CD54HC4046A, CD74HC4046A, CD54HCT4046A, CD74HCT4046A
HC/HCT4046A C
PD
References should be made to Figures 11 through 15 and
Figures 27 through 32 as indicated in the table.
CHIP SECTION
HC
48
39
61
HCT
50
UNIT
pF
Values of the selected components should be within the
following ranges:
Comparator 1
Comparators 2 and 3
VCO
48
pF
53
pF
R1
Between 3kΩ and 300kΩ
Between 3kΩ and 300kΩ
Parallel Value > 2.7kΩ
Greater Than 40pF
R2
Application Information
R1 + R2
C1
This information is a guide for the approximation of values of
external components to be used with the ’HC4046A and
’HCT4046A in a phase-lock-loop system.
PHASE
SUBJECT
COMPARATOR
DESIGN CONSIDERATIONS
VCO Frequency
PC1, PC2 or PC3 VCO Frequency Characteristic
Without Extra Offset
With R2 = ∞ and R1 within the range 3kΩ < R1 < 300kΩ, the characteristics of the VCO
operation will be as shown in Figures 11 - 15. (Due to R1, C1 time constant a small offset
remains when R2 = ∞.)
f
MAX
f
VCO
f
2f
o
L
f
MIN
V
MIN
1/2 V
MAX
VCOIN
CC
FIGURE 44. FREQUENCY CHARACTERISTIC OF VCO OPERATING WITHOUT
OFFSET: f = CENTER FREQUENCY: 2f = FREQUENCY LOCK RANGE
o
L
PC1
Selection of R1 and C1
Given f , determine the values of R1 and C1 using Figures 11 - 15
o
PC2 or PC3
Given f
calculate f as f
/2 and determine the values of R1 and C1 using Figures 11 -
- 1.8V)/(R1C1) where valid range of VCO is 1.1V < VCO
IN
MAX
o
MAX
15. To obtain 2f : 2f ≈ 1.2 (V
L
L
CC
IN
< V
- 0.9V
CC
VCO Frequency with PC1, PC2 or PC3 VCO Frequency Characteristic
Extra Offset
With R1 and R2 within the ranges 3kΩ < R1 < 300kΩ, 3kΩ, < R2 < 300kΩ, the characteristics
of the VCO operation will be as shown in Figures 27 - 32.
f
MAX
f
VCO
2f
f
L
o
f
MIN
V
MIN
1/2 V
MAX
VCOIN
CC
FIGURE 45. FREQUENCY CHARACTERISTIC OF VCO OPERATING WITH OFFSET:
= CENTER FREQUENCY: 2f = FREQUENCY LOCK RANGE
f
o
L
PC1, PC2 or PC3 Selection of R1, R2 and C1
Given f and f , offset frequency, f
, may be calculated from fMIN ≈ f - 1.6 f .
o
L
MIN
o
L
Obtain the values of C1 and R2 by using Figures 27 - 30.
Calculate the values of R1 from Figures 31 - 32.
19
TI [ TEXAS INSTRUMENTS ]
