參數(shù)資料
型號(hào)： T7264
英文描述： T7264 U-Interface 2B1Q Transceiver
中文描述： T7264 U型接口2B1Q收發(fā)器
文件頁(yè)數(shù)： 51/54頁(yè)
文件大小： 876K
代理商： T7264
Lucent Technologies Inc.
51
Data Sheet
April 1998
T7264 U-Interface 2B1Q Transceiver
Appendix A. Questions and Answers
(continued)
Q60
: In the idle mode, when afrst or
RESET
is active,
the current increases from 6 mA (powerdown
mode) to 40 mA—50 mA (normal mode). Is this
proper behavior for the T7264 Also, is this a cor-
rect interpretation of the data sheet description of
idle mode (page 10, third paragraph)
A60
: This behavior is proper for the T7264. The reason
more current is needed in the reset state (i.e.,
RESET
pin or afrst bit active) is that much of the
analog circuitry (line driver, band gap voltage ref-
erences, A/D, and D/A) is powered down during
the idle state, but is active during the reset state.
Notice that idle and reset are two different states:
reset state overrides idle when the RESET pin or
afrst is active. The reset state is normally a tran-
sient state which only lasts a short time, unless
the reset function is being constantly asserted.
This means that
RESET
should not be used indis-
criminately as part of a general start-up proce-
dure. The meaning of the third paragraph on
page 10 in the data sheet is that at the end of a
RESET
condition, the transceiver will change to
the idle state (only momentarily if a start-up
request is being made via the istp bit or a far-end
wakeup tone). In this way, the data sheet is con-
sistent with these results.
Q61
: Can you provide detailed information on the
active power consumption of the T7264
A61
: When discussing active power measurement
figures, it is important to note that the conditions
under which power measurements are made are
not always completely stated by 2B1Q integrated
circuit vendors. For example, loop length is not
typically mentioned in regard to power dissipa-
tion, yet power dissipation on a short loop is
noticeably greater than on a long loop. There are
two reasons for the increased power dissipation
at shorter loop lengths:
1. The overall loop impedance is smaller, requir-
ing a higher current to drive the loop.
2. The far-end transceiver is closer, requiring the
near-end transceiver to sink more far-end cur-
rent in order to maintain virtual ground at its
transmitter outputs.
The lab measurements in the following table pro-
vide examples of how power dissipation varies
with loop length for a specific T7264 with its
15.36 MHz CKOUT output enabled and driving
40 pF (see the next table below for information on
CKOUT). Note that power dissipation with a zero
length loop (the worst-case loop) is about 35 mW
higher than a loop of >3 kft length. Thus, loop
length needs to be considered when determining
worst-case power numbers.
* This is the configuration used in Method B discussed on the
next page.
Also, in the case of the T7264, the use of the out-
put clock CKOUT (pin 23) must be considered
since its influence on power dissipation is signifi-
cant. Some applications may make use of this
clock, while others may leave it 3-stated. The
power dissipation of CKOUT is as follows:
The methods used to evaluate typical and worst-
case power consumption are based on Lucent’s
commitment to provide its customers with accu-
rate and reliable data. Measurements are per-
formed as part of the factory test procedure using
automated test equipment. Bench top tests are
performed in actual ISDN systems to correlate
the automated test data with a typical implemen-
tation. A conservative margin is then added to the
test results for publication in the data sheets.
Loop Configuration
18 kft/26 AWG
6 kft/26 AWG
3 kft/26 AWG
2 kft/26 AWG
1 kft/26 AWG
0.5 kft/26 AWG
0 kft
135
load, ILOSS or lpbk
active, no far-end transceiver*
Power (mW)
273
273
277
280
288
296
308
281.5
CKOUT
Frequency
(MHz)
15.36
10.24
7.68
Power Due to
CKOUT 40 pF
Load (mW)
21.3
17.7
12.6
Power Due to
CKOUT No
Load (mW)
11.0
9.1
6.6
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