MCP3464 datasheet(42/108 Pages) MICROCHIP

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MCP3461/2/4

DS20006180D-page 42

 2019-2021 Microchip Technology Inc.

5.6

ADC Output Data Format

The ADC Output Data register (ADCDATA) is located at

the address: 0x0. The default length of the register is

16-bit (15-bit + SIGN).

Output data are calculated in the digital decimation

filter with a larger resolution and are rounded to the

closest LSb value.

The rounding ensures a maximum 1/2 LSb error

instead of a simple truncation that ensures a 1 LSb

maximum error.

Equation 5-5 calculates ADC output code as a function

of the input and reference signals for DC inputs.

EQUATION 5-5:

ADC OUTPUT CODE FOR DC INPUT (DATA_FORMAT[1:0] = 00)

For AC sine wave inputs, the decimation filter transfer

function (see Equation 5-3) induces an additional gain

on the ADC output code, which depends on the input

frequency (roll-off of the decimation filter). For any

inputs, the VIN+/VIN- voltages are averaged out during

the whole conversion time, since the ADC is an

oversampling converter.

The ADC output format is set by the DATA_FORMAT[1:0]

bits in the CONFIG3 register. These bits define four

different possible formats for the ADC Data Output

MCP3461/2/4.

All possible data formats are described in Figure 5-8.

FIGURE 5-8:

ADC Output Format Selection.

When DATA_FORMAT[1:0] = 0x, the ADC resolution is

16-bit. The ADC output code is represented with MSb

first, signed two’s complement coding. With these two

data formats, the coding does not allow overrange; the

equivalent analog input range is [-VREF; +VREF – 1 LSb].

When VIN * Gain > VREF – 1 LSb, the 16-bit ADC code

(SGN + DATA[14:0]) will saturate and be locked at

0x7FFF. When VIN * Gain < -VREF, the 16-bit ADC code

will saturate and be locked at 0x8000. Using these data

formats does not permit correctly evaluating full-scale

errors in case of a positive full-scale error.

When DATA_FORMAT[1:0 = 00, the output register

shows only the 16-bit value.

When DATA_FORMAT[1:0] = 01, the output register is

32 bits long and the output code is padded with

additional zeros on the last two bytes. The output code

is left justified in this case. This format is useful for

32-bit MCU applications.

ADC_OUTPUT(LSb)

VIN+ VIN-

–

VREF+ VREF-

–

-----------------------------------------







32768 GAIN



CH_ID[3:0]

DATA[15:0]

SGN ext (12-bit)

DATA[15:0]

SGN ext (16-bit)

SGN + DATA[14:0]

0x0000

DATA_FORMAT[1:0]

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