C1 + t1 1 *

t

2

t

3

1

2

C2

3

t ´ t

=

t

R1 +

t

32

t

1(t3 * t2)

t1 +

K

dKVCO

w2

d

(

tan f

d

) sec fd)

t2 +

1

w

d(tan fd

) sec fd)

t3 +

tan f

d

) sec fd

wd

DAC5686

www.ti.com ............................................................................................................................................................ SLWS147F – APRIL 2003 – REVISED JUNE 2009

C1, C2, and R1 are then calculated by the following equations:

where

and

Charge pump current:

iqp = 1 mA

VCO gain:

KVCO = 2π × GVCO rad/A

fvco/fdata:

N = {2, 4, 8, 16, 32}

Phase detector gain:

Kd = iqp × (2πN)

–1 A/rad

An Excel™ spreadsheet is available on the TI Web site at http://www-s.ti.com/sc/psheets/scac057/scac057.zip

for automatically calculating the values for C1, C2, and R1.

Completing the preceding example with

PARAMETER

VALUE

UNIT

Gvco

2.00E+02

MHz/V

ω

d

1.00E+00

MHz

N

4

φ

d

80

the component values are

C1 (F)

C2 (F)

R1 (

Ω)

1.44E–08

1.11E–10

1.27E+02

Because the PLL characteristics are not sensitive to these components, the closest 20%-tolerance capacitor and

1%-tolerance resistor values can be used. If the calculation results in a negative value for C2 or an unrealistically

large value for C1, then the phase margin must be reduced slightly.

Copyright © 2003–2009, Texas Instruments Incorporated

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