74HCT9046A Datasheet, PDF (25/40 Pages) NXP Semiconductors – PLL with bandgap controlled VCO

Philips Semiconductors
PLL with bandgap controlled VCO
Product specification
74HCT9046A
10 ³
P _DEM
(W)
10 ⁴
V _CC=
4.5 V
5.5 V
MBD109
10 ⁵
10
10²
R _s (kΩ)
10 ³
Fig.28 Typical power dissipation.
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
rages shown in Table 2.
Table 2 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 3 Design considerations for VCO section.
SUBJECT
PHASE
COMPARATOR
DESIGN CONSIDERATION
VCO frequency without
extra offset
PC1, PC2
VCO frequency
with extra offset
PC1
PC2
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 Fig.29a.
(Due to R1, C1 time constant a small offset remains when R2 = ∞).
Selection of R1 and C1
Given f_c, determine the values of R1 and C1 using Fig.31.
Given f_max and f_c determine the values of R1 and C1 using Fig.31; use
Fig.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 Fig.29b.
PC1, PC2
PLL conditions with no PC1
signal at the SIG_IN input _PC2
Selection of R1, R2 and C1
Given f_c and f_L determine the value of product R1C1 by using Fig.33.
Calculate f_off from the equation f_off = f_c − 1.6f_L.
Obtain the values of C1 and R2 by using Fig.32.
Calculate the value of R1 from the value of C1 and the product R1C1.
VCO adjusts to f_c with Φ_PCIN = 90° and V_VCOIN = ¹â„₂V_CC.
VCO adjusts to f_offset with Φ_PCIN = −360° and V_VCOIN = minimum.
1999 Jan 11
25