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參數(shù)資料
| 型號： | ML65L541CK |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 總線收發(fā)器 |
| 英文描述： | 8-BIT DRIVER, TRUE OUTPUT, PDSO20 |
| 封裝： | QSOP-20 |
| 文件頁數(shù)： | 6/8頁 |
| 文件大?。?/td> | 98K |
| 代理商： | ML65L541CK |
ML65541/ML65L541
6
REV. 1.0 10/25/2000
The basic architecture of the ML65541 is shown in Figure
5. It is implemented on a 1.5m BiCMOS process.
However, in this particular circuit, all of the active
devices are NPNs — the fastest devices available in the
process.
In this circuit, there are two paths to the output. One path
sources current to the load capacitance when the signal is
asserted, and the other path sinks current from the output
when the signal is negated.
The assertion path is the emitter follower path consisting
of the level shift transistor Q1, the output transistor Q2,
and the bias resistor R8. It sources current to the output
through the 75 resistor R7 which is bypassed by another
NPN (not shown) during fast input transients. The negation
path is a current differencing op amp connected in a
follower configuration. The active components in this
amplifier are transistors Q3-Q7. R3-R6 are bias resistors,
and R1 and R2 are the feedback resistors. The key to
understanding the operation of the current differencing op
amp is to know that the currents in transistors Q3 and Q5
are the same at all times and that the voltages at the
bases of Q4 and Q6 are roughly the same. If the output is
higher than the input, then an error current will flow
through R2. This error current will flow into the base of Q6
and be multiplied by
β squared to the collector of Q7,
closing the loop. The larger the discrepancy between the
output and input, the larger the feedback current, and the
harder Q7 sinks current from the load capacitor.
A number of MOSFETs are not shown in Figure 5. These
MOSFETs are used to three-state dormant buffers. For
instance, the feedback resistors R1 and R2 were
implemented as resistive transmission gates to ensure that
disabled buffers do not load the lines they are connected
to. Similarly, there is a PMOS in series with R8 that is
normally on but shuts off for disable. Other MOSFETs
have been included to ensure that disabled buffers
consume no power.
Termination
R7 in Figure 5 also acts as a termination resistor. This 75
resistor is in series with the output and therefore helps
suppress noise caused by transmission line effects such as
reflections from mismatched impedances. System
designers using CMOS transceivers commonly have to
use external resistors in series with each transceiver
output to suppress this noise. Systems using the ML65541
or ML65L541 may not have to use these external resistors.
Applications
There are a wide variety of needs for extremely fast
buffers in high speed processor system designs like
Pentium, PowerPC, Mips, Sparc, Alpha and other RISC
processors. These applications are either in the cache
memory area or the main memory (DRAM) area. In
addition, fast buffers find applications in high speed
graphics and multimedia applications. The high
capacitive loading due to multiplexed address lines on
the system bus demand external buffers to take up the
excess drive current. The needed current to skew the
transitions between rise and fall times must be done
without adding excessive propagation delay. The
ML65541 and ML65L541 are equipped with Schottky
diodes to clean up ringing from overshoot and undershoot
caused by reflections in unterminated board traces.
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相關(guān)代理商/技術(shù)參數(shù) |
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