CD74HC4046A Datasheet, PDF (19/28 Pages) Texas Instruments – High-Speed CMOS Logic Phase-Locked Loop with VCO

CD54HC4046A, CD74HC4046A, CD54HCT4046A, CD74HCT4046A
HC/HCT4046A C_PD
CHIP SECTION
HC
HCT
Comparator 1
48
50
Comparators 2 and 3
39
48
VCO
61
53
UNIT
pF
pF
pF
Application Information
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.
References should be made to Figures 11 through 15 and
Figures 27 through 32 as indicated in the table.
Values of the selected components should be within the
following ranges:
R1
R2
R1 + R2
C1
Between 3kΩ and 300kΩ
Between 3kΩ and 300kΩ
Parallel Value > 2.7kΩ
Greater Than 40pF
SUBJECT
VCO Frequency
Without Extra Offset
PHASE
COMPARATOR
DESIGN CONSIDERATIONS
PC1, PC2 or PC3
VCO Frequency Characteristic
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_o
2f_L
f_MIN
MIN
1/2 V_CC VVCOIN
MAX
FIGURE 44. FREQUENCY CHARACTERISTIC OF VCO OPERATING WITHOUT
OFFSET: f_o = CENTER FREQUENCY: 2f_L = FREQUENCY LOCK RANGE
VCO Frequency with
Extra Offset
PC1
PC2 or PC3
PC1, PC2 or PC3
Selection of R1 and C1
Given f_o, determine the values of R1 and C1 using Figures 11 - 15
≈ ^{Given fMAX calculate fo as fMAX/2 and determine the values of R1 and C1 using Figures 11 -}
15. To obtain 2f_L: 2f_L 1.2 (V_CC - 1.8V)/(R1C1) where valid range of VCO_IN is 1.1V < VCO_IN
< V_CC - 0.9V
VCO Frequency Characteristic
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
f_o
2f_L
f_MIN
MIN
1/2 V_CC VVCOIN MAX
FIGURE 45. FREQUENCY CHARACTERISTIC OF VCO OPERATING WITH OFFSET:
f_o = CENTER FREQUENCY: 2f_L = FREQUENCY LOCK RANGE
PC1, PC2 or PC3
Selection of R1, R2 and C1
≈ Given f_o and f_L, offset frequency, f_MIN, may be calculated from f_MIN f_o - 1.6 f_L.
Obtain the values of C1 and R2 by using Figures 27 - 30.
Calculate the values of R1 from Figures 31 - 32.
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