Texas Instruments MSP430x1xx - Manual (Page 287)

Comparator_A in Applications
14-21
Comparator_A
Figure 14–20. Measuring the Offset Voltage of the Comparator, CAEX = 1
_
+
0
1
CAF
Set
CAIFG
τ ∼ 2 µ s
0
1
0
1
0
1
0
1
CA0
CA1
0
1
P2CA0
CAEX
Vref
P2CA1
CAON
VCC 0 V
1 0
e.g.
Capture
Input of
Timer_A
CAOUT to
External Pin
The V
offset
in this configuration is in series with V
CA0
as shown in Figure 14–21.
V
ref
= V
CA0
+ V
offset
V
CA0
= V
ref
– V
offset
Figure 14–21. Offset Voltage of the Comparator, CAEX = 1
_
+
0
1
CAF
Set
CAIFG
τ ∼
2
µ
s
0
1
CAEX
Voffset
VCA0 Vref
CAON
VCC 0 V
1 0
e.g.
Capture
Input of
Timer_A
CAOUT to
External Pin
Finally, calculate V
ref
from the below formulas.
N1 + –R
VCA0
C ln
V
ref
)
V
offset
V
CC
f
osc
N2
+
–R
VCA0
C ln
V
ref
–V
offset
V
CC
f
osc
This leads to:
V
offset
+ V
CC
e
ǒ
N1 ) N2
2 N1
ln
V
ref
V
CC
Ǔ
–V
ref
N = timer counts