Datasheet

"#$$%
SBOS301A − MAY 2004 − REVISED MARCH 2007
www.ti.com
12
Q
1
R
REF
1.62M
Ω
+2.5V
4
1
5
3
15
13
12
16
V
−
Com
Q
2
V
1
867
+5V
I
2
I
1
I
µ
A
REF3040
or
REF3240
4.096V
Reference
10
µ
F
+
1000pF
Input current
from photodiode
Photodiode
(4)
or current source
R
1
R
2
R
5
100k
Ω
R
7
100k
Ω
R
8
316k
Ω
R
6
66.5k
Ω
R
3
R
4
V
O4
(3)
−
IN
4
+IN
4
V
LOGOUT
(2)
+IN
5
−
IN
5
V
O5
V
CM IN
(1)
I
1
V
REF
2.5V
REF
V
REF GND
A
3
A
1
A
2
A
4
A
5
I
2
LOG114
1110
9
V
Com
= +2.5V
NOTE: (1) In single−supply configuration, V
CM IN
must be connected to
≥
1V.
(2) V
LOGOUT
= 0.375
×
log(I
1
/I
2
)+2.5V.
(3) V
O4
=
−
0.249
×
log(I
1
/I
2
)+1.5V.
(4) The cathode of the photodiode is returned to V
REF
resultinginzerobiasacrossit.Thecathode
could be returned to a voltage more positive than V
CM IN
to create a reverse bias for reducing
photodiode capacitance, which increases speed.
Figure 2. Single-Supply Configuration Example for Measurement Over Eight Decades.