74HCT9046A Datasheet, PDF (35/43 Pages) NXP Semiconductors – PLL with bandgap controlled VCO

NXP Semiconductors
74HCT9046A
PLL with band gap controlled VCO
ω_n = ⁵-_t- = ₀----_.-₀-⁵--₀---₁- = 5 × 10³r ⁄ s
Rewriting the equation for natural frequency results in:
τ₁ = ^K-----^p----^×-₍--_ω--^K---_n-^v-₎---₂^×-----^K----ⁿ-
The maximum overshoot occurs at N_max = 30; hence K_n = ¹â„_30:
τ₁ = ⁰---^.--⁴--₅--^×-₀---₀-²--₀-^.--²₂---⁴-_×---^×-₃---₀-¹---⁰---⁶- = 0.0012
When C2 = 470 nF, it follows:
R3‘ = _C--^τ---¹₂- = -₄--₇--⁰-₀--^.--⁰-_×--⁰---₁₁---₀₂---_–--₉- = 2550 Ω
Hence the current source bias resistance
R_bias = 17 × 2550 = 43 kΩ
With ζ = 0.707 (0.5 × τ₂ × ω_n) it follows:
τ₂ = ₀---_.--₅--⁰--_×-^.-⁷---⁰⁵---⁷⁰---₀---₀-- = 0.00028
R4 = _C--^τ---²₂- = -₄---₇₀---_0.-⁰---_×⁰---⁰--₁-²--₀-⁸--_–---₉ = 600 Ω
For extra ripple suppression a capacitor C3 can be connected in parallel with R4, with an
extra τ₃ = R4 × C3.
For stability reasons τ₃ should be < 0.1τ₂, hence C3 < 0.1C2 or C3 = 39 nF.
74HCT9046A_6
Product data sheet
Rev. 06 — 15 September 2009
© NXP B.V. 2009. All rights reserved.
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