EXAR XRK7933

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XRK7933
PRELIMINARY
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
MARCH 2005
REV. P1.0.1
GENERAL DESCRIPTION
The XRK7933 is a PLL clock driver designed
specifically for redundant clock tree designs. The
device receives two differential LVPECL clock signals
from which it generates 5 new differential LVPECL
clock outputs. Two of the output pairs regenerate the
input signals frequency and phase while the other
three pairs generate 3x, phase aligned clock outputs.
External PLL feedback is used to also provide zero
delay buffer performance.
The XRK7933 Intelligent Dynamic Clock Switch
circuit continuously monitors both input CLK signals.
Upon detection of a failure (CLK stuck HIGH or LOW
for at least 1 period), the INP_BAD for that CLK will
be latched (H). If that CLK is the primary clock, the
device will switch to the good secondary clock and
phase/frequency alignment will occur with minimal
output phase disturbance. The typical phase bump
caused by a failed clock is eliminated.
FEATURES
• Fully Integrated PLL
• Intelligent Dynamic Clock Switch
• LVPECL Clock Outputs
• LVCMOS Control I/O
• 3.3V Operation
• 32-Lead LQFP Packaging
FIGURE 1. BLOCK DIAGRAM OF THE XRK7933
CLK_Selected
INP1Bad
INP0Bad
Man_Override
Alarm_Reset
Sel_CLK
Dynamic
Switch
Logic
PLL_En
Qb0
Qb0
Qb1
Qb1
OR
CLK0
CLK0
CLK1
CLK1
Ext_FB
Ext_FB
MR
÷4
PLL
200-400MHz
÷12
Qb2
Qb2
Qa0
Qa0
Qa1
Qa1
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com
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PRELIMINARY
XRK7933
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
REV. P1.0.1
PRODUCT ORDERING INFORMATION
PRODUCT NUMBER
PACKAGE TYPE
OPERATING TEMPERATURE RANGE
XRK7933
32-Lead LQFP
-40°C to +85°C
VCC
Qb0
Qb0
Qb1
Qb1
Qb2
Qb2
VCC
24
23
22
21
20
19
18
17
FIGURE 2. PIN OUT OF THE XRK7933
Qa1
25
16
VCC
Qa1
26
15
Inp0bad
Qa0
27
14
Inp1bad
Qa0
28
13
CK_Selected
VCC
29
12
GND
VCC_PLL
30
11
Ext_FB
Man_Override
31
10
Ext_FB
PLL_En
32
9
2
8
GND
7
CLK1
6
CLK1
5
Sel_CLK
4
CLK0
3
CLK0
2
Alarm_Reset
MR
1
XRK7933
GND
XRK7933
PRELIMINARY
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
xr
REV. P1.0.1
PIN DESCRIPTIONS
PIN NAME
TYPE
DESCRIPTION
CLK0, CLK0
CLK1, CLK1
LVPECL Input
LVPECL Input
Differential PLL clock reference (CLK0 pulldown, CLK0 pullup)
Differential PLL clock reference (CLK1 pulldown, CLK1 pullup)
Ext_FB, Ext_FB
LVPECL Input
Differential PLL feedback clock (Ext_FB pulldown, Ext_FB pullup)
Qa[1:0], Qa[1:0]
LVPECL Output
Differential 1x output pairs
Qb[2:0], Qb[2:0]
LVPECL Output
Differential 3x output pairs
Inp0bad
LVCMOS Output
Indicates detection of a bad input reference clock 0 with respect to the feedback signal. The output is active HIGH and will remain HIGH until the alarm
reset is asserted.
Inp1bad
LVCMOS Output
Indicates detection of a bad input reference clock 1 with respect to the feedback signal. The output is active HIGH and will remain HIGH until the alarm
reset is asserted.
Clk_Selected
LVCMOS Output
0 - if clock 0 is selected
1 - if clock 1 is selected
Alarm_Reset
LVCMOS Input
0 - will reset the input bad flags and align Clk_Selected with Sel_Clk. The input
is one-shotted (50KΩ pullup).
Sel_Clk
LVCMOS Input
0 - selects CLK0
1 - selects CLK1 (40kΩ pulldown)
Manual_Override
LVCMOS Input
1 - disables internal clock switch circuitry (40KΩ pulldown).
