ESD (Electrostatic Discharge) Precautions. MCC MIIC-203

If you are connecting the I 2 C adapter to a 3.3 volt target system, you should follow these steps BEFORE applying power:

• Shut off the iPort/USB internal pull-ups (See Pull-up Resistor section). Use external pull-ups to the target system’s 3.3V power. These pull-ups may already be present in the target system.

• Disconnect the I 2 C Bus connector +5V wire from the target system. The iPort/USB will be powered from the USB, and the target system will be powered by its own 3.3V power supply.

The I 2 C adapter is a 5-volt device. Any signal at or above 3.3V on the SCL, SDA, and /INT lines is high enough for the adapter to see a Logical 1.

3.3

Connecting to an SMBus Target System

If you are connecting the I 2 C adapter to a SMBus target system, you should follow these steps BEFORE applying power:

• Shut off the iPort/USB internal pull-ups (See Pull-up Resistor section).

• Use external SMBus rated (appoximately15k ohms) pull-up resistors. These pull-ups may already be present in the target system.

• Visit our I

2

C versus SMBus FAQ page (www.mcc-us.com/I2CSMBusFAQ.htm).

• See the SMBus Specification for additional details.

Special Note for SMBus Users: MCC’s I 2 C adapters are designed to be I 2 C Bus compatible, not SMBus compatible. Some features of the SMBus protocol not supported include time-outs, device reset, and Packet Error Check byte processing.

The non-supported SMBus features may, or may not, permit the use of the I 2 C adapter in your SMBus application. Consult the MCC FAQ web page and SMBus

Specification for details.

4 ESD (Electrostatic Discharge) Precautions

Electrostatic discharge is defined as the transfer of charge between bodies at different electrical potentials. Electrostatic discharge can change the electrical characteristics of a semiconductor device, degrading or destroying it. Electrostatic discharge also may upset the normal operation of an electronic system, causing equipment malfunction or failure.

When connecting the I 2 C adapter to a host computer and a target system, extreme

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care must be taken to avoid electrostatic discharge. Failure to follow ESD protection procedures when using the I 2 C adapter could damage the host computer, I 2 C adapter, or the target system, and void product warranty coverage.

4.1

Host Computer Grounding

Case 1 - Desktop and Single-board Computers. The chassis on a desktop or single-board host computer must be connected to earth ground to comply with safety regulations. If the computer chassis is NOT connected to earth ground for some reason (i.e., use of a two-prong power mains plug), the host computer power supply ground will float to some unknown voltage potential.

Case 2 - Laptop Computers. Laptop computers present special ESD problems. Most laptop computers use an external double-insulated mains power supply which is

NOT connected to the mains earth ground. This means that the laptop chassis is floating at some unknown voltage potential.

In either case, upon connection to the I 2 C adapter and the target system, the host computer will discharge energy through its serial port to the I 2 C adapter, and on to the target system. This discharge could damage the host computer, I 2 C adapter, and the target system.

4.2

Grounding Solutions

To avoid damage to the host computer, I 2 C adapter, or target system, follow these instructions:

• Wear an earth grounded wrist strap, or discharge any static charge build-up, when handling the I 2 C adapter or any target system devices.

• Ensure that both the host computer and target system are connected to a common earth ground point.

• Make sure that all interconnections are made BEFORE applying power to the host computer, I

2 C adapter, and target system.

• If you are using a laptop computer or host computer that is NOT connected to mains earth ground, make a hard-wired connection from the host computer (i.e., port connector shell) and the target system ground connector to a common earth ground point.

• Avoid plugging and unplugging system components while the host computer or target system is powered.

• Ensure that any devices connected to the target system are properly grounded to

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