LTC1052/LTC7652
W U U
U
APPLICATIO S I FOR ATIO
When all of these errors are considered, it may seem
impossible to take advantage of the extremely low drift
specifications of the LTC1052. To show that this is not the
case, examine the temperature test circuit of Figure 3. The
lead lengths of the resistors connected to the amplifier’s
inputs are identical. The thermal capacity and thermal
resistance each input sees is balanced because of the
symmetrical connection of resistors and their identical
size. Thermal EMF-induced shifts are equal in phase and
amplitude, thus cancellation occurs.
Figure 4 shows the response of this circuit under
temperature transient conditions. Metal film resistors and
an 8-pin DIP socket were used. Care was taken in the
construction to thermally balance the inputs to the
amplifier. The units were placed in an oven and allowed to
stabilize at 25°C. The recording was started and after
100 seconds the oven, preset to 125°C, was switched on.
The test was first performed on an 8-pin plastic package
andthenwasrepeatedforaTO-5packagepluggedintothe
same test board. It is significant that the change in VOS,
even under these severe thermal transient conditions,
is quite good. As temperature stabilizes, note that the
steady-state change of VOS is well within the maximum
±0.05µV/°C drift specification.
50k
5V
2
3
7
4
–
6
100Ω
LTC1052
8
+
Very slight air currents can still affect even this
arrangement. Figure 5 shows strip charts of output noise
bothwiththecircuitcoveredandwithnocoverin“still”air.
This data illustrates why it is often prudent to enclose the
LTC1052 and its attendant components inside some form
of thermal baffle.
V
• 1000
OS
1
0.1µF
50k
0.1µF
0.1µF
–5V
LTC1052/7652 • AI04
Figure 3. Offset Drift Test Circuit
0 MIN
5 MIN
20 MIN
25 MIN
10
0
25°C TO 125°C
PLASTIC
±0.05µV/°C
10
0
25°C TO 125°C
METAL CAN
±0.05µV/°C
OVEN SWITCHED
ON (25°C)
OVEN STABILIZED
AT 12 MIN
100 SECONDS/IN
Figure 4. Transient Response of Offset Drift Test Circuit with 100°C Temperature Step
1052fa
10
Linear [ Linear ]
