MCP3422A1-E/MS Microchip Technology, MCP3422A1-E/MS Datasheet - Page 15

• Manufacturer Part Number: MCP3422A1-E/MS
• Description: 18-Bit, Multi-Channel Delta-Sigma ADC w/ I2C Interface and On-Board Reference ; 8L MSOP 3x3mm
• Manufacturer: Microchip Technology

4.9
4.9.1
The digital output code is proportional to the input volt-
age and PGA settings. The output data format is a
binary two’s complement. With this code scheme, the
MSB can be considered a sign indicator. When the
MSB is a logic ‘0’, the input is positive. When the MSB
is a logic ‘1’, the input is negative. The following is an
example of the output code:
(a) for a negative full-scale input voltage: 100...000
(b) for a zero differential input voltage: 000...000
(c) for a positive full-scale input voltage: 011...111
The MSB (sign bit) is always transmitted first through
the I
sion is 18, 16, 14, or 12 bits depending on the conver-
sion rate selection bit settings by the user.
The output codes will not roll-over even if the input volt-
age exceeds the maximum input range. In this case,
the code will be locked at 0111...11 for all voltages
greater than (V
voltages less than -V
example of output codes of various input levels for 18
bit conversion mode.
minimum and maximum output codes for each conver-
sion rate option.
The number of output code is given by:
EQUATION 4-2:
The LSB of the data conversion is given by:
EQUATION 4-3:
© 2008 Microchip Technology Inc.
Number of Output Code =
Where:
Where:
2
Example: (CHn+ - CHn-)
=
Example: (CHn+ - CHn-)
Example: (CHn+ - CHn-) = 0
C serial data line. The resolution for each conver-
See
N
(
Maximum Code
Digital Output Codes and
Conversion to Real Values
Table 4-3
DIGITAL OUTPUT CODE FROM
DEVICE
=
LSB
REF
Resolution, which is programmed in
the Configuration Register.
=
- 1 LSB)/PGA and 1000...00 for
2 V
--------------------- -
for Maximum Code
×
Table 4-3
REF
2
+
N
REF
1
/PGA.
) PGA
×
=
•
•
PGA = -2.048V
PGA = 2.048V
2 2.048V
--------------------------
shows an example of
×
Table 4-2
×
2
(
---------------------------------------- -
N
CHn+ CHn-
2.048V
–
shows an
)
Table 4-1
setting. The measured unknown input voltage is
obtained by multiplying the output codes with LSB. See
the following section for the input voltage calculation
using the output codes.
TABLE 4-1:
TABLE 4-2: EXAMPLE OF OUTPUT CODE
TABLE 4-3:
Note 1:
Resolution
Note:
[CHn+ - CHn-] • PGA
Setting
Resolution Setting
12
14
16
18
Input Voltage:
2:
V
REF
shows the LSB size of each conversion rate
< -V
-1 LSB
-2 LSB
≥
- V
2 LSB
1 LSB
MSB is a sign indicator:
0: Positive input (CHn+ > CHn-)
1: Negative input (CHn+ < CHn-)
Output data format is binary two’s
complement.
Maximum n-bit code = 2
Minimum n-bit code = -1 x 2
V
12 bits
14 bits
16 bits
18 bits
- 1 LSB
0
REF
REF
REF
Data Rate
FOR 18 BITS (NOTE 1, NOTE 2)
3.75 SPS
240 SPS
60 SPS
15 SPS
RESOLUTION SETTINGS VS.
LSB
MINIMUM AND MAXIMUM
OUTPUT CODES (NOTE)
MCP3422/3/4
Minimum
011111111111111111
011111111111111111
000000000000000010
000000000000000001
000000000000000000
111111111111111111
111111111111111110
100000000000000000
100000000000000000
-131072
-32768
-2048
-8192
Code
Digital Output Code
1 mV
250 µV
62.5 µV
15.625 µV
N-1
DS22088B-page 15
- 1
N-1
LSB
Maximum
131071
32767
Code
8191
2047