PLL_En
LVCMOS Input
0 - bypasses selected input reference around the phase-locked loop (50KΩ
pullup).
MR
LVCMOS Input
0 - resets the internal dividers forcing Q outputs LOW. Asynchronous to the
clock (50KΩ pullup).
VCCA
Power Supply
PLL power supply
VCC
Power Supply
Digital power supply
GNDA
Power Supply
PLL Ground
GND
Power Supply
Digital Ground
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PRELIMINARY
XRK7933
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
REV. P1.0.1
ABSOLUTE MAXIMUM RATINGSa
SYMBOL
CHARACTERISTICS
MIN
MAX
UNIT
VCC
Supply Voltage
-0.3
3.6
V
VIN
DC Input Voltage
-0.3
VCC+0.3
V
DC Output Voltage
-0.3
VCC+0.3
V
DC Input Current
+20
mA
DC Output Current
+50
mA
125
°C
VOUT
IIN
IOUT
TS
Storage Temperature
-65
CONDITION
a. Absolute maximum continuous ratings are those maximum values beyond which damage to the device may occur.
Exposure to these conditions or conditions beyond those indicated may adversely affect device reliability. Functional
operation at absolute-maximum-rated conditions is not implied.
GENERAL SPECIFICATIONS
SYMBOL
CHARACTERISTICS
MIN
TYP
MAX
VCC-2
UNIT
VTT
Output termination voltage
MM
ESD Protection (Machine model)
200
V
HBM
ESD Protection (Human body model)
2000
V
LU
Latch-up immunity
200
mA
CIN
Input Capacitance
θJA
Thermal resistance junction to ambient
JESD 51-3, single layer test board
V
4.0
pF
Inputs
62.0
°C/W
Natural convection
47.0
°C/W
Natural convection
Thermal resistance junction to case
14
°C/W
Operating junction temperature
115
°C
JESD 51-6, 2S2P multilayer test board
θJC
CONDITION
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XRK7933
PRELIMINARY
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
REV. P1.0.1
DC CHARACTERISTICS (VCC= 3.3 + 5%, TA= -40°C TO +85°C)
SYMBOL
CHARACTERISTICS
MIN
TYP
MAX
UNIT
VCC+0.3
V
0.8
V
-150
µΑ
CONDITION
LVCMOS control inputs (MR, PLL_En, Sel_CLK, Man_Override, Alarm_Reset)
VIH
Input voltage high
VIL
Input voltage low
IIN
Input currenta
2.0
100
VIN =VCC or VIN =GND
LVCMOS Control Outputs
VOH
Output High Voltage
VOL
Output Low Voltage
2.0
V
IOH=-10mA
0.55
V
IOL=10mA
+100
µΑ
VIN =VCC or VIN =GND
LVPECL clock inputs (CLK, CLK)b
IIN
Input current
LVPECL clock outputs (Qa[1:0], Qa[1:0], Qb[2:0], Qb[2:0])
VOH
Output high voltage
VCC-1.2
VCC-0.7
V
Termination 50Ω to VTT
VOL
Output low voltage
VCC-1.9
VCC-1.45
V
Termination 50Ω to VTT
Supply Current
IGND
Maximum ground supply current - gnd pins
180
mA
GND pins
ICCPLL
Maximum PLL power supply - VCC_PLL pin
15
mA
VCCPLL pin
a. Inputs have internal pullup/pulldown resistors which affect the input current.
b. Clock inputs driven by LVPECL compatible signals.
