lt1293 Linear Technology Corporation, lt1293 Datasheet - Page 12

• Manufacturer Part Number: lt1293
• Description: Single Chip 12-bit Data Acquisition System
• Manufacturer: Linear Technology Corporation

LTC1293/LTC1294/LTC1296
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
and the REF
twice the difference in voltage on the REF
REF
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:
12
A
PPLICATI
–
pin. In the unipolar mode the lower value of the input
–
pin. In the bipolar mode the input span is
O
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
U
OUTPUT CODE
S
•
•
•
I FOR ATIO
U
INPUT VOLTAGE
V
V
W
REF
REF
1LSB
0V
– 1LSB
– 2LSB
•
•
•
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 1
0 1 1 1 1 1 1 1 1 1 1 0
+
Bipolar Output Code (UNI = 0)
Bipolar Transfer Curve (UNI = 0)
pin and the
INPUT VOLTAGE
U
•
•
•
(V
4.9976V
4.9851V
0.0024V
REF
0V
+
•
•
•
= 5V)
pin
1 1 1 1 1 1 1 1 1 1 1 1
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
1 1 1 1 1 1 1 1 1 1 1 0
1 0 0 0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0 0 1
INPUT
CONFIGURATION
Single-Ended
Differential
The reference voltages REF
V
than or equal to V
or equal to V
LTC1293 REF
The following examples are for a single-ended input con-
figuration.
Example 1: Let V
and COM = 0V. Unipolar mode of operation. The resulting
input span is 0V ≤ IN
OUTPUT CODE
CC
and V
•
•
•
•
•
•
–
, but the difference (REF
Lower Value COM
Upper Value (REF
Upper Value (REF
Lower Value IN
CC
–
INPUT VOLTAGE
–(V
= 0V.
and greater than or equal to V
REF
– (V
CC
CC
–2LSB
–1LSB
) + 1LSB
•
•
•
REF
. The input voltages must be less than
= 5V, V
+
)
UNIPOLAR MODE
≤ 3V.
–
+
+
INPUT VOLTAGE
– REF
– REF
–
+
(V
–5.00000V
–0.0024V
–0.0048V
–4.9976V
= 0V, REF
REF
and REF
–
–
•
•
•
= 5V)
) + COM (REF
) + IN
LTC1293 AI04a
+
–REF
–
LTC1293 AI04b
–
+
BIPOLAR MODE
–(REF
–(REF
(REF
can fall between
= 4V, REF
–
) must be less
+
+
+
+
V
– REF
– REF
IN
– REF
– REF
–
. For the
–
–
) + COM
) + IN
–
–
–
) + COM
) + IN
129346fs
= 1V
–
–