Datasheet
SCBA015A
7–23
Fast GTLP Backplanes With the GTLPH1655
SN74GTLPH1655: Link Between a GTLP Backplane and an LVTTL Module
The SN74GTLPH1655 converts LVTTL-level signals (A port) into GTL- or GTLP-level signals
(B port), and
vice versa
. The user decides, by choosing the termination voltage and the
reference voltage, which level will be provided on the B-port side (see Table 6). The A port is, in
every case, compatible with LVTTL.
This conversion is useful when continuing to work with LVTTL levels on the module, while the
GTL and GTLP levels, specially developed for this application, are transmitted on the backplane.
The low-voltage TTL and GTLP signal levels are shown in Figure 13. The SN74GTLPH1655
needs 3.3 V as the operating voltage.
A-Port LVTTL Levels B-Port GTL/GTLP Levels
V
CC
= 3.0 V to 3.6 V
V
OH
min = 2.2 V
V
IH
min = 2.0 V
V
TH
= 1.5 V
V
IL
max = 0.8 V
V
OL
max = 0.55 V
V
CC
= 3.0 V to 3.6 V
V
REF
(GTLP) = 1.0 V
V
REF
(GTL) = 0.8 V
V
OH
= V
TT
(via pullup)
V
TT
(GTLP) = 1.5 V
V
TT
(GTL) = 1.2 V
V
IH
min = V
REF
+ 50 mV
V
IL
max = V
REF
– 50 mV
V
OL
max = 0.5 V
Figure 13. LVTTL and GTLP Signal Levels of SN74GTLPH1655
Table 6. Choice of GTL/GTLP Level (Using V
TT
and V
REF
)
LEVEL MIN TYP MAX UNIT
GTL
V
TT
1.14 1.2 1.26
V
GTL
V
REF
0.74 0.8 0.87
V
GTLP
V
TT
1.35 1.5 1.65
V
GTLP
V
REF
0.87 1 1.1
V