
Comparator_A in Applications
14-18
Figure 14–14. Measuring a Current Source
_
+
0
1
CAF
Set
CAIFG
τ ∼ 2 µs
0
1
0
1
0
1
0
1
CA0
CA1
0
1
P2CA0
P2CA1
VCAREF
CARSEL
0
2
1
3
3 2 10
CAREF
0.5 × V
CC
0.25 × V
CC
V
CC
R
(sense)
VCC
I
R
(meas)
1
0
CAEX
CAON
V
CC
0 V
1
0
CAON
V
CC
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
1
–e
t
1
ln
0.3
t
1
t
2
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
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