Datasheet

C1 + t1
ǒ
1 *
t2
t3
Ǔ
1 2
C2
3
t ´ t
=
t
R1 +
t3
2
t1(t3 * t2)
t1 +
K
d
K
VCO
w
2
d
(tanf
d
) secf
d
)
t2 +
1
w
d
(tanf
d
) secf
d
)
t3 +
tanf
d
) secf
d
w
d
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: K
VCO
= 2 π × G
VCO
rad/A
f
vco
/f
data
: N = {2, 4, 8, 16, 32}
Phase detector gain: K
d
= iqp × (2 π N)
– 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.
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