MCP3564-ESLASHST datasheet(43/108 Pages) MICROCHIP

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DS20006181C-page 43

MCP3561/2/4

When DATA_FORMAT[1:0] = 1x, the ADC data are

represented on 25 bits. For these two data formats, the

output register is 32 bits long. With these two data

formats, the coding allows overrange; the equivalent

analog input range is [-2 x VREF, +2 x VREF – 1 LSb].

When VIN * Gain > 2VREF – 1 LSb, the 25-bit ADC code

(SGN+DATA[23:0]) will saturate and be locked at

0x0FFFFFF. When VIN * Gain < -2VREF, the 24-bit ADC

code will saturate and be locked at 0x1000000. Using

these data formats allows a correct evaluation of the

full-scale errors in case of a positive full-scale error,

since they allow inputs that can be greater than VREF or

less than -VREF.

The ADC accuracy is not maintained on the full

extended [-2 x VREF, +2 x VREF – 1 LSb] range, but only

on a smaller range, which is approximately equal to

±1.05 x VREF. This overrange can be useful in high-side

measurements and gain error cancellation algorithms.

The overrange-capable formatting on 25 bits is fully

compatible with the standard code locked formatting on

24 bits; both coding formats will produce the same

24-bit codes for the [-VREF; +VREF – 1 LSb] range and

the MSb on the 25-bit coding can be considered as a

simple Sign bit extension.

When

DATA_FORMAT[1:0]

10,

the

25-bit

(24-bit + SGN) value is right justified. The first byte of

the 32-bit ADC output code will repeat the Sign bit

(SGN).

In DATA_FORMAT[1:0] = 11, the output code is similar

to the one in DATA_FORMAT[1:0] = 10. The only differ-

ence resides in the four MSbs of the first byte, which

are no longer repeats of the Sign bit (SGN). They are

the Channel ID data (CH_ID[3:0]) that are defined in

Table 5-14. This CH_ID[3:0] word can be used to verify

that the right channel has been converted to SCAN

mode and can serve easy data retrieval and logging

(see Section 5.14 “SCAN Mode” for more details

about the SCAN mode). In MUX mode, this 4-bit word

is defaulted to ‘0000’ and does not vary with the

MUX[7:0] selection. This format is useful for 32-bit

MCU applications.

TABLE 5-7:

DATA_FORMAT[1:0] = 0x (24-BIT CODING)

Equivalent Input

Voltage

ADC Output Code (SGN + DATA[22:0])

Hexadecimal

Decimal

>VREF –1 LSb

011111111111111111111111

0x7FFFFF

+8388607

VREF –2 LSbs

011111111111111111111110

0x7FFFFE

+8388606

1LSb

000000000000000000000001

0x000001

000000000000000000000000

0x000000

-1 LSb

111111111111111111111111

0xFFFFFF

-1

-VREF + 1 LSb

100000000000000000000001

0xFFFFFF

-8388607

<-VREF

100000000000000000000000

0x800000

-8388608

TABLE 5-8:

DATA_FORMAT[1:0] = 1x (25-BIT CODING)

Equivalent Input

Voltage

ADC Output Code (SGN + DATA[21:0])

Hexadecimal

Decimal

>2 VREF –1 LSb

0111111111111111111111111

0x0FFFFFF

+16777215

2VREF –2 LSbs

0111111111111111111111110

0x0FFFFFE

+16777214

VREF +1 LSb

0100000000000000000000001

0x0800001

+8388609

VREF

0100000000000000000000000

0x0800000

+8388608

VREF –1 LSb

0011111111111111111111111

0x07FFFFF

+8388607

VREF –2 LSbs

0011111111111111111111110

0x07FFFFE

+8388606

1LSb

0000000000000000000000001

0x0000001

0000000000000000000000000

0x0000000

-1 LSb

1111111111111111111111111

0x1FFFFFF

-1

-VREF +1 LSb

1100000000000000000000001

0x1800001

-8388607

-VREF

1100000000000000000000000

0x1800000

-8388608

-VREF –1 LSb

1011111111111111111111111

0x17FFFFF

-8388609

-2VREF –1 LSb

1000000000000000000000001

0x1000001

-16777215

<-2 VREF

1000000000000000000000000

0x1000000

-16777216

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