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參數(shù)資料
| 型號： | XRK4991ACJ-5 |
| 廠商： | EXAR CORP |
| 元件分類： | 時鐘及定時 |
| 英文描述： | 3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER |
| 中文描述： | 4991 SERIES, PLL BASED CLOCK DRIVER, 8 TRUE OUTPUT(S), 0 INVERTED OUTPUT(S), PQCC32 |
| 封裝： | PLASTIC, LCC-32 |
| 文件頁數(shù)： | 4/13頁 |
| 文件大?。?/td> | 255K |
| 代理商： | XRK4991ACJ-5 |
XRK4991A
3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER
PRELIMINARY
xr
REV. P1.0.2
4
EXTERNAL FEEDBACK
By providing external feedback, the XRK4991A gives users flexibility with regard to skew adjustment. The
FB_IN signal is compared with the input CLKIN signal at the phase detector in order to drive the VCO. Phase
differences cause the VCO to adjust upwards or downwards accordingly. An internal loop filter moderates the
response of the VCO to the phase detector. The loop filter transfer function has been chosen to provide
minimal jitter (or frequency variation) while still providing accurate responses to input frequency changes.
T
ABLE
1: PLL P
ROGRAMMABLE
S
KEW
R
ANGE
AND
R
ESOLUTION
T
ABLE
N
OTES
:
1.
The device may be operated outside recommended frequency ranges without damage, but functional operation is
not guaranteed. Selecting the appropriate FSEL value based on input frequency range allows the PLL to operate
in its ‘sweet spot’ where jitter is lowest.
The level to be set on FSEL is determined by the nominal operating frequency of the VCO and Time Unit
Generator. The VCO frequency always appears at QA[1:0], QB[1:0] and the higher outputs when they are
operated in their undivided modes. The frequency appearing at the CLKIN and FB_IN inputs will be the same as
the VCO when the output connected to FB_IN is undivided. The frequency of the CLKIN and FB_IN inputs will be
1/2 or 1/4 the VCO frequency when the part is configured for a frequency multiplication by using a divided output
as the FB_IN input.
Skew adjustment range assumes that a zero skew output is used for feedback. If a skewed Q output is used for
feedback, then adjustment range will be greater. For example if a 4t
U
skewed output is used for feedback, all other
outputs will be skewed –4t
U
in addition to whatever skew value is programmed for those outputs. ‘Max adjustment’
range applies to output pairs 3 and 4 where ± 6t
U
skew adjustment is possible and at the lowest FNOM value.
2.
3.
FSEL = LOW
FSEL = MID
FSEL = HIGH
C
OMMENTS
Timing Unit Calculation (t
U
)
1/(44 x F
NOM
)
1/(26 x F
NOM
)
1/(16 x F
NOM
)
VCO Frequency Range (F
NOM
)
(1,2)
15 to 35MHz
25 to 60MHz
40 to 100MHz
Skew Adjustment Range
(3)
Max Adjustment:
+9.09ns
+9.23ns
+9.38ns
ns
+49°
+83°
+135°
Phase Degrees
+14%
+23%
+37%
% of Cycle Time
Example 1, F
NOM
= 15MHz
t
U
= 1.52ns
Example 2, F
NOM
= 25MHz
t
U
= 0.91ns
t
U
= 1.54ns
Example 3, F
NOM
= 30MHz
t
U
= 0.76ns
t
U
= 1.28ns
Example 4, F
NOM
= 40MHz
t
U
= 0.96ns
t
U
= 1.56ns
Example 5, F
NOM
= 50MHz
t
U
= 0.77ns
t
U
= 1.25ns
Example 6, F
NOM
= 80MHz
t
U
= 0.78ns
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| XRK4991ACJ-7 | 制造商:EXAR 制造商全稱:EXAR 功能描述:3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER |
| XRK4991AIJ-5 | 制造商:EXAR 制造商全稱:EXAR 功能描述:3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER |
| XRK4991AIJ-7 | 制造商:EXAR 制造商全稱:EXAR 功能描述:3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER |
| XRK4991CJ-2 | 制造商:EXAR 制造商全稱:EXAR 功能描述:3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER |
| XRK4991CJ-5 | 制造商:EXAR 制造商全稱:EXAR 功能描述:3.3V HIGH-SPEED (85 MHZ) PROGRAMMABLE SKEW CLOCK BUFFER |
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