MCP3221 datasheet(14/26 Pages) MICROCHIP

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MCP3221

DS21732B-page 14

 2003 Microchip Technology Inc.

4.5

Differential Non-Linearity (DNL)

In the ideal A/D converter transfer function, each code

has a uniform width. That is, the difference in analog

input voltage is constant from one code transition point

to the next. Differential nonlinearity (DNL) specifies the

deviation of any code in the transfer function from an

ideal code width of 1 LSB. The DNL is determined by

subtracting the locations of successive code transition

points after compensating for any gain and offset

errors. A positive DNL implies that a code is longer than

the ideal code width, while a negative DNL implies that

a code is shorter than the ideal width.

4.6

Integral Non-Linearity (INL)

Integral nonlinearity (INL) is a result of cumulative DNL

errors and specifies how much the overall transfer

function deviates from a linear response. The method

of measurement used in the MCP3221 A/D converter

to determine INL is the “end-point” method.

4.7

Offset Error

Offset error is defined as a deviation of the code transi-

tion points that are present across all output codes.

This has the effect of shifting the entire A/D transfer

function. The offset error is measured by finding the dif-

ference between the actual location of the first code

transition and the desired location of the first transition.

The ideal location of the first code transition is located

at 1/2 LSB above VSS.

4.8

Gain Error

The gain error determines the amount of deviation from

the ideal slope of the A/D converter transfer function.

Before the gain error is determined, the offset error is

measured and subtracted from the conversion result.

The gain error can then be determined by finding the

location of the last code transition and comparing that

location to the ideal location. The ideal location of the

last code transition is 1.5 LSBs below full-scale or VDD.

4.9

Conversion Current (IDD)

The average amount of current over the time required

to perform a 12-bit conversion.

4.10

Active Bus Current (IDDA)

The average amount of current over the time required

to monitor the I2C bus. Any current the device con-

sumes while it is not being addressed is referred to as

“Active Bus” current.

4.11

Standby Current (IDDS)

The average amount of current required while no con-

version is occurring and while no data is being output

(i.e., SCL and SDA lines are quiet).

4.12

I2C Standard Mode Timing

I2C specification where the frequency of SCL is

100 kHz.

4.13

I2C Fast Mode Timing

I2C specification where the frequency of SCL is

400 kHz.

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