74HCT9046A Datasheet, PDF (27/43 Pages) NXP Semiconductors – PLL with bandgap controlled VCO

NXP Semiconductors
74HCT9046A
PLL with band gap controlled VCO
13. Application information
This information is a guide for the approximation of values of external components to be
used with the 74HCT9046A in a phase-locked-loop system.
Values of the selected components should be within the ranges shown in Table 7.
Table 7. Survey of components
Component
R1
R2
R1 + R2
C1
Value
between 3 kΩ and 300 kΩ
between 3 kΩ and 300 kΩ
parallel value > 2.7 kΩ
> 40 pF
Table 8. Design considerations for VCO section
Subject
Phase comparator
Design consideration
VCO frequency
without extra
offset
PC1, PC2
VCO frequency characteristic. With R2 = ∞ and R1 within the range
3 kΩ < R1 < 300 kΩ, the characteristics of the VCO operation will be as
shown in Figure 29a. (Due to R1, C1 time constant a small offset remains
when R2 = ∞ Ω).
PC1
Selection of R1 and C1. Given f₀, determine the values of R1 and C1 using
Figure 31.
VCO frequency
with extra offset
PC2
PC1, PC2
Given f_max and f₀ determine the values of R1 and C1 using Figure 31; use
Figure 33 to obtain 2f_L and then use this to calculate f_min.
VCO frequency characteristic. With R1 and R2 within the ranges
3 kΩ < R1 < 300 kΩ < R2 < 300 kΩ, the characteristics of the VCO
operation is as shown in Figure 29b.
PC1, PC2
Selection of R1, R2 and C1. Given f₀ and f_L determine the value of product
R1C1 by using Figure 33. Calculate f_off from the equation f_off = f₀ − 1.6f_L.
Obtain the values of C1 and R2 by using Figure 32. Calculate the value of
R1 from the value of C1 and the product R1C1.
PLL conditions with PC1
no signal at pin
PC2
SIG_IN
VCO adjusts to f₀ with Φ_{PC_IN} = 90° and V_{VCO_IN} = 0.5V_CC
VCO adjusts to f_offset with Φ_{PC_IN} = −360° and V_{VCO_IN} = minimum
74HCT9046A_6
Product data sheet
Rev. 06 — 15 September 2009
© NXP B.V. 2009. All rights reserved.
27 of 43