The SN74GTLP1395 is two 1-bit, high-drive, 3-wire bus transceivers that provide LVTTL-to-GTLP and GTLP-to-LVTTL signal-level translation for applications, such as primary and secondary clocks, that require individual output-enable and true/complement controls. The device allows for transparent and inverted transparent modes of data transfer with separate LVTTL input and LVTTL output pins, which provide a feedback path for control and diagnostics monitoring. The device provides a high-speed interface between cards operating at LVTTL logic levels and a backplane operating at GTLP signal levels and is designed especially to work with the Texas Instruments 3.3-V 1394 backplane physical-layer controller. High-speed (about three times faster than standard LVTTL or TTL) backplane operation is a direct result of GTLP reduced output swing (<1 V), reduced input threshold levels, improved differential input, OEC circuitry, and TI-OPC circuitry. Improved GTLP OEC and TI-OPC circuitry minimizes bus settling time, and have been designed and tested using several backplane models. The high drive allows incident-wave switching in heavily loaded backplanes, with equivalent load impedance down to 11 .
GTLP is the Texas Instruments derivative of the Gunning Transceiver Logic (GTL) JEDEC standard JESD 8-3. The ac specification of the SN74GTLP1395 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 VREF = 0.8 V) or GTLP (VTT = 1.5 V and VREF = 1 V) signal levels. For information on using GTLP devices in FB+/BTL applications, refer to TI application reports, _Texas Instruments GTLP Frequently Asked Questions_, literature number SCEA019, and _GTLP in BTL Applications_, literature number SCEA017.
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 or 5-V CMOS devices. VREF is the B-port differential input reference voltage.
This device is fully specified for live-insertion applications using Ioff, power-up 3-state, and BIAS VCC. 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 VCC 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.
This GTLP device features TI-OPC circuitry, which actively limits the overshoot caused by improperly terminated backplanes, unevenly distributed cards, or empty slots during low-to-high signal transitions. This improves signal integrity, which allows adequate noise margin to be maintained at higher frequencies.
High-drive GTLP backplane interface devices feature adjustable edge-rate control (ERC). Changing the ERC input voltage between low and high 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.
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 the driver.
TI-OPC Circuitry Limits Ringing on Unevenly Loaded Backplanes
OEC Circuity Improves Signal Itegrity and Reduces Electromagnetic Interference
Bidirectional Interface Between GTLP Signal Levels and LVTTL Logic Levels
Split LVTTL Port Provides a Feedback Path for Control and Diagnostics Monitoring
LVTTL Interfaces Are 5-V Tolerant
High-Drive GTLP Outputs (100 mA)
LVTTL Outputs (24 mA/24 mA)
Variable Edge-Rate Control (ERC) Input Selects GTLP Rise and Fall Times for Optimal Data-Transfer Rate and Signal Integrity in Distributed Loads
Ioff, Power-Up 3-State, and BIAS VCC Support Live Insertion
Polarity Control Selects True or Complementary Outputs
Latch-Up Performance Exceeds 100 mA Per JESD 78, Class II
ESD Protection Exceeds JESD 22
2000-V Human-Body Model (A114-A)
200-V Machine Model (A115-A)
1000-V Charged-Device Model (C101)
OEC and TI-OPC are trademarks of Texas Instruments.
