0.1µF//0.01µF low ESR capacitors as close
to VCC pins as possible.
Differential Outputs: These differential LVPECL outputs are a logic function of the
IN0, IN1, and SEL inputs. Please refer to the truth table below for details.
Ground: Ground pin and exposed pad must be connected to the same ground
plane.
Power-On Reset (POR) Initialization capacitor. When using the multiplexer with
RPE capability, the 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.
4, 22
VT0, VT1
3, 21
VREF-AC0
VREF-AC1
15
1, 6, 9, 10,
13, 19, 24
7, 8
11, 12
14, 17, 18
SEL
VCC
Q0, /Q0
Q1, /Q1
GND
Exposed Pad
16
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
Oct. 1, 2013
4
M9999-052207-B
hbwhelp@micrel.com
or (408) 955-1690
Micrel, Inc.
SY89843U
Absolute Maximum Ratings
(1)
Supply Voltage (V
CC
) .............................................. –0.5V to +4.0V
Input Voltage (V
IN
) ......................................................–0.5V to V
CC
LVPECL Output Current (I
OUT
)
Continuous .................................................................. ±50mA
Surge ........................................................................ ±100mA
Termination Current
Source/Sink Current on V
T
........................................ ±100mA
Input Current
Source/sink current on IN, /IN ..................................... ±50mA
V
REF-AC
Current
Source/sink current on V
REF-AC
...................................... ±2mA
Lead Temperature (soldering, 20 sec.) ..............................+260°C
Storage Temperature (Ts) .................................... –65°C to 150
°C
Operating Ratings
(2)
Supply Voltage (V
CC
) .............................+2.375V to +2.625V
...............................................................+3.0V to +3.6V
Ambient Temperature (T
A
) ........................... –40°C to +85°C
(3)
Package Thermal Resistance
QFN (
JA
)
Still-Air ............................................................... 50°C/W
QFN (
JB
)
Junction-to-Board .............................................. 30°C/W
DC Electrical Characteristics
(4)
T
A
= –40°C to +85°C; unless otherwise stated.
Symbol
V
CC
I
CC
R
IN
R
DIFF_IN
V
IH
V
IL
V
IN
V
DIFF_IN
V
IN_FSI
V
T_IN
V
REF-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.
JA
and
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. V
IN
(max) is specified when V
T
is floating.
Parameter
Power Supply
Power Supply Current
Input Resistance
(IN-to-V
T
)
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-V
T
(IN, /IN)
Output Reference Voltage
Condition
Min
2.375
3.0
Typ
2.5
3.3
70
50
100
Max
2.625
3.6
100
55
110
V
CC
V
IH
–0.1
V
CC
Units
V
V
mA
Ω
Ω
V
V
V
V
No load, max V
CC
.
45
90
1.2
0
See Figure 1a. Note 5
See Figure 1b.
0.1
0.2
30
100
1.28
mV
V
V
V
CC
–1.3
V
CC
–1.2
V
CC
–1.1
Oct. 1, 2013
5
M9999-052207-B
hbwhelp@micrel.com
or (408) 955-1690
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