Output Interfacing
(Continued)
may be used. The resistive divider network provides 75Ω ter-
mination and establishes proper ECL levels. This circuit con-
sumes slightly more power than the previous circuits.
Cable
Length
100 meters
200 meters
300 meters
R Value
(Ohms)
15000
20000
32000
For example, a C
AEC
value of 100 pF results in an adaptive
loop time constant of 2 µs at 200 meters of cable.
CONNECTION AND OPERATION OF CD AND MUTE
DS100056-27
FIGURE 7. Alternative Load Terminated
Output Interface
Design Guidelines
SELECTING THE AUTOMATIC EQUALIZER CAPACITOR
The AEC capacitor sets the loop time constant
τ
for the
equalizer’s adaptive loop response time. The following for-
mula is used to set the loop time constant:
τ
= R
•
C
AEC
•
10
−6
R is a conversion factor that is set by internal equalizer pa-
rameters and cable length. For Belden 8281 coaxial cable,
the R values are (τ = µs, C
AEC
in pF):
Carrier Detect (CD)
is a CMOS output that indicates the
presence of equalized data from the filter. This CD output
can be connected to MUTE to suspend changes in the data
outputs DO and DO, if no valid signal exists. This simple
configuration prevents random output transitions due to
noise. For sparse transition patterns it is recommended that
a capacitor be connected to CD as shown in
Figure 1.
Add a capacitor to pin 5 to slow the response time of Carrier
Detect when Carrier Detect is connected to MUTE. The ca-
pacitor reduces sensitivity to pathological patterns. Patho-
logical patterns are defined as sparse data sequences with
few transitions.
OUTPUT EYE MONITOR OEM CONNECTIONS
The OEM is a high-speed, buffered output for monitoring the
equalized eye pattern prior to the output comparator. Its out-
put is designed to drive an AC-coupled 50Ω coaxial cable
with a series 50Ω backmatch resistor. The cable should be
terminated with 50Ω at the oscilloscope.
Figure 1
shows a
schematic with a typical connection.
MINIMUM DATA TRANSITIONS
The CLC014 specifies a minimum transition rate. For the
CLC014 this sets the minimum data rate for transmitting data
through any cable medium. The CLC014 minimum average
transition density is found in the Electrical Characteristics
section of the datasheet.
POWER SUPPLY OPERATION AND THERMAL
CONSIDERATIONS
The CLC014 operates from either +5V or −5.2V single sup-
plies. Refer to
Figure 1
when operating the part from +5V.
When operating with a −5.2V supply, the V
EE
pins should be
bypassed to ground. The evaluation board and associated
literature provide for operation from either supply.
Maximum power dissipation occurs at minimum cable
length. Under that condition, I
CC
= 58 mA.
Total power dissipated:
P
T
= (58 mA)(5V) = 290 mW
Power in the load:
P
L
= (0.7V)(11 mA) + (37.5)(11 mA)
2
= 12 mW
Maximum power dissipated on the die:
P
DMAX
= P
T
–P
L
= 278 mW
Junction Temperature =
(θ
JA
)(278 mW) + T
A
= T
A
+ 26˚C
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