The SN74GTLP817 is a medium-drive fanout driver that provides LVTTL-to-GTLP and GTLP-to-LVTTL
signal-level translation. The device provides a high-speed interface between cards operating at LVTTL logic
levels and a backplane operating at GTLP signal levels. High-speed (about three times faster than standard
TTL or LVTTL) backplane operation is a direct result of GTLP reduced output swing (<1 V), reduced input
threshold levels, improved differential input, and OEC circuitry. The improved GTLP OEC circuitry minimizes
bus settling time and has been designed and tested using several backplane models. The medium drive allows
incident-wave switching in heavily loaded backplanes with equivalent load impedance down to 19 . BO1 and
BO2 can be tied together to drive an equivalent load impedance down to 11 .
GTLP is the Texas Instruments (TI) derivative of the Gunning Transceiver Logic (GTL) JEDEC standard
JESD 8-3. The ac specification of the SN74GTLP817 is given only at the preferred higher noise-margin GTLP,
but the user has the flexibility of using this device at either GTL (VTT = 1.2 V and V REF = 0.8 V) or GTLP
(VTT = 1.5 V and VREF = 1 V) signal levels.
Normally, the B port operates at GTLP signal levels. The A-port and control inputs operate at LVTTL logic levels
but are 5-V tolerant and are compatible with TTL and 5-V CMOS inputs. VREF is the B-port differential input
GNDT is the TTL output ground, while GNDG is the GTLP output ground, and both may be separated from each
other for a quieter device.
This device is fully specified for hot-insertion applications using Ioff and power-up 3-state. The Ioff circuitry
disables the outputs, preventing damaging current backflow through the device when it is powered down. The
power-up 3-state circuitry places the outputs in the high-impedance state during power up and power down,
which prevents driver conflict.
This device features adjustable edge-rate control (ERC). Changing the ERC input voltage between GND and
VCC adjusts the B-port output rise and fall times. This allows the designer to optimize system data-transfer rate
and signal integrity to the backplane load. ERC automatically is selected to the same speed as alternate source
1-to-6 fanout drivers that use pin 18 for 3.3-V or 5-V VCC .
When VCC is between 0 and 1.5 V, the device is in the high-impedance state during power up or power down.
However, to ensure the high-impedance state above 1.5 V, the output-enable (OE\) input should be tied to VCC
through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of