Texas Instruments MSP430x1xx - Manual (Page 284)

Comparator_A in Applications
14-18
Figure 14–14. Measuring a Current Source
_
+
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
2
1
3
3 2 1 0
CAREF
0.5 × VCC
0.25 × VCC
VCC
R(sense)
VCC
I
R(meas)
1
0
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 current I is:
I + 1
R(sense)
V
CC
ȧ
ȡ
Ȣ
1 – e
t
1
ln 0.3
t
1
) t
2
ȧ
ȣ
Ȥ
Figure 14–15. Timing for Measuring a Current Source
Phase I:
Charge-Up
Phase II:
Charge-Up:
Determine Tau, RC
t
1
t
2
Vc
V
CC
0.5
×
V
CC
I
×
R