DATASHEET
16 OUTPUT LOW SKEW CLOCK GENERATOR
Description
The MK74CG117A is a monolithic CMOS high-speed,
low-skew clock driver that includes an on-chip PLL. Ideal for
communications and other systems that require a large
number of high-speed clocks, the unique combination of
PLL and 16 low-skew outputs can eliminate oscillators and
low-skew buffers from systems.
The device has a number of built-in multipliers, making it
possible to run from one inexpensive, low-frequency
crystal, and produce high-frequency clock outputs. Another
selection allows the chip to run as a divider, dividing the
input clock by two (or 4 using the mode select).
The device also has a buffered reference output, allowing
multiple devices to be easily driven from one clock source.
MK74CG117A
Features
•
48-pin SSOP (300 mil) package
•
On-chip PLL generates output clocks up to 90 MHz from
a simple crystal or clock input
•
16 low-skew outputs
•
Output skew less than 350 ps on rising edges
•
Ability to configure as
– 16 clocks at full-frequency
– 12 at full and 4 at half-frequency
– 8 at full and 8 at half-frequency
•
Tri-state mode for Output Enable function
•
3.3 V ±5% supply voltage
Block Diagram
VDD
9
S2:0
M1:0
3
2
Clock
Synthesis
and Mode
Select
Circuitry
Clock 1
Clock 2
Crystal or
clock input
X1/ICLK
Crystal
Ocsillator
X2
Clock 16
REF
The crystal requires external capacitors for
accurate tuning of the clock
10
GND
IDT™ / ICS™
16 OUTPUT LOW SKEW CLOCK GENERATOR
1
MK74CG117A REV F 082704
MK74CG117A
16 OUTPUT LOW SKEW CLOCK GENERATOR
CLOCK SYNTHESIZER
Pin Assignment
VDD
X1/ICLK
X2
NC
NC
GND
GND
S2
REF
S1
GND
GND
CLK1
CLK2
VDD
VDD
CLK3
CLK4
GND
GND
NC
CLK5
CLK6
VDD
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
S0
CLK16
VDD
VDD
NC
CLK15
CLK14
GND
GND
M1
CLK13
CLK12
VDD
VDD
M0
CLK11
CLK10
CLK9
VDD
NC
GND
GND
CLK8
CLK7
48-pin (300 mil) SSOP
IDT™ / ICS™
16 OUTPUT LOW SKEW CLOCK GENERATOR
2
MK74CG117A REV F 082704
MK74CG117A
16 OUTPUT LOW SKEW CLOCK GENERATOR
CLOCK SYNTHESIZER
Pin Descriptions
Pin Number
Pin Name
Pin Type
Pin Description
1, 15, 16, 24, 30, 35, 36, 45, 46
2
3
4, 5, 21, 29, 44
6, 7, 11, 12, 19, 20, 27, 28, 40, 41
8, 10, 48
9
13, 14, 17, 18
22, 23, 25, 26, 31, 32, 33, 37
34, 39
38, 42, 43, 47
VDD
X1/ICLK
X2
NC
GND
S2, S1, S0
REF
CLK1 - 4
CLK5 - 12
M0, M1
CLK13 - 16
Power
XI
XO
—
Power
Input
Output
Output
Output
Input
Output
Connect to VDD.
Connect to a crystal input or clock.
Connect to a crystal or leave unconnected for clock
input.
No connect. Nothing is connected to these pins.
Connect to ground.
Multiplier select pins. See table 2.
Crystal oscillator buffered reference clock output.
Clock 1-4. Can be either full or half-speed per Table 1.
Clock outputs 5-12. At full (1x) speed unless tri-stated
per Table 1.
Mode Select pins. Selects tri-state or speed of outputs
per Table 1.
Clock 13-16. Can be either full or half-speed per Table
1.
External Components
The MK74CG117A requires a minimum number of external
components for proper operation.
Decoupling Capacitor
A decoupling capacitor of 0.1µF must be connected
between each VDD and GND. Connect the capacitor as
close to these pins as possible. For optimum device
performance, mount the decoupling capacitor on the
component side of the PCB. Avoid the use of vias in the
decoupling circuit.
3) An optimum layout is one with all components on the
same side of the board, thus minimizing vias through other
signal layers. Other signal traces should be routed away
from the MK74CG117A device. This includes signal traces
located underneath the device, or on layers adjacent to the
ground plane layer used by the device.
Crystal Information
The crystal used should be a fundamental mode (do not use
third overtone), parallel resonant crystal. The oscillator has
internal caps that provide the proper load for a crystal with
C
L
= 18 pF. The value of these capacitors is given by the
following equation:
Crystal caps (pF) = (C
L
- 18) x 2
PCB Layout Recommendations
For optimum device performance and lowest output phase
noise, observe the following guidelines:
1) Mount the 0.01µF decoupling capacitor on the
component side of the board as close to the VDD pin as
possible. No vias should be used between the decoupling
capacitor and VDD pin. The PCB trace to the VDD pin and
the PCB trace to the ground via should be kept as short as
possible.
