Datasheet

SCBA015A
7–21
Fast GTLP Backplanes With the GTLPH1655
New Backplane Solution: SN74GTLPH1655 From TI
It would be ideal to have a bus concept that combines all the desirable characteristics of both
BTL and GTL. Meanwhile, TI offers a new generation of GTLP drivers that is compatible with
existing GTL systems, but provides both the advantages of BTL and also the positive aspects of
GTL drivers. A comparison is given in Table 5.
• The logic levels are compatible with GTL buses, and also bus systems with GTLP levels.
GTLP represents a modification of the GTL specification that uses different termination
voltage (V
TT
) and reference voltage (V
REF
) (see Table 6).
• Low capacitive loading of the bus (typical 6 pF)
• High drive capability (100 mA)
• Switching of a 11-Ω unidirectional line with the incident wave
• Switching of a 22-Ω bidirectional line with the incident wave
• Built-in precharge function
Table 5. SN74GTLPH1655 Compared With BTL and GTL
CHARACTERISTICS BTL GTL GTL1655
GTLP
MEDIUM
GTLP
HIGH
Supply 5 V 5 V/3.3 V 3.3 V 3.3 V
†
3.3 V
†
I
CC
120 mA 120 mA 80 mA 50 mA 40 mA
I/O capacitance <6 pF <9 pF 8 pF <9 pF <9 pF
I
OL
100 mA 40 mA 100 mA 50 mA 100 mA
Maximum power consumption per output driver 100 mW 16 mW 40 mW 20 mW 55 mW
Minimum line impedance for point-to-point connection 11 Ω 20 Ω 11 Ω 19 Ω 9.5 Ω
Minimum line-impedance bus system 22 Ω 40 Ω 22 Ω 38 Ω 19 Ω
Precharge for line insertion Yes No Yes Yes Yes
Overshoot-protection circuit No No No Yes Yes
Edge-rate control (ERC) No No Yes Yes Yes
Bus hold (A port) No Yes Yes Yes Yes
Backplane switching characteristics in data sheet No No No Yes Yes
Operational frequency on the backplane ≤30 MHz ≤40 MHz 100 MHz 100 MHz 100 MHz
†
Features 5-V tolerance at A port
The individual characteristics of the SN74GTLPH1655 are discussed in detail in the following
sections.