MCP3461RT-ESLASHST datasheet(49/118 Pages) MICROCHIP

49 / 118 page

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DS20006404C-page 49

MCP3461/2/4R

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

represented on 17 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 17-bit ADC code

(SGN + DATA[15:0]) will saturate and be locked at

0x0FFFF. When VIN * Gain < -2VREF, the 16-bit ADC

code will saturate and be locked at 0x10000. 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 17 bits is fully

compatible with the standard code locked formatting on

16 bits; both coding formats will produce the same

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

the MSb on the 17-bit coding can be considered as a

simple Sign bit extension.

When

DATA_FORMAT[1:0]

10,

the

17-bit

(16-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 5-15. 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 5.15 “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 (16-BIT CODING)

Equivalent Input Voltage

ADC Output Code

(SGN + DATA[14:0])

Hexadecimal

Decimal

> VREF –1 LSb

0111111111111111

0x7FFF

+32767

VREF –2 LSbs

0111111111111110

0x7FFE

+32766

1LSb

0000000000000001

0x0001

0000000000000000

0x0000

-1 LSb

1111111111111111

0xFFFF

-1

-VREF +1 LSb

1000000000000001

0xFFFF

-32767

< -VREF

1000000000000000

0x8000

-32768

TABLE 5-8:

DATA_FORMAT[1:0] = 1x (17-BIT CODING)

Equivalent Input Voltage

ADC Output Code

(SGN + DATA[15:0])

Hexadecimal

Decimal

> 2 VREF –1 LSb

01111111111111111

0x0FFFF

+65535

2VREF –2 LSbs

01111111111111110

0x0FFFE

+65534

VREF +1 LSb

01000000000000001

0x08001

+32769

VREF

01000000000000000

0x08000

+32768

VREF –1 LSb

00111111111111111

0x07FFF

+32767

VREF – 2 LSbs

00111111111111110

0x07FFE

+32766

1LSb

00000000000000001

0x00001

00000000000000000

0x00000

-1 LSb

11111111111111111

0x1FFFF

-1

-VREF +1 LSb

11000000000000001

0x18001

-32767

-VREF

11000000000000000

0x18000

-32768

-VREF –1 LSb

10111111111111111

0x17FFF

-32769

-2 VREF +1 LSb

10000000000000001

0x10001

-65535

< -2 VREF

10000000000000000

0x10000

-65536

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