74hc7046a NXP Semiconductors, 74hc7046a Datasheet - Page 27

• Manufacturer Part Number: 74hc7046a
• Description: Phase-locked-loop With Lock Detector
• 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/HCT7046
in a phase-lock-loop system.
References should be made to Figs 27, 28 and 29 as indicated in the table.
Values of the selected components should be within the following ranges:
December 1990
R1
R2
R1
C1
SUBJECT
VCO frequency
without extra
offset
Phase-locked-loop with lock detector
R2
between 3 k and 300 k
between 3 k and 300 k
parallel value 2.7 k ;
greater than 40 pF.
PHASE
COMPARATOR
PC1, PC2
PC1
PC2
DESIGN CONSIDERATIONS
VCO frequency characteristic
With R2 =
of the VCO operation will be as shown in Fig. 23.
(Due to R1, C1 time constant a small offset remains when R2 = .)
Selection of R1 and C1
Given f
Given f
use Fig.29 to obtain 2f
Fig. 23 Frequency characteristic of VCO operating without offset:
o
max
, determine the values of R1 and C1 using Fig.27.
and f
and R1 within the range 3 k
f
o
= centre frequency; 2f
o
27
, determine the values of R1 and C1 using Fig.27,
L
and then use this to calculate f
L
= frequency lock range.
R1 300 k , the characteristics
74HC/HCT7046A
min.
Product specification