参数资料
| 型号： | AD9551BCPZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 10/40页 |
| 文件大小： | 0K |
| 描述： | IC CLOCK GEN MULTISERV 40-LFCSP |
| 标准包装： | 1 |
| 类型： | 时钟发生器 |
| PLL： | 是 |
| 输入： | 晶体 |
| 输出： | CMOS，LVDS，LVPECL |
| 电路数： | 1 |
| 比率 - 输入:输出： | 2:2 |
| 差分 - 输入:输出： | 是/是 |
| 频率 - 最大： | 900MHz |
| 除法器/乘法器： | 无/无 |
| 电源电压： | 3.3V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 40-VFQFN 裸露焊盘，CSP |
| 供应商设备封装： | 40-LFCSP-VQ（6x6） |
| 包装： | 托盘 |
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AD9551
Rev. B | Page 18 of 40
The reference DLL measures the period of the active reference
and produces the required N/2 delay value. When the reference
DLL locks, the following three events occur:
Both DLL A and DLL B are enabled.
The DLL associated with the active reference enters open-
loop mode.
The DLL associated with the alternate reference enters
closed-loop mode.
This implies that the signal driving the input PLL is the active
reference (after division by its input divider) with a half-cycle delay.
Because the alternate DLL is in closed-loop mode, and assuming
that the alternate reference is available, the output of the alternate
DLL is edge-aligned with the delayed output of the active DLL.
Furthermore, the closed-loop operation of the alternate DLL
causes its delay value to be adjusted dynamically so that it main-
tains nominal edge alignment with the output of the active DLL.
Edge alignment of the active and alternate references is the key
to the hitless switchover capability of the AD9551.
Reference Switchover and Holdover Mode
If the reference monitor detects the loss of the active reference,
it initiates the following three simultaneous operations:
The output mux selects the output of the alternate DLL.
The alternate DLL holds its most recent delay setting (that
is, the delay setting that edge-aligned the output of the alter-
nate DLL with the output of the active DLL). Note that this
operation ensures hitless switching between references.
The new active reference is connected to the reference DLL
to measure its period (that is, a new N/2 value).
Because the failed alternate reference is assigned to the alternate
DLL, upon its return the alternate DLL (which is in closed-loop
mode) automatically edge-aligns the delayed alternate reference
with the delayed active reference. Thus, if the new active reference
fails, switchover to the alternate reference occurs in a hitless
manner. This method of swapping the functionality of DLL A
and DLL B as either active (open-loop) or alternate (closed-loop)
allows for continuous hitless switching from one reference to
the other, as needed (assuming the availability of an alternate
reference upon failure of the active reference).
Note that if both references fail, the device enters holdover
mode. In this case, the reference monitor holds the DCXO at its
last setting prior to the holdover condition, and the DCXO free
runs at this setting until the holdover condition expires.
Forcing Selection of the Active Reference
Because the synchronization mechanism autonomously switches
between references, the user has no way of knowing which
reference is currently the active reference. However, the device
can be forced to select a specific input reference as the active
reference. For example, to force REFA to be the active reference,
power down the REFB input receiver by programming the appro-
priate registers (or disconnect the REFB signal source).
The absence of a REFB signal causes the device to perform
a hitless switchover to REFA. If REFA is already the active
reference, the absence of REFB results in no action, and REFA
remains the active reference. In this way, the user can ensure
that REFA is the active reference. Likewise, by using the same
procedure but reversing the roles of the two references, the user
can force the device to select REFB as the active reference.
Digitally Controlled Crystal Oscillator (DCXO)
The DCXO is the fundamental building block of the input PLL
(see the Input PLL section). The DCXO relies on an external
crystal (19.44 MHz to 52 MHz) as its frequency source. The
resonant frequency of the external crystal varies as a function
of the applied load capacitance. The AD9551 has two internal
capacitor banks (static and dynamic) that provide the required
load capacitance. In operation, the control loop of the input PLL
automatically adjusts the value of the capacitive load to push or
pull the crystal resonant frequency over a small range of approxi-
mately ±50 ppm.
