MCP3423 Ver la hoja de datos (PDF) - Microchip Technology

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MCP3423

18-Bit, Multi-Channel ΔΣ Analog-to-Digital Converter with I2C™ Interface and On-Board Reference

Microchip Technology 

MCP3422/3/4

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

If MSB = 0 (Positive Output Code):

Input Voltage

=

(Output

Code)

•

-L----S---B---

PGA

If MSB = 1 (Negative Output Code):

Input Voltage =

(2′s complement of Output Code)

• -L----S----B--

PGA

Where:

LSB = See Table 4-1

2’s complement = 1’s complement + 1

TABLE 4-4: EXAMPLE OF CONVERTING OUTPUT CODE TO VOLTAGE (WITH 18 BIT SETTING)

Input Voltage

[CHn+ - CHn-] • PGA]

Digital Output Code

MSB

Example of Converting Output Codes to Input Voltage

≥ VREF

VREF - 1 LSB

2 LSB

1 LSB

011111111111111111 0 (216+215+214+213+212+211+210+29+28+27+26+25+24+23+22+21+20)

x LSB(15.625μV)/PGA = 2.048 (V) for PGA = 1

011111111111111111 0 (216+215+214+213+212+211+210+29+28+27+26+25+24+23+22+21+20)

x LSB(15.625μV)/PGA = 2.048 (V) for PGA = 1

000000000000000010 0 (0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+21+0)x LSB(15.625μV)/PGA

= 31.25 (μV) for PGA = 1

000000000000000001 0 (0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+20)x LSB(15.625μV)/PGA

= 15.625 (μV)for PGA = 1

0

-1 LSB

-2 LSB

- VREF

≤ -VREF

000000000000000000 0 (0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0)x LSB(15.625μV)/PGA

= 0 V (V) for PGA = 1

111111111111111111 1 -(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+20)x LSB(15.625μV)/PGA

= - 15.625 (μV)for PGA = 1

111111111111111110 1 -(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+21+0)x LSB(15.625μV)/PGA

= - 31.25 (μV)for PGA = 1

100000000000000000 1 -(217+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0) x

LSB(15.625μV)/PGA = - 2.048 (V) for PGA = 1

100000000000000000 1 -(217+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0) x

LSB(15.625μV)/PGA = - 2.048 (V) for PGA = 1

DS22088C-page 16

© 2009 Microchip Technology Inc.

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