Datasheet

SCEA019 - January 2001
7–116 Texas Instruments GTLP Frequently Asked Questions
33 What is the voltage input range I can apply to the B port if V
ref
is set at
0.8 V?
I’m using the SN74GTLP1394 to convert a 1.2-V GTL and 1.5-V CMOS signal to LVTTL.
Signal direction always is B to A. V
ref
is set at 0.8 V. I’m concerned that the 1.5-V
CMOS signal will be too high and that it will forward-bias ESD diodes on the B-port
input.
GTLP devices can be used over a range of V
TT
and V
ref
voltages and this application is
perfectly acceptable, with no danger to the ESD diodes. In the B-to-A direction, TI-OPC is
disabled and there is no restriction on V
TT
vs V
ref
if they are within data-sheet limits. In the
A-to-B direction, V
TT
vs V
ref
should be maintained at less than 0.6 V.
34 Can I use GTLP as a replacement for FB+ devices?
BTL-signal-level applications are extensions of the voltage-translation application. Normally,
GTLP devices are not compatible with FB+ devices, as shown in Figure 17. However, closer
inspection reveals that the upper and lower noise margin is about the same, and only
threshold and termination voltages are different.
GTLP
BTL
0.00 V
0.25 V
0.50 V
0.75 V
1.00 V
1.25 V
1.50 V
1.75 V
2.00 V
Upper
Noise
Margin
V
TH
Lower
Noise
Margin
Legend
V
ref
= 1.0 V
V
OH
= 1.5 V
V = 1.05 V
V
IL
= 0.95 V
V
OL
= 0.55 V
Noise margin - 400 mV
V
OH
= 2.10 V
V
IH
= 1.625 V
V
IL
= 1.475 V
V
OL
= 1.10 V
V
ref
= 1.55 V
Noise margin - 375 mV
Figure 17. Comparison of BTL to GTLP Signal Levels