The tuning capacitor bank sets the static load capacitance, which
defaults to ~2 pF. The varactor bank is a dynamic capacitance
controlled by the DCXO to push or pull the crystal resonant
frequency. The nominal varactor capacitance is ~6 pF, and
when combined with the 2 pF static capacitance and 2 pF of
typical parasitic capacitance, the total crystal load capacitance is
~10 pF (default).
The user can alter the default load capacitance by changing
the static load capacitance of the tuning capacitor bank via
Register 0x1B[5:0]. These six bits set the static load capacitance
in 0.25 pF increments up to a maximum of ~16 pF.
The control loop of the input PLL locks the DCXO to the active
reference signal by dynamically controlling the varactor capaci-
tance. Note that the narrow frequency control range (±50 ppm) of
the varactor bank, combined with the default operating parameters
of the AD9551, dictate the use of a crystal with specified load
capacitance of 10 pF and a frequency tolerance of 20 ppm (see
the NDK NX3225SA, for example).
The narrow tuning range of the DCXO has two implications.
First, the user must properly choose the divide ratio of the input
reference divider to establish a frequency that is within the DCXO
tuning range. Second, the user must ensure that the jitter/wander
of the input reference is low enough to ensure the stability of the
input PLL control loop for applications where the DCXO is the
reference source for the output PLL (the default configuration).
Normally, the input SDMs help to mitigate the input jitter because
of the way they interact with the behavior of the input PLL. Input
jitter becomes an issue, however, when the input dividers operate
in integer-only mode or the input PLL is bypassed.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AD9551BCPZ-REEL7 | 功能描述:IC CLOCK GEN TRANSLATOR 40LFCSP RoHS:是 类别:集成电路 (IC) >> 时钟/计时 - 时钟发生器，PLL，频率合成器 系列:- 标准包装:2,000 系列:- 类型:PLL 时钟发生器 PLL:带旁路 输入:LVCMOS，LVPECL 输出:LVCMOS 电路数:1 比率 - 输入:输出:2:11 差分 - 输入:输出:是/无 频率 - 最大:240MHz 除法器/乘法器:是/无 电源电压:3.135 V ~ 3.465 V 工作温度:0°C ~ 70°C 安装类型:表面贴装 封装/外壳:32-LQFP 供应商设备封装:32-TQFP（7x7） 包装:带卷 (TR) |
| AD9552 | 制造商:AD 制造商全称:Analog Devices 功能描述:Oscillator Frequency Upconverter |
| AD9552/PCBZ | 功能描述:BOARD EVALUATION FOR AD9552 RoHS:是 类别:编程器，开发系统 >> 评估演示板和套件 系列:- 标准包装:1 系列:PSoC® 主要目的:电源管理，热管理 嵌入式:- 已用 IC / 零件:- 主要属性:- 次要属性:- 已供物品:板，CD，电源 |
| AD9552BCPZ | 功能描述:IC PLL CLOCK GEN LP 32LFCSP RoHS:是 类别:集成电路 (IC) >> 时钟/计时 - 时钟发生器，PLL，频率合成器 系列:- 标准包装:2,000 系列:- 类型:PLL 频率合成器 PLL:是 输入:晶体 输出:时钟 电路数:1 比率 - 输入:输出:1:1 差分 - 输入:输出:无/无 频率 - 最大:1GHz 除法器/乘法器:是/无 电源电压:4.5 V ~ 5.5 V 工作温度:-20°C ~ 85°C 安装类型:表面贴装 封装/外壳:16-LSSOP（0.175"，4.40mm 宽） 供应商设备封装:16-SSOP 包装:带卷 (TR) 其它名称:NJW1504V-TE1-NDNJW1504V-TE1TR |
| AD9552BCPZ | 制造商:Analog Devices 功能描述:IC PLL CLOCK GENERATOR 112.5MHZ LFCSP-32 |
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