ADN2847ACPZ-48 データシートの表示（PDF） - Analog Devices
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ADN2847ACPZ-48 Datasheet PDF : 16 Pages
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Data Sheet
REF CLOCK
20MHz TO 180MHz
CLKIN
9
1.25mA TO 20mA
21
AD9850/AD9851
AD9834
IOUT
50Ω
DDS
20
12
IOUT
RSET
50Ω
LP FILTER
(DC-COUPLED)
1/2
AD8602
10kHz TO 1MHz
35 IDTONE
0.125mA TO 2mA
BC550
ADN2847
500Ω
CONTROLLER
37.5µA TO 600µA
1/2
AD8602
BC550
50µA TO 800µA
1kΩ
32
IMMON
1.3kΩ
Figure 12. Application Circuit to Allow Fiber Identification Using the AD9850/AD9851
ADN2847
ALARM INTERFACES
The FAIL and DEGRADE outputs have an internal pull-up
resistor of 30 kΩ, used to pull the digital high value to VCC.
However, the alarm can be overdriven with an external resistor
allowing alarm interfacing to non-VCC levels. Non-VCC alarm
output levels must be below the VCC used for the ADN2847.
POWER CONSUMPTION
The ADN2847 die temperature must be kept below 125°C. Both
LFCSP packages have an exposed paddle that should be connected
in such a manner that is at the same potential as the ADN2847
ground pins. The θJA for both packages is specified in the
Absolute Maximum Ratings section. Power consumption can be
calculated using
ICC = ICCMIN + 0.3 IMOD
P = VCC × ICC + (IBIAS × V ) BIAS_PIN + IMOD (VMODP_PIN + VMODN_PIN)/2
TDIE = TAMBIENT +θJA × P
Thus, the maximum combination of IBIAS + IMOD must be
calculated, where:
ICCMIN = 50 mA (typical value of ICC provided in the
Specifications section)
IBIAS = IMOD = 0
TDIE = die temperature
TAMBIENT = ambient temperature
VBIAS_PIN = voltage at IBIAS pin
VMODP_PIN = average voltage at IMODP pin
VMODN_PIN = average voltage at IMODN pin
LASER DIODE INTERFACING
Many laser diodes designed for 2.5 Gbps operation are packaged
with an internal resistor to bring the effective impedance up to
25 Ω to minimize transmission line effects. In high current
applications, the voltage drop across this resistor combined
with the laser diode forward voltage makes direct connection
between the laser and the driver impractical in a 3 V system.
AC coupling the driver to the laser diode removes this
headroom constraint.
Caution must be taken when choosing component values for
ac coupling (see Figure 15) to ensure that the time constants
(L/R and RC) are sufficiently long for the data rate and expected
number of consecutive identical digits (CIDs). Failure to do this
can lead to pattern dependent jitter and vertical eye closure.
For designs with low series resistance, or where external
components become impractical, the ADN2847 supports direct
connection to the laser diode (see Figure 14). In this case, care
must be taken to ensure that the voltage drop across the laser
diode does not violate the minimum compliance voltage on the
IMODP pin.
OPTICAL SUPERVISOR
The PSET and ERSET potentiometers can be replaced with a
dual-digital potentiometer, the ADN2850 (see Figure 13). The
ADN2850 provides an accurate digital control for the average
optical power and extinction ratio and ensures excellent
stability over temperature.
VCC
VCC
Tx
Rx
CLK
CS
ADN2850
SDI
SDO
DAC1
CLK
CS
DAC2
IMPD
ADN2847
IMODP
IBIAS
PSET
ERSET
VCC
VCC
RZ
DATAP
DATAN
IDTONE
Figure 13. Application Using the ADN2850 a Dual 10-Bit Digital
Potentiometer with an Extremely Low Temperature Coefficient
as an Optical Supervisor
Rev. B | Page 11 of 16
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