Datasheet

SCEA019 - January 2001
Texas Instruments GTLP Frequently Asked Questions 7–93
13 How does GTLP compare to other single-ended and differential bus
solutions?
Reduced voltage swing, lower slew rate, and open-drain construction allow GTLP devices to
operate at higher frequencies than TTL devices in parallel-backplane architecture. GTLP
offers an alternative to high-data-throughput differential devices where parallel backplanes are
the best solution and higher data throughput is now required (see Table 2).
Table 2. Comparison of Single-Ended vs Differential Bus-Interface Solutions
The maximum backplane frequency is based on good backplane construction and termination
techniques. The TLK, LVDS, and SERDES data throughputs are theoretical maximum values;
actual data throughput rates are less.
Comparison of cost of GTLP versus other single-ended technologies shows that GTLP data
throughput per bit-dollar is about the same as the most popular parallel technologies, such as
ABT. Although GTLP costs about three times more than ABT, the GTLP data throughput is
more than three times greater than ABT in heavily loaded backplanes. GTLP also is an
excellent replacement for ABT or LVT in low-frequency applications where signal integrity is
an important consideration.
Strong interest in point-to-point differential-backplane connections in high-end networking and
3G wireless base-station applications has been seen, although that requires dozens to
hundreds of connections along a 19-inch backplane. Typically, telecom engineers dislike
single-ended solutions because of past EMI, maximum system frequency, and power-
consumption difficulties with older TTL solutions. The tradeoff is the ease of design of the
single-end solution versus the low EMI, higher frequency, and lower power consumption of
differential designs. GTLP provides massive throughput at lower EMI and power-consumption
levels than TTL, which is what they’re thinking of when they think single-ended. Throughput
on the backplane using GTLP devices at lower cost and without serious EMI or crosstalk
effects compares very favorably with point-to-point serial schemes.
Figure 12 allows you to pick the bus solution technology offered by TI that would be most
appropriate, based on throughput and transmission distance.
Device (typically 16245
function)
Bidirectional (B) or
Unidirectional (U)
V
CC
(V)
Tolerant to
Hot Insertion
Live Insertion
Number of Pins in the
Package
Number of Bits
Cost ($ in DGG qty 999
Internet Price)
Card Interface Drive (mA)
BP Interface Drive (mA)
I
CC
(mA - Output Low)
C
io
(pF - max)
Freq. Max BP (MHz)
Data Throughput Per
Package (Mbps -
Transparent Mode)
Data Throughput per Bit-
$ (Mbps/bit$)
Data Throughput per Bit
(Mbps/bit)
Single-Ended Bus Interface Solution
ABT
B 5 5 Y N 48 16 $1.92 -32/+64 -32/+64 32 6 -typ 33 1,056 34 66
LVT
B 3.3 5 Y N 48 16 $2.17 -32/+64 -32/+64 5 10 - typ 33 1,056 30 66
ALVT
B 3.3 5 Y N 48 16 $3.09 -32/+64 -32/+64 5 6 - typ 40 1,280 26 80
GTLP Medium Drive
B 3.3 5 Y Y 48 16 $5.00 -24/+24 50 35* 9 80 2,560 32 160
ABTE
B 5 5 Y Y 48 16 $5.01 -12/+12 -60/+90 48 8 45 1,440 18 90
BTL/FB+
B 5 5 Y Y 52 8 $10.47 -3/[phone] 100
GTLP High Drive B 3.3 5 Y Y 56 16 $5.85 -24/+24 100 35* 10 100 3,200 34 200
Differential Bus Interface Solution
ECL/PECL
U 5 5 N N 24 8 $10.20 -3/[phone]
TLK2500 B 2.5 3.3 Y N 64 16 $36.70 -1/+1 1 Serial 135 Serial 2,500 4 156
LVDS386/387 U 3.3 5 Y Y 64 16 $9.58 -8/+8 16 - Serial 70 Serial 10,080 66 630
LVDS93/94 SERDES
U 3.3 5 Y Y 64 28 $3.50 -4/+4 5 - Serial 84 Serial 1,820 19 65