9

LT1002

Test Circuit for Offset Voltage and its Drift with Temperature

–15V

+15V

*50k

*

100

Ω

*

50k

3

(10)

(11)

4

14 (7)

13 (6)

1002 TA05

*RESISTORS MUST HAVE LOW

THERMOELECTRIC POTENTIAL.

12 (5)

0.1Hz to 10Hz Noise Test Circuit

The device under test should be warmed up for three

minutes and shielded from air currents. Turn the device

180

° to measure the noise of side B.

–

+

100k

Ω

2k

Ω

100k

4.3k

110k

SCOPE

× 1

0.1

µF

4.7

µF

24.3k

10

Ω

1002 TA06

0.1

µF

22

µF

VOLTAGE GAIN = 50,000

2.2

µF

DEVICE

UNDER

TEST

A

B

(Peak to Peak noise measured in 10 Sec interval)

This circuit is also used as burn-in configuration for the

LT1002, with supply voltages increased to

±20V.

Unless proper care is exercised, thermocouple effects,

caused by temperature gradients across dissimilar metals

at the contacts to the input terminals, can exceed the

inherent drift of the amplifier. Air currents should be

minimized, package leads should be short, the two input

leads should be as close together as possible and main-

tained at the same temperature.

Channel Separation

This parameter is defined as the ratio of the change in input

offset voltage of one amplifier to the change in output

voltage of the other amplifier causing the offset change.

At low frequencies the LT1002’s channel separation is an

almost unmeasurable 148dB. As frequency increases, pin

to pin capacitance of the package, between the output of

one amplifier and the inputs of the other, becomes domi-

nant. Since these pins are non-adjacent, the capacitance is

only 0.02pF. To maintain the LT1002’s excellent channel

separation at higher frequencies, the socket and PC board

capacitances should be minimized.

Power supplies

The LT1002 is specified over a wide range of power supply

voltages from

±3V to±18V. Operation with lower supplies

is possible, down to

±1.2V (two Ni-Cad batteries). How-

ever, with

±1.2V supplies, the device is stable only in

closed loop gains of + 2 or higher (or inverting gain of one

or higher).

The V+ supply terminals are completely independent and

may be powered by separate supplies if desired (this

approach, however, would sacrifice the advantages of the

power supply rejection ratio matching). The V– supply

terminals are both connected to the common substrate

and must be tied to the same voltage. Both V – pins should

be used.