Circuit functions and advantages

Universal serial bus (USB) is rapidly becoming the standard interface of most PC peripherals. Because of its excellent speed, flexibility and support for device hot plug, it is replacing RS-232 and parallel printer ports. Industrial and medical equipment manufacturers also very much want to use this bus, but there is no good way to provide the necessary isolation for machine connections controlling dangerous voltages or low leakage anti defibrillation connections in medical applications, resulting in the slow popularization of applications.

The adum4160 provides an economical and simple way to implement isolation buffers for industrial and medical peripherals. Challenges to be addressed include:

Isolate directly in USB D + and D − lines to use the existing USB infrastructure in the microprocessor.

The automatic control scheme is implemented for the control data flow that does not need external control lines.

Provide medical grade isolation.

Support complete peripherals to meet usb-if certification standard.

Support full speed (12 Mbps) and low speed (1.5 Mbps) signal rates.

Support flexible power configuration.

The circuit shown in Figure 1 isolates a peripheral that supports a USB interface. Since there is no explicit definition of peripherals in this circuit, the power supply on the secondary side of the isolator has been provided as part of the solution. If the circuit is built on the PCB of the peripheral, the power can be obtained from the off-line power supply, battery or USB cable bus power supply of the peripheral, depending on the application needs.

The application circuits shown here are typical of many medical and industrial applications.

Figure 1. USB peripheral isolator circuit

Figure 1. USB peripheral isolator circuit

A photo of a typical application circuit is shown in Figure 2. The adum4160 evaluation board (left side of the photo) is connected to the 4-channel, 12 / 10 / 8-bit adcad7991 evaluation board with I 2C compatible interface. The ADC Evaluation Board acts as a peripheral and is connected to the PC through the USB port (for testing and evaluating the ADC). This provides overall isolation between the adum4160 USB port and the ADC evaluation board.

Figure 2 photo of adum4160 USB evaluation board connected to ad7991 evaluation board USB port

Figure 2 photo of adum4160 USB evaluation board connected to ad7991 evaluation board USB port

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