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PRELIMINARY
XRK7933
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
REV. P1.0.1
AC CHARACTERISTICS (VCC= 3.3 + 5%, TA= -40°C TO +85°C) (NOTE 5)
SYMBOL
fref
PARAMETER
Input Reference Frequency
fVCO
PLL VCO Lock Range
fMAX
Output Frequency
MIN
MAX
UNIT
CONDITION
16.67
33.3
MHz
Locked
200
400
MHz
Qa Output used
for feedback
16.67
50
33.3
100
25
75
%
-150
150
5
ps
ns
0.25
1.3
V
VCC-1.7
VCC-0.3
V
50
80
ps
ps
Qa[1:0]d
50
ps/cycle
Qb[2:0]d
25
Qa[1:0]e
400
Qb[2:0]e
200
÷12 feedback
MHz
Qa[1:0]
Qa[1:0]
frefDC
tpd
Reference Input Duty Cycle
Propagation Delay
CLKn to Ext_FB (SPO) c
CLKn to Q (Bypass)
VPP
Differential input voltage (peak-to-peak)
VCMR
Differential input crosspoint voltage
tskew
Output Skew
Within Qa[1:0] or Qb[2:0]
All outputs
∆per/cycle
TYP
PLL_EN = 1
PLL_EN = 0
Rate of change of periods
tpw
Output duty cycle
tjitter
45
55
%
Cycle-to-cyle jitter, Standard deviation (RMS)
40
ps
tlock
Maximum PLL lock time
10
ms
tr/tf
Output Rise/Fall time
700
ps
50
@fref = 25MHz
c. Static phase offset between the selected reference clock and the feedback signal.
d. Specification holds for a clock switch between two signals no greater than 400ps out of phase. Delta period change
per cycle is averaged over the clock switch excursion. (See Applications Information section for more detail)
e. Specification holds for a clock switch between two signals no greater than ±π out of phase. Delta period change per
cycle is averaged over the clock switch excursion.
f. PECL output termination is 50 ohms to VCC – 2.0V.
g. VPP is the minimum differential input voltage swing required to maintain AC characteristic including SPO, device and
part-to-part skew. Applicable to CLK0, CLK1 and Ext_FB.
h. VCMR is the crosspoint of the differential input signal. Normal operation is obtained when the crosspoint is within the
VCMR range and the input swing lies within the VPP specification. Violation of VCMR or VPP impacts the SPO, device
and part-to-part skew. Applicable to CLK0, CLK1 and Ext_FB.
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XRK7933
PRELIMINARY
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
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REV. P1.0.1
APPLICATIONS INFORMATION
The XRK7933 is a dual clock PLL with on–chip Intelligent Dynamic Clock Switch circuitry.
DEFINITIONS
primary clock: The input CLK selected by Sel_Clk.
secondary clock: The input CLK NOT selected by Sel_Clk.
PLL reference signal: The CLK selected as the PLL reference signal by Sel_Clk or the Intelligent Dynamic
Clock Switch. The Intelligent Dynamic Clock Switch can override Sel_Clk.
STATUS FUNCTIONS
Clk_Selected: Clk_Selected (L) indicates CLK0 is selected as the PLL reference signal. Clk_Selected (H)
indicates CLK1 is selected as the PLL reference signal.
Inp0bad, Inp1bad: Inp0bad is latched (H) when CLK0 is stuck (H) or (L) for at least one Ext_FB period, or if one
of the inputs CLK0 or CLK0 is floating. Inp1bad is latched (H) when CLK1 is stuck (H) or (L) for at least one
Ext_FB period, or if one of the inputs CLK1 or CLK1 is floating. Both Inp0bad and Inp1bad are latched (H)
when Ext_FB is stuck (H) or (L) for at least one Qa period, or if one of the inputs Ext_FB or Ext _FB is floating.
Both Inp0bad and Inp1bad are cleared (L) on assertion of Alarm_Reset. The status functions Inp0bad and
Inp1bad are active for Man_Override (H) or (L).
CONTROL FUNCTIONS
Sel_Clk: Sel_Clk (L) selects CLK0 as the primary clock. Sel_Clk (H) selects CLK1 as the primary clock.
Alarm_Reset: Asserted by a negative edge. Generates a one–shot reset pulse that clears INPUT_BAD latches
and Clk_Selected latch.
PLL_En: While (L), the PLL reference signal is substituted for the VCO output.
MR: While (L), internal dividers are held in reset which holds all Q outputs LOW.
MAN OVERRIDE (H)
(IDCS is disabled, PLL functions normally). PLL reference signal (as indicated by Clk_Selected) will always be
the CLK selected by Sel_Clk. If Ext_FB misses at least one pulse, Qa and Qb outputs will drop to a minimum
frequency (~20MHz) for 1-uS, or until Ext_FB shows any activity, whichever is longer. This prevents the Qa
and Qb frequencies from rising due the PLL incorrectly interpreting an intermittent Ext_FB as a VCO running
too slow.
