CD54HC4046AF datasheet(19/37 Pages) TI2

19 / 37 page

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:

HC/HCT4046A CPD

CHIP SECTION

HCT

UNIT

Comparator 1

Comparators 2 and 3

VCO

Between 3k

Ω and 300kΩ

Between 3k

Ω and 300kΩ

R1 + R2

Parallel Value > 2.7k

Ω

Greater Than 40pF

SUBJECT

PHASE

COMPARATOR

DESIGN CONSIDERATIONS

VCO Frequency

Without Extra Offset

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 =

∞.)

PC1

Selection of R1 and C1

Given fo, determine the values of R1 and C1 using Figures 11 - 15

PC2 or PC3

Given fMAX calculate fo as fMAX/2 and determine the values of R1 and C1 using Figures 11 -

15. To obtain 2fL:2fL

≈ 1.2 (V

CC - 1.8V)/(R1C1) where valid range of VCOIN is 1.1V < VCOIN

< VCC - 0.9V

VCO Frequency with

Extra Offset

PC1, PC2 or PC3

VCO Frequency Characteristic

With R1 and R2 within the ranges 3k

Ω < R1 < 300kΩ,3kΩ, < R2 < 300kΩ, the characteristics

of the VCO operation will be as shown in Figures 27 - 32.

PC1, PC2 or PC3

Selection of R1, R2 and C1

Given fo and fL, offset frequency, fMIN, may be calculated from fMIN

≈ f

o - 1.6 fL.

Obtain the values of C1 and R2 by using Figures 27 - 30.

Calculate the values of R1 from Figures 31 - 32.

FIGURE 44. FREQUENCY CHARACTERISTIC OF VCO OPERATING WITHOUT

OFFSET: fo = CENTER FREQUENCY: 2fL = FREQUENCY LOCK RANGE

fMAX

fVCO

fMIN

MIN

1/2 VCC VVCOIN

MAX

2fL

FIGURE 45. FREQUENCY CHARACTERISTIC OF VCO OPERATING WITH OFFSET:

fo = CENTER FREQUENCY: 2fL = FREQUENCY LOCK RANGE

fMAX

fVCO

fMIN

MIN

1/2 VCC

VVCOIN

MAX

2fL

CD54HC4046A, CD74HC4046A, CD54HCT4046A, CD74HCT4046A

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