SN74GTLPH1655

The SN74GTLPH1655 is a high-drive 16-bit universal bus transceiver (UBT) that provides LVTTL-to-GTL+ and GTL+-to-LVTTL signal-level translation. It is partitioned as two 8-bit transceivers and allows for transparent, latched, and clocked modes of data transfer similar to the '16501 function. The device provides a high-speed interface between cards operating at LVTTL logic levels and a backplane operating at GTL+ signal levels. High-speed (about two times faster than standard LVTTL or TTL) backplane operation is a direct result of GTLP's reduced output swing (<1 V), reduced input threshold levels, improved differential input, and output edge control (OEC^TM). Improved GTLP OEC circuits minimize bus settling time and have been designed and tested using several backplane models. The high drive is suitable for driving double-terminated low-impedance backplanes using incident-wave switching.

GTL+ is the Texas Instruments derivative of the Gunning transceiver logic (GTL) JEDEC standard JESD 8-3. The AC specification of the SN74GTLPH1655 is given only at the preferred higher noise margin GTL+, 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 GTL+ (V_TT = 1.5 V and V_REF = 1 V) signal levels.

Normally, the B port operates at GTL or GTL+ levels, while the A-port and control inputs are compatible with LVTTL logic levels and are 5-V tolerant. V_REF is the reference input voltage for the B port.

This SN74GTLPH1655 is fully specified for live-insertion applications using Ioff, power-up 3-state, and BIAS V_CC. 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. The BIAS V_CC circuitry precharges and preconditions the B-port input/output connections, preventing disturbance of active data on the backplane during card insertion or removal, and permits true live-insertion capability.

High-drive GTLP backplane interface devices feature 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.

Active bus-hold circuitry holds unused or undriven LVTTL inputs at a valid logic state. Use of pullup or pulldown resistors with the bus-hold circuitry is not recommended.

When VCC of the SN74GTLPH1655  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.

The SN74GTLPH1655 is characterized for operation from 40°C to 85°C.