Datasheet

12
LTC1293/LTC1294/LTC1296
129346fs
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
Bipolar Transfer Curve (UNI = 0)
OUTPUT CODE
1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 0
•
•
•
1 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0
INPUT VOLTAGE
–1LSB
–2LSB
•
•
•
–(V
REF
) + 1LSB
– (V
REF
)
INPUT VOLTAGE
(V
REF
= 5V)
–0.0024V
–0.0048V
•
•
•
–4.9976V
–5.00000V
OUTPUT CODE
0 1 1 1 1 1 1 1 1 1 1 1
0 1 1 1 1 1 1 1 1 1 1 0
•
•
•
0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0
INPUT VOLTAGE
V
REF
– 1LSB
V
REF
– 2LSB
•
•
•
1LSB
0V
INPUT VOLTAGE
(V
REF
= 5V)
4.9976V
4.9851V
•
•
•
0.0024V
0V
LTC1293 AI04a
Bipolar Output Code (UNI = 0)
INPUT
CONFIGURATION UNIPOLAR MODE BIPOLAR MODE
Single-Ended Lower Value COM –(REF
+
– REF
–
) + COM
Upper Value (REF
+
– REF
–
) + COM (REF
+
– REF
–
) + COM
Differential Lower Value IN
–
–(REF
+
– REF
–
) + IN
–
Upper Value (REF
+
– REF
–
) + IN
–
(REF
+
– REF
–
) + IN
–
The following discussion will demonstrate how the two
reference pins are to be used in conjunction with the
analog input multiplexer. In unipolar mode the input span
of the A/D is set by the difference in voltage on the REF
+
pin
and the REF
–
pin. In the bipolar mode the input span is
twice the difference in voltage on the REF
+
pin and the
REF
–
pin. In the unipolar mode the lower value of the input
span is set by the voltage on the COM pin for single-ended
inputs and by the voltage on the minus input pin for
differential inputs. For the bipolar mode of operation the
voltage on the COM pin or the minus input pin set the
center of the input span.
The upper and lower value of the input span can now be
summarized in the following table:
The reference voltages REF
+
and REF
–
can fall between
V
CC
and V
–
, but the difference (REF
+
–REF
–
) must be less
than or equal to V
CC
. The input voltages must be less than
or equal to V
CC
and greater than or equal to V
–
. For the
LTC1293 REF
–
= 0V.
The following examples are for a single-ended input con-
figuration.
Example 1: Let V
CC
= 5V, V
–
= 0V, REF
+
= 4V, REF
–
= 1V
and COM = 0V. Unipolar mode of operation. The resulting
input span is 0V ≤ IN
+
≤ 3V.
1LSB
V
REF
–2LSB
V
REF
–1LSB
V
REF
V
IN
1 1 1 1 1 1 1 1 1 1 1 1
0 0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 1 1 1 1 1 1 0
0 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 0
•
•
•
1 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0
–1LSB
–2LSB
–V
REF
–V
REF
+ 1LSB
•
•
•
LTC1293 AI04b