MCP4017 datasheet(33/66 Pages) MICROCHIP

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DS22147A-page 33

MCP4017/18/19

5.0

SERIAL INTERFACE -

I2C MODULE

A 2-wire I2C serial protocol is used to write or read the

digital potentiometer’s wiper register. The I2C protocol

utilizes the SCL input pin and SDA input/output pin.

The I2C serial interface supports the following features.

• Slave mode of operation

• 7-bit addressing

• The following clock rate modes are supported:

- Standard mode, bit rates up to 100 kb/s

- Fast mode, bit rates up to 400 kb/s

• Support Multi-Master Applications

The serial clock is generated by the Master.

The I2C Module is compatible with the Phillips I2C

specification. Phillips only defines the field types, field

lengths, timings, etc. of a frame. The frame content

defines the behavior of the device. The frame content

for the MCP4017, MCP4018, and MCP4019 devices

are defined in this section of the Data Sheet.

Figure 5-1 shows a typical I2C bus configurations.

FIGURE 5-1:

Typical Application I2C Bus

Configurations.

Refer to Section 2.0 “Typical Performance Curves”,

AC/DC Electrical Characteristics table for detailed input

threshold and timing specifications.

5.1

I2C I/O Considerations

I2C specifications require active low, passive high

functionality on devices interfacing to the bus. Since

devices may be operating on separate power supply

sources, ESD clamping diodes are not permitted. The

specification recommends using open drain transistors

tied to VSS (common) with a pull-up resistor. The

specification makes some general recommendations

on the size of this pull-up, but does not specify the

exact value since bus speeds and bus capacitance

impacts the pull-up value for optimum system

performance.

Common pull-up values range from 1 kΩ to a max of

~10 kΩ. Power sensitive applications tend to choose

higher values to minimize current losses during

communication but these applications also typically

utilize lower VDD.

The SDA and SCL float (are not driving) when the

device is powered down.

A "glitch" filter is on the SCL and SDA pins when the pin

is an input. When these pins are an output, there is a

slew rate control of the pin that is independent of device

frequency.

5.1.1

SLOPE CONTROL

The device implements slope control on the SDA

output. The slope control is defined by the fast mode

specifications.

For Fast (FS) mode, the device has spike suppression

and Schmidt trigger inputs on the SDA and SCL pins.

Single I2C Bus Configuration

Host

Controller

Device 1

Device 3

Device n

Device 2

Device 4

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