參數(shù)資料
型號(hào)： AD9548BCPZ
廠商： Analog Devices Inc
文件頁(yè)數(shù)： 33/112頁(yè)
文件大?。?/td> 0K
描述： IC CLOCK GEN/SYNCHRONIZR 88LFCSP
產(chǎn)品變化通告： AD9548 Mask Change 20/Oct/2010
標(biāo)準(zhǔn)包裝： 1
類型： 時(shí)鐘/頻率發(fā)生器，同步器
PLL： 是
主要目的： 以太網(wǎng)，SONET/SDH，Stratum
輸入： CMOS，LVDS，LVPECL
輸出： CMOS，LVDS，LVPECL
電路數(shù)： 1
比率 - 輸入:輸出： 1:1
差分 - 輸入:輸出： 是/是
頻率 - 最大： 750kHz
電源電壓： 1.71 V ~ 3.465 V
工作溫度： -40°C ~ 85°C
安裝類型： 表面貼裝
封裝/外殼： 88-VFQFN 裸露焊盤(pán)，CSP
供應(yīng)商設(shè)備封裝： 88-LFCSP-VQ（12x12）
包裝： 托盤(pán)
Data Sheet
AD9548
Rev. E | Page 27 of 112
REFERENCE CLOCK INPUTS
Four pairs of pins provide access to the reference clock receivers.
Each pair is configurable either as a single differential receiver
or as two independent single-ended receivers. To accommodate
input signals with slow rising and falling edges, both the
differential and single-ended input receivers employ hysteresis.
Hysteresis also ensures that a disconnected or floating input
does not cause the receiver to oscillate spontaneously.
When configured for differential operation, the input receivers
accommodate either ac- or dc-coupled input signals. The
receiver is internally dc biased in order to handle ac-coupled
operation.
When configured for single-ended operation, the input
receivers exhibit a pull-down load of 45 k (typical). Three user
programmable threshold voltage ranges are available for each
single-ended receiver.
REFERENCE MONITORS
The reference monitors depend on a known and accurate
system clock period. Therefore, the functioning of the reference
monitors is not reliable until the system clock is stable. To avoid
an incorrect valid indication, the reference monitors indicate
fault status until the system clock stability timer expires (see the
Reference Period Monitor
Each reference input has a dedicated monitor that repeatedly
measures the reference period. The AD9548 uses the reference
period measurements to determine the validity of the reference
based on a set of user provided parameters in the profile
register area of the register map (see the Profile Registers
also uses the reference period monitor to assign a particular
reference to a profile when the user programs the device for
automatic profile assignment.
The monitor works by comparing the measured period of a
particular reference input with the parameters stored in the
profile register assigned to that same reference input. The
parameters include the reference period, an inner tolerance, and
an outer tolerance. A 50-bit number defines the reference
period in units of femtoseconds. The 50-bit range allows for a
reference period entry of up to 1.125 sec. However, an actual
reference signal with a period in excess of 1 sec is beyond the
recommended operating range of the device. A 20-bit number
defines the inner and outer tolerances. The value stored in the
register is the reciprocal of the tolerance specification. For
example, a tolerance specification of 50 ppm yields a register
value of 1/(50 ppm) = 1/0.000050 = 20,000 (0x04E20).
The use of two tolerance values provides hysteresis for the
monitor decision logic. The inner tolerance applies to a
previously faulted reference and specifies the largest period
tolerance that a previously faulted reference can exhibit before it
qualifies as nonfaulted. The outer tolerance applies to an already
nonfaulted reference. It specifies the largest period tolerance
that a nonfaulted reference can exhibit before being faulted.
To produce decision hysteresis, the inner tolerance must be less
than the outer tolerance. That is, a faulted reference must meet
tighter requirements to become nonfaulted than a nonfaulted
reference must meet to become faulted.
Reference Validation Timer
Each reference input has a dedicated validation timer. The
validation timer establishes the amount of time that a
previously faulted reference must remain fault free before the
AD9548 declares it nonfaulted. The timeout period of the
validation timer is programmable via a 16-bit register (see the
validation register contained within each of the eight profile
registers in the register map, Address 0x0600 to Address
0x07FF). The 16-bit number stored in the validation register
represents units of milliseconds, which yields a maximum
timeout period of 65,535 ms.
Note that a validation period of 0 must be programmed to
disable the validation timer. With the validation timer disabled,
the user must validate a reference manually via the force
validation timeout register (Address 0x0A0E).
Reference Redetect Timer
Each reference input has a dedicated redetect timer. The
redetect timer is useful only with the device programmed for
automatic profile selection. The redetect timer establishes the
amount of time that a reference must remain faulted before the
AD9548 attempts to reassign it to a new profile. The timeout
period of the redetect timer is programmable via a 16-bit
register (see the redetect timeout register contained within each
of the eight profile registers in the register map, Address 0x0600
to Address 0x07FF). The 16-bit number stored in the redetect
timeout register represents units of milliseconds, which yields a
maximum timeout period of 65,535 ms.
Note that a timeout period of 0 must be programmed to disable
the redetect timer.
Reference Validation Override Control
Register 0x0A0E to Register 0x0A10 provide the user with the
ability to override the reference validation logic enabling a
certain level of troubleshooting capability. Each of the eight
input references has a dedicated block of validation logic as
shown in Figure 35. The state of the valid signal at the output is
what defines a particular reference as valid (1) or not (0), which
includes the validation period (if activated) as prescribed by the
validation timer. The override controls are the three control bits
on the left side of the diagram.
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