Use digital isolators as level shifters in non-isolated applications

iCoupler digital isolators are widely used to transmit digital signals across the isolation barrier. In some cases, digital isolators are also very useful in non-isolated applications.

–48V DC-DC Power Supply

In communication power applications, the standard rail is –48V DC and the primary control signal is referenced to that rail. The secondary side control signal is typically a ground referenced low voltage I/O (eg, +5V, +3.3V CMOS). The primary and secondary sides are connected and the entire system is non-isolated. In this type of DC-DC power supply application, the digital isolator is suitable for level shifting of the feedback signal. As shown in Figure 1, the high-level input voltage of the secondary side is 5V, and the low-level voltage is 0V; the high-level voltage of the primary side is –43V, and the low level is –48V. The primary side of the digital isolator is connected to the –48V rail and the VDD supply is connected to –43V. Due to the built-in isolation barrier, each side of the isolator operates in a separate voltage domain, providing level shifting. The iCoupler digital isolator also protects the secondary circuit from faults such as overvoltage or short circuit.

Figure 1 -48V to 5vDC-DC power supply with feedback based on digital isolator

Multiple power system

For systems with multiple power domains, there may be one or more power supplies in the off state and other power supplies in the active state. In this case, if there is any data line connection between the two power supply regions, the shutdown region may be parasiticly powered by the voltage or current on the data line. Figure 2 shows this application.

Leakage current between two power domains

To avoid leakage current, the digital line must be set to low output or high impedance mode. When using the iCoupler digital isolator instead of the two power domains for direct connection, the leakage current between them can be blocked (Figure 3). Since there is no need to control the output state at this time, the hardware and software protection design can be simplified.

Connect two power zones using a digital isolator

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