MCP3425 datasheet(12/38 Pages) MICROCHIP

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MCP3425

DS22072B-page 12

4.9.2

CONVERTING THE DEVICE

OUTPUT CODE TO INPUT SIGNAL

VOLTAGE

When the user gets the digital output codes from the

device as described in Section 4.9.1 “Digital output

code from device”, the next step is converting the

digital output codes to a measured input voltage.

Equation 4-4 shows an example of converting the

output codes to its corresponding input voltage.

If the sign indicator bit (MSB) is ‘0’, the input voltage

is obtained by multiplying the output code with the LSB

and divided by the PGA setting.

If the sign indicator bit (MSB) is ‘1’, the output code

needs to be converted to two’s complement before

multiplied by LSB and divided by the PGA setting.

Table 4-4 shows an example of converting the device

output codes to input voltage.

EQUATION 4-4:

CONVERTING OUTPUT

CODES TO INPUT

VOLTAGE

TABLE 4-4:

EXAMPLE OF CONVERTING OUTPUT CODE TO VOLTAGE (WITH 16 BIT SETTING)

If MSB = 0 (Positive Output Code):

If MSB = 1 (Negative Output Code):

Where:

LSB

See Table 4-1

2’s complement

1’s complement + 1

Input Voltage

(Output Code)

LSB

PGA

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

•

Input Voltage

′s complement of Output Code)

LSB

PGA

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

•

Input Voltage

[VIN+ - VIN-] • PGA]

Digital Output Code

MSB

(sign bit)

Example of Converting Output Codes to Input Voltage

≥ V

REF

0111111111111111

14+213+212+211+210+29+28+27+26+25+24+23+22+21+20)x

LSB(

62.5 µV)/PGA = 2.048 (V) for PGA = 1

VREF - 1 LSB

0111111111111111

14+213+212+211+210+29+28+27+26+25+24+23+22+21+20)x

LSB(

62.5 µV)/PGA = 2.048 (V) for PGA = 1

2LSB

0000000000000010

(0+0+0+0+0+0+0+0+0+0+0+0+0+2

1+0)x LSB(62.5 µV)/PGA

= 125

(μV) for PGA = 1

1LSB

0000000000000001

(0+0+0+0+0+0+0+0+0+0+0+0+0+0+2

0)x LSB(62.5 µV)/PGA

62.5 (

μV)for PGA = 1

0000000000000000

(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0)x LSB(

62.5 µV)/PGA

= 0 (V) for PGA = 1

-1 LSB

1111111111111111

-(0+0+0+0+0+0+0+0+0+0+0+0+0+0+2

0)x LSB(62.5 µV)/PGA

= -

62.5 (

μV)for PGA = 1

-2 LSB

1111111111111110

-(0+0+0+0+0+0+0+0+0+0+0+0+0+2

1+0)x LSB(62.5 µV)/PGA

= - 125 (

μV)for PGA = 1

- VREF

1000000000000000

-(2

15+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0) x

LSB(

62.5 µV)/PGA = - 2.048 (V) for PGA = 1

≤ -V

REF

1000000000000000

-(2

15+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0) x

LSB(

62.5 µV)/PGA = - 2.048 (V) for PGA = 1

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