ICS10001B21 View Datasheet(PDF) - Integrated Circuit Systems
Part Name
Description
MFG CO.
'ICS10001B21' PDF : 21 Pages View PDF
Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS810001-21
FEMTOCLOCKS™ DUAL VCXO VIDEO PLL
NOTES ON SETTING CHARGE PUMP CURRENT
The recommended range for the charge pump current is 50μA
to 300μA. Below 50μA, loop filter charge leakage, due to PCB or
capacitor leakage, can become a problem. This loop filter leakage
can cause locking problems, output clock cycle slips, or low
frequency phase noise.
As can be seen in the loop bandwidth and damping factor
equations or by using the filter response software available from
ICS, increasing charge pump current (ICP) increases both
bandwidth and damping factor.
CHARGE PUMP CURRENT, EXAMPLE SETTINGS
RSET
17.6k
8.8k
4.4k
2.2k
Charge Pump Current (ICP)
62.5µA
125µA
250µA
500µA
1E-3
100E-6
10E-6
1k
10k
RSET, Ω
100k
FIGURE 2. CHARGE PUMP CURRENT VS. VALUE OF RSET (EXTERNAL RESISTOR) GRAPH
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS810001-21 provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. VDD, VDDA, VDDx, and
V should be individually connected to the power supply
DDO
plane through vias, and bypass capacitors should be
used for each pin. To achieve optimum jitter performance,
power supply isolation is required. Figure 3 illustrates how
a 10Ω resistor along with a 10μF and a .01μF bypass
capacitor should be connected to each VDDA pin.
VDD
VDDA
3.3V
.01μF 10Ω
.01μF
10μF
FIGURE 3. POWER SUPPLY FILTERING
810001BK-21
www.icst.com/products/hiperclocks.html
18
REV. A AUGUST 12, 2005
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