LT1789-1/LT1789-10
18
1789fc
BLOCK DIAGRAM
Figure 1. Block Diagram
Setting the Gain
The gain of the LT1789-1 and LT1789-10 is set by the
value of resistor R
G
, applied across pins 1 and 8. For the
LT1789-1, the gain G will be:
G = 1+ 200k/R
G
and R
G
can be calculated from the desired gain by
R
G
= 200k/(G – 1)
For the LT1789-10, the gain G will be
G =10 • (1 + 200k/R
G
)
and R
G
can be calculated from the desired gain by
R
G
= 200k/(0.1 • G – 1)
For the lowest achievable gain, R
G
may be set to infinity
by leaving Pins 1 and 8 open.
Input and Output Offset Voltage
The offset voltage of the LT1789-1/LT1789-10 has two
components: the output offset and the input offset. The
total offset voltage referred to the input (RTI) is found by
dividing the output offset by the programmed gain (G) and
adding it to the input offset. At high gains the input offset
voltage dominates, whereas at low gains the output offset
voltage dominates. The total offset voltage is:
Total input offset voltage (RTI)
= input offset + (output offset/G)
Total output offset voltage (RTO)
= (input offset • G) + output offset
–
+
3
1
A1
V
–
V
–
+IN
R
G
V
+
V
+
V
–
V
+
V
+
5.7k
100k
R1
110k/10k*
V
B
–
+
2
8
A2
V
–
V
–
V
–
1789 F01
–IN
R
G
V
+
V
+
5.7k
100k
R3
110k/10k*
R2
110k/100k*
R4
110k/100k*
V
B
6
OUT
7
V
+
4
V
–
5
REF
–
+
A3
*LT1789-1/LT1789-10
APPLICATIONS INFORMATION
