ICS841654I Datasheet, PDF (9/17 Pages) Integrated Device Technology – FEMTOCLOCKS™ CRYSTAL-TO-HCSL CLOCK GENERATOR

ICS841654I
FEMTOCLOCKS™ CRYSTAL-TO-HCSL CLOCK GENERATOR
PARAMETER MEASUREMENT INFORMATION, CONTINUED
VMAX = 1.15V
nQ
VCROSS_MAX = 550mV
VCROSS_MIN = 250mV
Q
VMIN = -0.30V
SE MEASUREMENT POINTS FOR ABSOLUTE CROSS POINT/SWING
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. To achieve optimum jitter per-
formance, power supply isolation is required. The ICS841654I
provides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_DD, V_DDA, V_DDOA and
V_DDOB should be individually connected to the power supply
plane through vias, and 0.01µF bypass capacitors should be
used for each pin. Figure 1 illustrates this for a generic V pin
DD
and also shows that V_DDA requires that an additional10Ω
resistor along with a 10µF bypass capacitor be connected to
the V_DDA pin.
3.3V
V_DD
.01μF 10Ω
V_DDA
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
INPUTS:
CRYSTAL INPUTS
For applications not requiring the use of the crystal oscillator input,
both XTAL_IN and XTAL_OUT can be left floating. Though not
required, but for additional protection, a 1kΩ resistor can be tied
from XTAL_IN to ground.
REF_IN INPUT
For applications not requiring the use of the reference clock,
it can be left floating. Though not required, but for additional
protection, a 1kΩ resistor can be tied from the REF_IN to ground.
LVCMOS CONTROL PINS
All control pins have internal pull-ups or pull-downs; additional
resistance is not required but can be added for additional
protection. A 1kΩ resistor can be used.
OUTPUTS:
HCSL OUTPUTS
All unused HCSL outputs can be left floating. We recommend
that there is no trace attached. Both sides of the differential output
pair should either be left floating or terminated.
LVCMOS OUTPUT
The unused LVCMOS output can be left floating. We recommend
that there is no trace attached.
IDT^™ / ICS^™ HCSL CLOCK GENERATOR
9
ICS841654AGI REV. A APRIL 17, 2008