Document
2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
DATASHEET
ICS557-06
Description
The ICS557-06 is a two to four differential clock mux designed for use in PCI-Express applications. The device selects one of the two differential HCSL input pairs and fans out to four pairs of differential HCSL or LVDS outputs.
Features
• Packaged in 20-pin TSSOP • Pb (lead) free packaging • Operating voltage of 3.3 V • Low power consumption • Input differential clock of up to 200 MHz • Jitter 60 ps (cycle-to-cycle) • Output-to-output skew of 50 ps • Available in industrial temperature range (-40 to +85°C) • For PCIe Gen2/3 applications, see the 5V41067A
Block Diagram
IN1 IN1 IN2 IN2
VDD 2
MUX 2 to 1
2
SEL GND
PD
OE
Rr (IREF)
CLKA CLKA CLKB CLKB CLKC CLKC CLKD CLKD
IDT® 2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
1
ICS557-06 REV M 070512
ICS557-06 2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
PCIE FAN OUT BUFFER
Pin Assignment
SEL
1
VDDIN
2
IN1
3
IN1
4
PD
5
IN2
6
IN2
7
OE
8
GND
9
IREF
10
20
CLKA
19
CLKA
18
CLKB
17
CLKB
16
GND
15
VDD
14
CLKC
13
CLKC
12
CLKD
11
CLKD
20-pin (173 mil) TSSOP
Select Table
SEL
0 1
Input Pair selected
IN2/ IN2 IN1/ IN1
Pin Descriptions
Pin
Pin
Pin
Name
Type
Pin Description
1
SEL
Input SEL=1 selects IN1/IN1. SEL =0 selects IN2/ IN2. Internal pull-up resistor.
2
VDDIN
Power Connect to +3.3 V. Supply voltage for Input clocks.
3
IN1
Input HCSL true input signal 1.
4
IN1
Input HCSL complimentary input signal 1.
5
PD
Input Powers down the chip and tri-states outputs when low. Internal pull-up
6
IN2
Input HCSL true input signal 2.
7
IN2
Input HCSL complimentary input signal 2.
8
OE
Input Provides fast output on, tri-states output (High = enable outputs; Low =
disable). Internal pull-up resistor outputs.
9
GND
Power Connect to ground.
10
Rr(IREF) Output Precision resistor attached to this pin is connected to the internal current
11
CLKD
Output Differential Complimentary output clock D.
12
CLKD
Output Differential True output clock D.
13
CLKC
Output Differential Complimentary output clock C.
14
CLKC
Output Differential True output clock C.
15
VDDOUT Power Connect to +3.3 V. Supply Voltage for Output Clocks.
16
GND
Power Connect to ground.
17
CLKB
Output Differential Complimentary output clock B.
18
CLKB
Output Differential True output clock B.
19
CLKA
Output Differential Complimentary output clock A.
20
CLKA
Output Differential True output clock A.
IDT® 2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
2
ICS557-06 REV M 070512
ICS557-06 2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
PCIE FAN OUT BUFFER
Application Information
Decoupling Capacitors
As with any high-performance mixed-signal IC, the ICS557-06 must be isolated from system power supply noise to perform optimally.
Decoupling capacitors of 0.01µF must be connected between each VDD and the PCB ground plane.
PCB Layout Recommendations
For optimum device performance and lowest output phase noise, the following guidelines should be observed.
Each 0.01µF decoupling capacitor should be mounted on the component side of the board as close to the VDD pin as possible. No vias should be used between decoupling capacitor and VDD pin. The PCB trace to VDD pin should be kept as short as possible, as should the PCB trace to the ground via. Distance of the ferrite bead and bulk decoupling from the device is less critical.
2) An optimum layout is one with all components on the same side of the board, minimizing vias through other signal layers (the ferrite bead and bulk decoupling capacitor can be mounted on the back). Other signal traces should be routed away from the ICS557-06.
This includes signal traces just underneath the device, or on layers adjacent to the ground plane layer used by the device.
External Components
A minimum number of external components are required for proper operation. Decoupling capacitors of 0.01 μF should be connected between VDD and GND pairs (2,9 and 15,16) as close to the device as possible.
Current Reference Source Rr (Iref)
If board target trace impedance (Z) is 50Ω, then Rr = 475Ω (1%), providing IREF of 2.32 mA, output current (IOH) is equal to 6*IREF.
Load Resistors RL
Since the clock outputs are open source outputs, 50 ohm external resistors to ground are to be connected at each clock output.
Output Termination
The PCI-Express differential clock outputs of the ICS557-06 are open source drivers and require an external series resistor and a resistor to ground. These resistor values and their allowable locations are shown in detail in the PCI-Express Layout Guidelines section.
The ICS557-06 can also be configured for LVDS compatible voltage levels. See the LVDS Compatible Layout Guidelines section.
IDT® 2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
3
ICS557-06 REV M 070512
ICS557-06 2 TO 4 DIFFERENTIAL PCIE GEN1 CLOCK MUX
Output Structures
IREF =2.3 mA
6*IREF
See Output Termination
RR 475Ω Sections - Pages 3.