LTC1052/LTC7652

10

1052fa

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

and then was repeated for a TO-5 package plugged into the

even under these severe thermal transient conditions,

is quite good. As temperature stabilizes, note that the

±0.05µV/°C drift specification.

Very slight air currents can still affect even this

arrangement. Figure 5 shows strip charts of output noise

both with the circuit covered and with no cover in “still” air.

This data illustrates why it is often prudent to enclose the

LTC1052 and its attendant components inside some form

of thermal baffle.

Figure 3. Offset Drift Test Circuit

Figure 4. Transient Response of Offset Drift Test Circuit with 100°C Temperature Step

0 MIN

25 MIN

20 MIN

5 MIN

10

0

0

10

OVEN SWITCHED

ON (25°C)

OVEN STABILIZED

AT 12 MIN

100 SECONDS/IN

25°C TO 125°C

PLASTIC

25°C TO 125°C

METAL CAN

±0.05µV/°C

±0.05µV/°C

0.1µF

0.1µF

50k

3

2

7

6

8

4

1

5V

LTC1052/7652 • AI04

100Ω

50k

–5V

0.1µF

–

LTC1052

+