Texas Instruments MSP430x1xx - Manual (Page 285)

Comparator_A in Applications
14-19
Comparator_A
Figure 14–16. A/D Converter for Voltage Sources
_
+
0
1
CAF
Set
CAIFG
τ ∼
2
µ
s
0
1
0
1
0
1
0
1
CA0
CA1
0
1
P2CA0
P2CA1
VCAREF
CARSEL
0
1
2
3
3 2 1 0
CAREF
0.5
×
VCC
0.25 × VCC
R2
VCC
1
0
V(meas)
R1
C
CAEX CAON
VCC 0 V
1 0
CAON
VCC 0 V
1 0
e.g.
Capture
Input of
Timer_A
CAOUT to
External Pin
The equation for the voltage V
meas
is:
V(meas)
+ R1
)
R2
R2
V
CC
ȧ
ȡ
Ȣ
1 –e
t
1
ln 0.3
t
1
) t
2
ȧ
ȣ
Ȥ
Figure 14–17. A/D Converter for Voltage Sources, Conversion Timing
Phase I:
Charge-Up
Phase II:
Charge-Up:
Determine Tau, RC
t
1
t
2
Vc
V
CC
0.5
×
V
CC
V
R
Note: During phase I, control bit P2CA0 = 1 and CAREF = 0.
During phase II, control bit P2CA0 = 0, CARSEL = 0, and CAREF= 1.