74hct4046a NXP Semiconductors, 74hct4046a Datasheet - Page 25

• Manufacturer Part Number: 74hct4046a
• Description: Phase-locked-loop With Vco
• Manufacturer: NXP Semiconductors

Philips Semiconductors
APPLICATION INFORMATION
This information is a guide for the approximation of values of external components to be used with the 74HC/HCT4046A
in a phase-lock-loop system.
References should be made to Figs 29, 30 and 31 as indicated in the table.
Values of the selected components should be within the following ranges:
R1
R2
R1 + R2 parallel value
C1
1997 Nov 25
SUBJECT
VCO frequency
without extra
offset
Phase-locked-loop with VCO
between 3 k and 300 k ;
between 3 k and 300 k ;
greater than 40 pF.
PC1
PC2 or PC3
PHASE
COMPARATOR
PC1, PC2 or PC3
2.7 k ;
DESIGN CONSIDERATIONS
VCO frequency characteristic
With R2 =
characteristics of the VCO operation will be as shown in Fig.25.
(Due to R1, C1 time constant a small offset remains when R2 = .).
Fig.25 Frequency characteristic of VCO operating without offset:
f
Selection of R1 and C1
Given f
Given f
Fig.31 to obtain 2f
0
= centre frequency; 2f
max
o
, determine the values of R1 and C1 using Fig.29.
and f
25
and R1 within the range 3 k
o
, determine the values of R1 and C1 using Fig.29, use
L
and then use this to calculate f
L
= frequency lock range.
74HC/HCT4046A
R1
300 k , the
min
Product specification
.