2) To minimize EMI, place the 33Ω series-termination
resistor (if needed) close to the clock output.
IDT™ / ICS™
16 OUTPUT LOW SKEW CLOCK GENERATOR
3
MK74CG117A REV F 082704
MK74CG117A
16 OUTPUT LOW SKEW CLOCK GENERATOR
CLOCK SYNTHESIZER
Power Dissipation, Termination, and Operating
Frequency
As with all clock drivers, the power dissipated by the
MK74CG117A is affected by the external loading on the
output pins. This consists of the capacitance of the load that
is being driven, as well as the PC board trace itself. Since
this capacitance must be charged and discharged with each
cycle of the output clock, as the frequency goes up, so does
the power required. Operating below the specified
maximum output clock frequency shown in Table 2 will keep
the MK74CG117A power dissipation within acceptable
limits.
External series termination resistors must be used in series
with each output. These resistors serve two purposes: The
first is to match the source impedance to the line (PC board
trace) that is being driven. This will minimize reflections that
cause non-linear transitions on the output clock waveform.
The output impedance of the MK74CG117A is
approximately 20Ω; assuming a 50Ω line, then a 33Ω
resistor should be used at each output as shown in Figure 1.
Table 2. Multiplier Selections (Input and CLK
Frequencies in MHz)
S2
S1 S0
0
0
0
Input
33–50
Multiplier
0.5
CLK Out
16.5–25
Comments
Divider
only; no
PLL
PLL
PLL
PLL
PLL
PLL
PLL
PLL
0
0
0
1
1
1
1
0
1
1
0
0
1
1
1
0
1
0
1
0
1
20–50
16–40
10–45
8–36
8–27
8–22.5
8–18
1
1.25
2
2.5
3.333
4
5
20–50
20–50
20–90
20–90
26.7–90
32–90
40–90
Figure 1. External Termination
33 ohm
Table 1. Tri-state and Mode Select
M1
M0
Mode
at
CLK(1x)
Z
at
CLK/2(0.5x)
Z
Max
Output
Freq.
MK74CG117
Output
To load
0
0
All outputs,
including
REF,
tri-stated
12 @ 1x,
4 @ 0.5x
8 @ 1x,
8 @ 0.5x
16 outputs
@ 1x
As speeds rise, the limiting factor in device operation
becomes the power generated by having a large number of
drivers in one package. Using the external termination
resistors reduces the power dissipated within the device,
allowing output frequencies up to 100 MHz.
83.3 MHz
0.8
83.3 MHz
1.25
90 MHz
0
1
1
1
0
1
CLK1–12
CLK5–12
CLK1–16
CLK13–16
CLK1–4,
13–16
None
Note that the maximum operating frequency of the
MK74CG117A is determined by the Mode selected from
Table 1 and the Multiplier selected from Table 2. For output
frequencies above 83.3 MHz, all 16 outputs must be at the
same frequency (M1=M0=1).
When operating with a combination of 1X and 0.5X outputs,
the output frequency cannot exceed 83.3 MHz.
IDT™ / ICS™
16 OUTPUT LOW SKEW CLOCK GENERATOR
4
MK74CG117A REV F 082704
MK74CG117A
16 OUTPUT LOW SKEW CLOCK GENERATOR
CLOCK SYNTHESIZER
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the MK74CG117A. These ratings, which
are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of the device, at
these or any other conditions, above those indicated in the operational sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods can affect product reliability. Electrical
parameters are guaranteed only over the recommended operating temperature range.
Item
Supply Voltage, VDD (referenced to GND)
All Inputs and Outputs (referenced to GND)
Ambient Operating Temperature
Storage Temperature
Junction Temperature
Soldering Temperature
7V
Rating
0.5 V to VDD+0.5 V
0 to +70°C
-65 to +150°C
125°C
260°C
Recommended Operation Conditions
Parameter
Ambient Operating Temperature
Power Supply Voltage (measured in respect to GND)
Min.
0
+3.14
Typ.
Max.
+70
3.47
Units
°C
V
DC Electrical Characteristics
Unless stated otherwise,
VDD = 3.3 V ±5%,
Ambient Temperature 0 to +70°C
Parameter
Operating Voltage
Supply Current (at 50
MHz)
Input High Voltage,
ICLK
Input Low Voltage,
ICLK
Output High Voltage
Output High Voltage
Output Low Voltage,
3.3 V
Short Circuit Current
Input Capacitance
Symbol
VDD
IDD
V
IH
V
IL
V
OH
V
OH
V
OL
No load
pin 2
pin 2
Conditions
Min.
3.14
Typ.
3.3
63
Max.
3.47
Units
V
mA
V
VDD-1
VDD/2
VDD/2
1
V
V
V
I
OH
= -8 mA
I
OH
= -12 mA
I
OL
= 12 mA
Each output
VDD-0.4
2.0
0.4
±35
7
V
mA
pF
C
IN
S0, S1, FRSEL pins
IDT™ / ICS™
16 OUTPUT LOW SKEW CLOCK GENERATOR
5
MK74CG117A REV F 082704
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