The power supply tests include testing to measure the variation of the 5-V supply when the input voltage (VDC) varies, and measuring the input current when input voltage is negative with respect to GND, which mimics a reverse input condition.

Figure 3-17 shows that the 5-V supply is active and well regulated for input voltages on VDC in the range of 2 V to 36 V. These measurements are recorded with no external load on the reference design board.

Figure 3-2 Measured 5-V Supply vs Applied Input Voltage

Figure 3-3 shows the input current under conditions of negative voltages applied to input with respect to GND. For applied voltages more negative than –5 V, the current increases linearly.

Figure 3-3 Input Current vs Applied Negative Input Voltage

For positive (normal polarity) applied Input voltages, Figure 3-4 shows the input current at input versus the applied input voltage. For a nominal 24-V supply level, the design has an input current of around 120 mA, including the controlCARD microcontroller board. This represents the idle current when no relay is actively driven, the CAN, RS-485, daisy chain, and Ethernet transceiver are idle. As the applied voltage is increased to 36 V, there is a slight increase in the input current, but no significant increase. This indicates there is no breakdown of any of the components connected to VDC, thus the design is not damaged by steady-state VDC voltages up to 36 V. The design is robust to load-dump conditions that can occur on the supply system.

Figure 3-4 Input Current vs Applied Positive Input Voltage