MAX3672 Просмотр технического описания (PDF) - Maxim Integrated
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MAX3672 Datasheet PDF : 12 Pages
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Low-Jitter 155MHz/622MHz Clock Generator
Bond Pad Coordinates
LOL Setup
The LOL output indicates if the PLL has locked onto the
PAD
PAD COORDINATES (µm)
X
Y
reference clock using an XOR gate and comparator. The
comparator threshold can be adjusted with THADJ, and
1
50.8
2
50.8
1557.3
1408.8
the XOR gate output can be filtered with a capacitor
between CTH and ground (Figure 3). When the voltage
at pin CTH exceeds the voltage at pin THADJ, then the
3
50.8
1179.3
LOL output goes low and indicates that the PLL is not
4
50.8
1028.1
locked. Note that excessive jitter on the reference clock
5
50.8
6
50.8
7
50.8
8
50.8
874.2
720.4
566.5
412.6
input at frequencies above the loop bandwidth may
degrade LOL functionality.
The user can set the amount of frequency or phase dif-
ference between VCO and reference clock at which
LOL indicates an out-of-lock condition. The frequency
9
50.8
258.7
difference is called the beat frequency. The CTH pin
10
266.8
11
420.7
50.8
can be connected to an external capacitor, which sets
50.8
the lowpass filter frequency to approximately
12
574.6
13
728.5
14
882.4
15
1036.2
16
1190.1
17
1344
18
1549.2
19
1792.2
20
1792.2
21
1792.2
22
1792.2
23
1792.2
24
1792.2
25
1792.2
26
1792.2
27
1792.2
50.8
50.8
50.8
50.8
50.8
50.8
50.8
256
409.9
563.8
717.7
871.6
1025.4
1179.3
1333.2
1530.3
fL
=
1
2πC TH 60kΩ
This lowpass filter frequency should be set about 10
times lower then the beat frequency to ensure that the
filtered signal at CTH does not drop below the THADJ
threshold voltage. Internal comparisons occur at the
pre-divider output frequency (see Table 1 for VCO and
reference clock setup). For example, assume the pre-
divider output frequency is 19.44MHz. For a 1ppm sen-
sitivity, the minimum beat frequency is 19Hz, and the
filter should be set to 1.9Hz. Set CTH to 1.36uF.
The voltage at THADJ will determine the level at which
the LOL output flags. THADJ is set to a default value of
0.6V which corresponds to a 45° phase difference. This
value can be overridden by applying the desired
threshold voltage to the THADJ input. The range of
THADJ is 0V (0°) to 2.4V (180°).
28
1792.2
1692.3
29
1565.4
1692.3
30
1411.5
1692.3
31
1257.6
1692.3
32
1103.7
1692.3
33
893.2
1692.3
34
685.3
1692.3
35
531.4
1692.3
36
377.5
1692.3
37
223.6
1692.3
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