Datasheet

SCEA017
7–295 GTLP in BTL Applications
There are different levels of recommended I
OL
for the GTLP device at 0.4 V and 0.55 V, because
these are points on the voltage vs current (VI) curve that approximate best where the device will
be operated. The absolute I
OL
limit is twice the recommended limit. The device may
catastrophically fail at the absolute limit, and the design life of 24,000 hours is degraded on an
increasing curve as I
OL
is operated at the recommended limit, except for brief (<2 ns) time
periods where it can be operated at higher levels during ac switching. It is clear that, when using
GTLP devices at BTL levels, proper termination must be traded off against natural line
impedance without exceeding the maximum recommended I
OL
.
Frequently Asked Questions
Q: Where can I get more information on GTLP devices?
A: Visit the GTLP internet home page at www.ti.com/sc/gtlp, or e-mail the GTLP team at
[e-mail] for additional information, data sheets, simulation models, and samples.
Conclusion
GTLP can be used on new BTL/FB+ cards with only a simple modification to the V
REF
resistor
network (R/2R to R/3R) and the shift of V
TT
(1.5 V to 2.1 V) with limited performance
degradation. GTLP allows maximum system frequencies at least comparable to FB+ devices
(about 40-MHz clock), while providing advantages that include 3.3-V V
CC
with 5-V tolerance,
smaller TSSOP or BGA surface-mount packages, smaller 2-bit through larger 32-bit functions,
lower power consumption, lower cost, and an easy migration path to higher system frequencies
(up to 125 MHz) in the future, with a simple reversal of the V
REF
network to R/2R and reduction
of V
TT
to 1.5 V.
The major disadvantages are that GTLP currently is not offered in exactly the same
functionality/control or split A-port inputs and outputs as existing FB+ devices, the output
capacitance (C
io
) is larger, and R
TT
and the natural bus line impedance must be selected so that
the recommend I
OL
is not exceeded.
The GTLP Team at Texas Instruments should be contacted if there is BTL/FB+ functionality that
currently is not offered in the GTLP high-drive family.