10.2.1 Design Requirements

This device uses Schottky transistor logic technology. Take care to avoid bus contention because it can drive currents that would exceed maximum limits. The high drive creates fast edges into light loads, so routing and load conditions must be considered to prevent ringing.

10.2.2 Detailed Design Procedure

• Power Supply
  • Each device must maintain a supply voltage between 4.5 V and 5.5 V
• Inputs
  • Input signals must meet the V_IH and V_IL specifications in Electrical Characteristics
  • Inputs leakage values (I_I, I_IH, I_IL) from Electrical Characteristics must be considered
• Outputs
  • Output signals are specified to meet the V_OH and V_OL specifications in Electrical Characteristics as a minimum (the values could be closer to V_CC for high signals or GND for low signals)
  • TI recommends maintaining output currents as specified in Recommended Operating Conditions
  • The part can be damaged by sourcing or sinking too much current. See Electrical Characteristics for details.

10.2.3 Application Curve

It is common to see significant losses in ribbon cables and back planes. Figure 6 shows a simplified simulation of a ribbon cable from a 5-V, 10-MHz low-drive strength source. It shows the difference between an input signal from a weak driver like an MCU or FPGA compared to a strong driver like the SN74LS245 when measured at the distant end of the cable. By adding a high-current drive transceiver before the cable, the signal strength can be significantly improved, and subsequently the cable can be longer.

Unbuffered line is directly connected to low current source, SN74LS245 line is buffered through the transceiver. Both signals are measured at the distant end of the ribbon cable. Input signal is not shown.

Figure 6. Simulated Outputs From Ribbon Cable With a 5-V, 10-MHz Source