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Data Sheet
January 1998
T7256 Single-Chip NT1 (SCNT1) Transceiver
102
Lucent Technologies Inc.
Questions and Answers
(continued)
Miscellaneous
(continued)
A53:
(continued)
Therefore, it is apparent that the conditions under which power is measured must be clearly specified. The
methods Lucent has used to evaluate typical and worst-case power consumption are based on our commit-
ment to provide our customers with accurate and reliable data. Measurements are performed as part of the
factory test procedure using automated test equipment. Bench top tests are performed in actual T7256-
based systems to correlate the automated test data with an actual implementation. A conservative margin is
then added to the test results for publication in our data sheets.
The following table provides power-consumption data for several scenarios so that knowledgeable customers
can fairly compare transceiver solutions. A baseline scenario is presented in the Case 1 column, and then
adders are listed in the Cases 2—6 columns to account for the worst-case condition listed in each column so
that an accurate worst-case figure can be determined based on the conditions that are present in a particular
application. Note that the tests were run at 5 V, so changes in the supply voltage will change the power
accordingly.
Table 45. Power Consumption
* Some 2B1Q silicon vendors specify power using a configuration in which the IC is active and transmitting into a 135
termination,
with no far-end transmitter attached. This configuration would cause an increase of 9 mW over the Case 1 column, instead of the
35 mW shown here. This highlights the importance of specifying measurement conditions accurately when making comparisons
between chip vendors' power numbers.
This is a worst-case number representing the state of the S/T-interface where the most +0/–0 transitions occur. In a real application,
this will be a transient state, as INFO 4 will occur as soon as synchronization is achieved. The average power consumed during a typ-
ical INFO 4, assuming a 50% mix of 1s and 0s in the B and D channels, would be approximately half this number, or 13 mW.
See the preceding table for a comparison of power dissipation with negligible capacitive loading on CKOUT. The 40 pF figure chosen
here is intended to represent a worst-case condition.
Q54:
What would cause the STLED indicator to flash sporadically at an 11 Hz rate
A54:
If the T7256 S/T-interface is operating over a long loop that is outside the range specified in the I.430/T1.605
standard, the T7256 may go into a state where it is constantly going in and out of synchronization. This
causes it to cycle between ANSI states H7 and H8, producing STLED state changes between 1 Hz flashing
and always on. When the S/T-interface loses synchronization, it takes about 96 ms before synchronization
can be reacquired. This 96 ms cycle, coupled with the STLED switching from always on to 1 Hz flashing, can
appear as 11 Hz or sporadic flashing, depending on how frequently S/T synchronization is being lost.
Variables
Baseline
Case 1
>3 kft,
26 awg
INFO 4
with all 1s
data
3-stated
Adders
Case 4
—
Case 2
0 kft*
Case 3
—
Case 5
—
Case 6
—
Loop Configuration
S/T State
—
INFO 2
—
—
—
CKOUT, MHz
(40 pF load)
Temperature (
°
C)
TDM Highway
Typical Power Consumption (mW)
—
—
15.36
—
—
25
—
—
35
—
—
26
—
—
22
85
—
5
—
Inactive
254
Active
3