MAN OVERRIDE (L)
Intelligent Dynamic Clock Switch is enabled. The first CLK to fail will latch it’s INP_BAD (H) status flag and
select the other input as the Clk_Selected for the PLL reference clock. Once latched, the Clk_Selected and
INP_BAD remain latched until assertion of Alarm_Reset which clears all latches (INP_BADs are cleared and
Clk_Selected = Sel_Clk).
If both Inp0bad and Inp1bad are (H), either due to both CLK0 and CLK1 having missed at least 1 pulse each or
Ext_FB having missed at least 1 pulse, then Qa and Qb outputs will drop to a minimum frequency (~20MHz)
until such time as Alarm_Reset_b is asserted.
NOTE: If both CLKs are bad when Alarm_Reset is asserted, both INP_BADs will be latched (H) after one Ext_FB period
and Clk_Selected will be latched (L) indicating CLK0 is the PLL reference signal. While neither INP_BAD is latched
(H), the Clk_Selected can be freely changed with Sel_Clk. Whenever a CLK switch occurs, (manually or by the
Intelligent Dynamic Clock Switch), following the next negative edge of the newly selected PLL reference signal, the
next positive edge pair of Ext_FB and the newly selected PLL reference signal will slew to alignment.
To calculate the overall uncertainty between the input CLKs and the outputs from multiple XRK7933’s, the
following procedure should be used. Assuming that the input CLKs to all XRK7933’s are exactly in phase, the
total uncertainty will be the sum of the static phase offset, max I/O jitter, and output to output skew.
During a dynamic switch, the output phase between two devices may be increased for a short period of time. If
the two input CLKs are 400ps out of phase, a dynamic switch of an XRK7933 will result in an instantaneous
phase change of 400ps to the PLL reference signal without a corresponding change in the output phase (due
to the limited response of the PLL). As a result, the I/O phase of a device, undergoing this switch, will initially
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REV. P1.0.1
PRELIMINARY
XRK7933
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
be 400ps and diminish as the PLL slews to its new phase alignment. This transient timing issue should be
considered when analyzing the overall skew budget of a system.
HOT INSERTION AND WITHDRAWAL
In PECL applications, a powered up driver will experience a low impedance path through an XRK7933 input to
its powered down VCC pins. In this case, a 100 ohm series resistance should be used in front of the input pins
to limit the driver current. The resistor will have minimal impact on the rise and fall times of the input signals.
ACQUIRING FREQUENCY LOCK
1. While the XRK7933 is receiving a valid CLK signal, assert Man_Override HIGH.
2. The PLL will phase and frequency lock within the specified lock time.
3. Apply a HIGH to LOW transition to Alarm_Reset to reset Input Bad flags.
4. De–assert Man_Override LOW to enable Intelligent Dynamic Clock Switch mode.
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XRK7933
PRELIMINARY
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
REV. P1.0.1
PACKAGE DIMENSIONS
32 LEAD THIN QUAD FLAT PACK
(7 x 7 x 1.4 mm TQFP)
rev. 2.00
D
D1
24
17
16
25
D
D1
32
9
1
8
B
A2
e
C
A
α
Seating Plane
A1
L
Note: The control dimension is the millimeter column
INCHES
MILLIMETERS
SYMBOL
MIN
MAX
MIN
MAX
A
0.055
0.063
1.40
1.60
A1
0.002
0.006
0.05
0.15
A2
0.053
0.057
1.35
1.45
B
0.012
0.018
0.30
0.45
C
0.004
0.008
0.09
0.20
D
0.346
0.362
8.80
9.20
D1
0.272
0.280
6.90
7.10
e
0.0315 BSC
0.80 BSC
L
0.018
0.030
0.45
0.75
α
0°
7°
0°
7°
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XRK7933
PRELIMINARY
INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
xr
REV. P1.0.1
REVISION HISTORY
REVISION #
DATE
DESCRIPTION
A1.0.0
August 2004
Initial release.
P1.0.0
January 2005
Revised Electrical characteristics, Application Section, changed to Preliminary.
P1.0.1
March 2005
Minor style edits.
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to
improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that
the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user’s specific application. While the information in this publication
has been carefully checked; no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the
failure or malfunction of the product can reasonably be expected to cause failure of the life support system or
to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless
EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has
been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately
protected under the circumstances.
Copyright 2005 EXAR Corporation
Datasheet March 2005.
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
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