SN74GTLP817

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 (V_TT = 1.2 V and V _REF = 0.8 V) or GTLP (V_TT = 1.5 V and V_REF = 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. V_REF is the B-port differential input reference voltage.

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 I_off and power-up 3-state. The I_off 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 V_CC 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 V_CC .

When V_CC 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 V_CC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.