MCP3903 datasheet(18/54 Pages) MICROCHIP

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MCP3903

DS25048B-page 18

Since this is the output data rate, and since the

decimation filter is a SINC (or notch) filter, there is a

notch in the filter transfer function at each integer

multiple of this rate.

The following table describes the various combinations

of OSR and PRESCALE and their associated AMCLK,

DMCLK and DRCLK rates.

4.5

OSR - Oversampling Ratio

The ratio of the sampling frequency to the output data

rate is OSR = DMCLK/DRCLK. The default OSR is 64,

or with MCLK = 4 MHz, PRESCALE = 1, AMCLK = 4

MHz, fS = 1 MHz, fD = 15.625 ksps. The following bits

in the CONFIG1 register are used to change the

oversampling ratio (OSR).

4.6

Offset Error

This is the error induced by the ADC when the inputs

are shorted together (VIN = 0V). The specification

incorporates both PGA and ADC offset contributions.

This error varies with PGA and OSR settings. The

offset is different on each channel and varies from chip

to chip. This offset error can easily be calibrated out by

a MCU with a subtraction. The offset is specified in mV.

The offset on the MCP3903 has a low temperature

coefficient, see Section 2.0 “Typical Performance

Curves”

4.7

Gain Error

This is the error induced by the ADC on the slope of the

transfer function. It is the deviation expressed in %

compared to the ideal transfer function defined by

Equation 5-3. The specification incorporates both PGA

and ADC gain error contributions, but not the VREF

contribution (it is measured with an external VREF).This

error varies with PGA and OSR settings.

The gain error on the MCP3903 has a low temperature

coefficient. See the typical performance curves for

more information.

TABLE 4-2:

DEVICE DATA RATES IN FUNCTION OF MCLK, OSR, AND PRESCALE

PRE

<1:0>

OSR <1:0>

OSR

AMCLK

DMCLK

DRCLK

(ksps)

256

MCLK/8

MCLK/32

MCLK/8192

0.4882

128

MCLK/8

MCLK/32

MCLK/4096

0.976

MCLK/8

MCLK/32

MCLK/2048

1.95

MCLK/8

MCLK/32

MCLK/1024

3.9

256

MCLK/4

MCLK/16

MCLK/4096

0.976

128

MCLK/4

MCLK/16

MCLK/2048

1.95

MCLK/4

MCLK/16

MCLK/1024

3.9

MCLK/4

MCLK/16

MCLK/512

7.8125

256

MCLK/2

MCLK/8

MCLK/2048

1.95

128

MCLK/2

MCLK/8

MCLK/1024

3.9

MCLK/2

MCLK/8

MCLK/512

7.8125

MCLK/2

MCLK/8

MCLK/256

15.625

256

MCLK

MCLK/4

MCLK/1024

3.9

128

MCLK

MCLK/4

MCLK/512

7.8125

MCLK

MCLK/4

MCLK/256

15.625

MCLK

MCLK/4

MCLK/128

31.25

Note:

For OSR = 32 and 64, DITHER = 0. For OSR = 128 and 256, DITHER = 1.

TABLE 4-3:

MCP3903 OVERSAMPLING

RATIO SETTINGS

CONFIG

OVER SAMPLING RATIO

(OSR)

OSR<1:0>

64 (DEFAULT)

128

256

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