Datasheet

7–210
1 ns Minimum
2.1 V
1 V
Low-to-High and High-to-Low Transition
Figure 2. Slew-Rate Control (OEC) Diagram
Table 1 shows an evolutionary progression in bipolar wafer-fab technology and improved propagation-delay performance.
Bipolar fab technologies are chosen for this class of device for their high drive capability, low switching noise, and relative ease
of designing (relative to pure CMOS) the analog circuitry required to meet the slew-rate control requirement (see Figure 2).
Bipolar circuits have the disadvantage of relatively high power dissipation. The heat generated by this high power dissipation,
coupled with the large switching currents coming from the bus termination, place a thermal limitation on the numbers of bits that
can be integrated into a single, standard integrated-circuit package (typically, only four bits).
Table 1. BTL/Futurebus Transceiver Offering Available Today
TRANSCEIVER SUPPLIER TECHNOLOGY BITS/PACKAGE t
pd
(ns)
ALS056/057 TI, NSC 3-µm Bipolar 4/8 20
DS3890 NSC 2-µm Bipolar 8
†
15
DS3896/7 NSC 1.5-µm Bipolar 4/8 12
DS3893A NSC 1.2-µm Bipolar 4 7
FB1650 TI 0.8-µm BiCMOS 18 7.2
FB1651 TI 0.8-µm BiCMOS 17 7.2
FB1653 TI 0.8-µm BiCMOS 17 6.6
FB2032 TI 0.8-µm BiCMOS 9 8.3
FB2033A TI 0.8-µm BiCMOS 8 5.6
FB2031 TI, Philips 0.8-µm BiCMOS 9 6.6
FB2040 TI, Philips 0.8-µm BiCMOS 8 6.5
FB2041A TI, Philips 0.8-µm BiCMOS 7 5.6
†
Unidirectional driver only; not a true bidirectional transceiver
The newer class of BiCMOS transceivers employs a bipolar output structure to achieve the desired drive, noise, and slew-rate
control of previous-generation products. They also offer higher performance, much lower power dissipation, and take the next
step toward higher integration.
Futurebus adds an additional constraint to board layout by mandating that all compliant cards have a maximum stub length of
25 mm to reduce loading and minimize reflections. This is also a wise rule of thumb for non-BTL/Futurebus designs. As data
paths have increased in width from 32 to 64 bits (128 bits in the future), this stub-length requirement has forced system designers
to wrestle with the manufacturing problems of double-sided surface mounting of the transceivers on boards as large as 12
Standard Units (12SU). Even with the relatively dense packaging of today’s fastest and most integrated transceivers, this can be
a formidable design problem that adds significantly to the overall manufacturing cost of a board (see Figure 3).