MK1574 Integrated Circuit System, MK1574 Datasheet - Page 4

• Manufacturer Part Number: MK1574
• Description: Frame Rate Communications PLL
• Manufacturer: Integrated Circuit System

MDS1574-01D
Integrated Circuit Systems, Inc. • 525 Race Street • San Jose • CA • 95126 • [phone] www.icst.com
Loop Bandwidth and Loop Filter Component Selection
The series-connected capacitor and resistor between CAP1 and CAP2 (pins 4 and 6) determine the dynamic
characteristics of the phase-locked loop. The capacitor must have very low leakage, therefore a high quality
ceramic capacitor is recommended. DO NOT use any type of polarized or electrolytic capacitor. The series
connected capacitor and resistor between CAP1 and CAP2 (pins 4 and 6) determine the dynamic
characteristics of the phase-locked loop. The capacitor must have very low leakage, therefore a high quality
ceramic capacitor is recommended. DO NOT use any type of polarized or electrolytic capacitor. Ceramic
capacitors should have C0G or NP0 dielectric. Avoid high-K dielectrics like Z5U and X7R; these and other
ceramics which have piezoelectric properties allow mechanical vibration in the system to increase the output
jitter because the mechanical energy is converted directly to voltage noise on the VCO input.
The values of the RC network determine the bandwidth of the PLL. The values of the loop filter components
are calculated using the constants K1 and K2 from the table on page 5. The loop bandwidth is set by the
capacitor C and the constant K1 using the formula
The loop damping is set by the resistor R, the capacitor C, and the constant K2 using the formula
For example, to design the loop filter when generating 8.192 MHz from 8 kHz:
1. From the table on page 2, the address is E. The table on page 5 shows constants K1=0.0516 and K2=6.2.
2. A good value for the loop bandwidth is 1/20 the input frequency; where 8 kHz/20 = 400 Hz. Using
3. A good value for the damping factor is 0.707. From Equation 2,
Equation 1,
Therefore,
I C R O
R =
BW (Hz) =
C =
400 =
R =
C
(
0.0516
0.707 • 6.2
0.0516
LOC K
400
• K2
16E-9
C
C
K1
C
)
2
= 16.6 nF (16 nF nearest standard value)
= 34.7 k
4
Frame Rate Communications PLL
Equation 1
Equation 2
(36 k nearest standard value)
;
(zeta) is the damping factor
MK1574
Revision 011601