Universal Serial Bus (USB) Peripheral Isolator Circuit Diagram

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Circuit function and advantage

The Universal Serial Bus (USB) is quickly becoming the standard interface for most PC peripherals. It is replacing RS-232 and parallel printer ports because of its speed, flexibility, and support for hot swapping of devices. Industrial and medical device manufacturers are also eager to use this bus, but suffer from a lack of good ways to provide the necessary isolation for machine connections that control dangerous voltages or low-leakage anti-defibrillation connections in medical applications, leading to slow application adoption. .

The ADuM4160 provides an economical and simple way to implement industrial and medical peripheral isolation buffers. The challenges that need to be addressed include:

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

An automatic control scheme is implemented for control data streams that do not require an external control line.

Provide medical grade isolation.

Support complete peripherals to meet USB-IF certification standards.

Full speed (12 Mbps) and low speed (1.5 Mbps) signal rates are supported.

Support flexible power configuration.

The circuit shown in Figure 1 isolates a peripheral that supports the USB interface. Since this circuit does not have a well-defined peripheral, the power supply to the secondary side of the isolator is already available as part of the solution. If the circuit is built on the peripheral's PCB, the power supply can be obtained from the peripheral's off-line power, battery, or USB cable bus power, depending on the application.

The application circuit shown here is a typical circuit for many medical and industrial applications.

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 an evaluation board for a 4-channel, 12/10/8-bit ADCAD7991 with an I 2 C-compatible interface. The ADC evaluation board acts as a peripheral and connects to the PC via a USB port (to test and evaluate the ADC). This provides overall isolation between the ADuM4160 USB port and the ADC evaluation board.

Figure 2 Photo of the ADuM4160 USB Evaluation Board connected to the USB port of the AD7991 EV kit