Universal Serial Bus (USB) peripheral isolator circuit

The outer diameter of the probe domestically produced P02-T chisel head nickel-plated needle is 0.68mm. The total length of the needle is 24

Crystal Patch 2520 2.5*2.0MM 32MHZ 32.000MHZ 1.6V~3.6V Universal OSC

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:

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

2. Implement an automatic control scheme for control data streams that do not require an external control line.

3. Provide medical grade isolation.

4. Support complete peripherals to achieve USB-IF certification standards.

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

6. 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.

Circuit description

The power used by the upstream USB connector is obtained from the 5 V VBUS voltage provided by the USB cable. The peripherals must provide all the signals and pull-up/pull-down resistors that are required when the ADuM4160 is not being used. The downstream side power supply is provided by a wall power adapter and the ADP3338LDO regulator (5 V option). This LDO provides a very low dropout voltage, which reduces the regulation requirements for wall power adapters. Its small size (SOT-223) and 1 A current capability are ideal for general-purpose circuits where such peripherals may require cable power to operate.

The ADuM4160 has a variety of power, speed and protection options that must be determined. The first is the speed of the peripherals. The peripheral operates at one of three speeds: low speed (1.5 Mbps), full speed (12 Mbps), and high speed (480 Mbps). The ADuM4160 does not support high speed operation and will block the handshake signal used to negotiate this speed. The high-speed mode begins with a full-speed configuration, and the peripherals request high-speed support through a process called high-speed chirp. The ADuM4160 ignores this high-speed chirp, so high-speed running requests are never passed to the host and the peripherals continue to run at full speed.

The peripheral speed on the USB bus is either low speed or full speed. The required speed is determined by the specific peripherals, and the ADuM4160 must be set to match this speed through the state of the SPU and SPD pins. In the current schematic, the SPU and SPD pins are connected to the 3.3 V internal regulation supply VDD1 and VDD2 to set the device to run at full speed.

The 5 V supply is available on the VBUSx pin and the 3.3 V signal is generated on the VDDx pin by the internal 3.3 V regulator. Alternatively, the 3.3 V supply can be supplied to VBUSx and VDDx, and the device uses an external power supply to disable the internal regulator. This option is provided to allow the ADuM4160 to be powered from either a 5 V USB cable or a 5 V or 3.3 V rail from a peripheral. The circuit shown accepts a 5 V supply on each side and the internal regulator is active.

The ADuM4160 also provides an option to delay the application of upstream pull-up resistors under peripheral control. This feature is controlled by the PIN input. In this application, the PIN input is tied high by a jumper, so an upstream pull-up resistor is used whenever a peripheral power supply is applied. In other applications, it can be connected to the GPIO pin of a controller, can be a fixed delay circuit, or can be connected like this circuit. How you use this feature depends on the designer.

This circuit also includes a protection device. These devices are selected from manufacturers that offer a variety of different devices, and the particular device selected allows replacement with a 0 Ω short-circuit resistor to remove it from the circuit. Designers should carefully consider the choice of protection device, including the need for external protection to the need for a full set of transient suppressors and filter components. The components included in this circuit show a typical height protection configuration.

When the circuit is operating, packet inspection is performed and data is transferred from the isolated side to the other side. The data shown below shows typical full-speed processing in time domain data and eye diagrams, respectively. In real-time data, the feature to be noted is that the packet is passively idle at the beginning, it is converted to the driven J state, and the end of the packet at the end of the process is shown as a single-ended 0 state, followed by an idle J state. It is this automatic control flow and the handling of these special logic states that make the ADuM4160 chip unique on the market.