SLLA660 December   2024 THVD1400 , THVD2410

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Overview of RS-485
  6. 3 Shorting DE and nRE Pins
  7. 4 General R Pin Glitch Background
  8. 5 Theoretical Glitch Case for RS-485 Transceivers
  9. 6 Theoretical THVD24XX Idle Fail-safe Case
  10. 7 RS-485 Testing Setup
  11. 8 THVD1400 Capacitance Results
  12. 9 THVD2410 Capacitance Results
  13. 10Voltage Drop Workarounds
  14. 11Summary
  15. 12References

7 RS-485 Testing Setup

Both the THVD1400 and THVD2410 are tested on the setup found in Figure 7-1. For the logic side, the RXD pin has 1 kΩ resistor tied to VCC. The nRE/DE pins are connected to a 5kHz square wave to simulate the transceiver changing modes. The TXD or D pin is held at 0V. For the bus side, a 60 Ω resistor is used to simulate a load, and C1 represents the various capacitance to be tested. The R line, nRE/DE line and the differential A-B lines can be measured.

THVD 1400 and THVD2410 Setup Figure 7-1 THVD 1400 and THVD2410 Setup

Two sources of capacitance can be tested on the differential bus lines: single-ended and differential. Single-ended capacitance is where capacitors (C1 and C2) are tied from each differential bus line to ground. Differential capacitance is a single capacitor (C3) tied from line A to line B. Both setups can be tested between 50pF to 1000pF.

Single-ended and Differential Capacitance Figure 7-2 Single-ended and Differential Capacitance