參數(shù)資料
型號: ACS8946T
廠商: Semtech
文件頁數(shù): 4/40頁
文件大?。?/td> 0K
描述: IC JITTER ATT MULT PLL 48-QFN
標準包裝: 1
類型: 時鐘/頻率發(fā)生器,多路復(fù)用器
PLL:
主要目的: 以太網(wǎng),SONET/SDH
輸入: LVPECL
輸出: CML,LVPECL
電路數(shù): 1
比率 - 輸入:輸出: 2:4
差分 - 輸入:輸出: 是/是
頻率 - 最大: 625MHz
電源電壓: 3.135 V ~ 3.465 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 48-VFQFN 裸露焊盤
供應(yīng)商設(shè)備封裝: 48-QFN(7x7)
包裝: 托盤
ADVANCED COMMUNICATIONS
FINAL
DATASHEET
Revision 3/November 2006 Semtech Corp.
Page 12
www.semtech.com
ACS8946 JAM PLL
such that if any phase error signal is present, the LOCKB
output drives out a +10
A current, otherwise it is off.
Consequently this output (LOCKB) is a pulse width
modulated (PWM) pulse stream whose mark/space ratio
indicates the current input phase error. Filtering this
signal with a simple external RC parallel filter as shown in
Figure 9 will give a signal whose output level indicates PLL
phase and frequency lock.
Figure 9 Lock Filter Components
The filtering components are external so that the time to
indicate lock or not locked can be optimized for the
application. The output indicates both phase and
frequency lock. During off-frequency conditions the
LOCKB output will be predominately high in its PWM
generation with the filtered version giving a constant high
state.
PLL Bandwidth Setting
The bandwidth is set by two identical sets of passive RC
components that connect to the differential charge pump
outputs and internal VCO control inputs. Pins VCN and
VCP are the combined differential charge pump outputs
and VCO control voltage inputs. Figure 10 shows the
arrangement.
Figure 10 Loop Filter Components
All capacitors should be low leakage and low ESR
(Equivalent Series Resistance). Tantalum, or ceramic
where possible, are suitable. Tables 6 to 9 are based on a
damping factor of 1.2 (phase margin 80.2°). Higher
damping factors may be used if lower transfer peaking is
required. Contact Semtech Sales Support for further
details.
RC Components Required to Achieve Bandwidth at
Given Input Frequencies (Tables 6 to 9).
Note...* not available at 155.52 MHz input
Note...All bandwidths are subject to ± 20% variation due to
component tolerancing.
LOCKB
JA
M
P
L
R1
470K
LOCK_B
C1
220nF
GND
F8944_011Lockfilter_02
VCP
VCN
JA
M
P
L
C1
R1
R2
C3
C4
GND
C2
F8943_010Loopfilter_02
Table 6 77.76 MHz or 19.44 MHz Input Frequency
Bandwidth
R1 & R2/
C2 & C4/
F
C1 & C3
nF
Closed Loop
1500
56
33
200
2000
75
15
100
4000
150
4.7
33
8000
270
0.68
7.5
Table 7 155.52 MHz or 38.88 MHz Input Frequency
Bandwidth
R1 & R2/
C2 & C4/
F
C1 & C3
nF
Closed Loop
1500*
110
15
91
2000
150
6.8
47
4000
300
2.2
15
8000
560
0.47
3.9
Table 8 125 MHz Input Frequency
Bandwidth
R1 & R2/
C2 & C4/
F
C1 & C3
nF
Closed Loop
1500
68
22
150
2000
91
15
91
4000
180
3.3
20
8000
360
0.68
6.2
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