Microchip Technology MCP3421EV Data Sheet
MCP3421
DS22003E-page 14
© 2009 Microchip Technology Inc.
4.9.2
CONVERTING THE DEVICE
OUTPUT CODE TO INPUT SIGNAL
VOLTAGE
OUTPUT CODE TO INPUT SIGNAL
VOLTAGE
When the user gets the digital output codes from the
device as described in
device as described in
code from device”, the next step is converting the
digital output codes to a measured input voltage.
digital output codes to a measured input voltage.
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.
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.
needs to be converted to two’s complement before
multiplied by LSB and divided by the PGA setting.
shows an example of converting the device
output codes to input voltage.
EQUATION 4-4:
CONVERTING OUTPUT
CODES TO INPUT
VOLTAGE
CODES TO INPUT
VOLTAGE
TABLE 4-4:
EXAMPLE OF CONVERTING OUTPUT CODE TO VOLTAGE (WITH 18 BIT SETTING)
If MSB = 0 (Positive Output Code):
If MSB = 1 (Negative Output Code):
Where:
LSB
=
2’s complement
=
1’s complement + 1
Input Voltage
(Output Code)
LSB
PGA
------------
•
=
Input Voltage
(2
′
s complement of Output Code)
LSB
PGA
------------
•
=
Input Voltage
[V
IN
+ - V
IN
-]
•
PGA]
Digital Output Code
MSB
(sign bit)
Example of Converting Output Codes to Input Voltage
≥ V
REF
011111111111111111
0
(2
16
+2
15
+2
14
+2
13
+2
12
+2
11
+2
10
+2
9
+2
8
+2
7
+2
6
+2
5
+2
4
+2
3
+2
2
+
2
1
+2
0
)x LSB(15.625
μV)/PGA = 2.048 (V) for PGA = 1
V
REF
- 1 LSB
011111111111111111
0
(2
16
+2
15
+2
14
+2
13
+2
12
+2
11
+2
10
+2
9
+2
8
+2
7
+2
6
+2
5
+2
4
+2
3
+2
2
+
2
1
+2
0
)x LSB(15.625
μV)/PGA = 2.048 (V) for PGA = 1
2 LSB
000000000000000010
0
(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+2
1
+0)x
LSB(15.625
μV)/PGA = 31.25 (μV) for PGA = 1
1 LSB
000000000000000001
0
(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+2
0
)x
LSB(15.625
μV)/PGA = 15.625 (μV)for PGA = 1
0
000000000000000000
0
(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0)x
LSB(15.625
μV)/PGA = 0 V (V) for PGA = 1
-1 LSB
111111111111111111
1
-(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+2
0
)x
LSB(15.625
μV)/PGA = - 15.625 (μV)for PGA = 1
-2 LSB
111111111111111110
1
-(0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+2
1
+0)x
LSB(15.625
μV)/PGA = - 31.25 (μV)for PGA = 1
- V
REF
100000000000000000
1
-(2
17
+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0) x
LSB(15.625
μV)/PGA = - 2.048 (V) for PGA = 1
≤ -V
REF
100000000000000000
1
-(2
17
+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0+0) x
LSB(15.625
μV)/PGA = - 2.048 (V) for PGA = 1