LTC1052CS datasheet(11/24 Pages) LINER

11 / 24 page

LTC1052/LTC7652

1052fa

PACKAGE-INDUCED OFFSET VOLTAGE

Since the LTC1052 is constantly fixing its own offset, it

may be asked why there is any error at all, even under

transient temperature conditions. The answer is simple.

The LTC1052 can only fix offsets inside its own nulling

loop. There are many thermal junctions outside this loop

that cannot be distinguished from legitimate signals.

Some have been discussed previously, but the package

thermal EMF effects are an important source of errors.

Notice the difference in the thermal response curves of

Figure 4. This can only be attributed to the package since

everything else is identical. In fact, the VOS specification is

set by the package-induced warm-up drift, not by the

LTC1052. TO-99 metal cans exhibit the worst warm-up

drift and Linear Technology sample tests TO-99 lots to

minimize this problem.

Two things make 100% screening costly: (1) The extreme

precision required on the LTC1052 and (2) the thermal

time constant of the package is 0.5 to 3 minutes, depend-

ing on package type. The first precludes the use of auto-

matic handling equipment and the second takes a long

time. Bench test equipment is available to 100% test for

warmed-up drift if offsets of less than ±5µV are required.

APPLICATIO S I FOR ATIO

Figure 5. DC to 1Hz (Test Circuit TC3)

1µV

#1 COVERED

#1 UNCOVERED

#2 UNCOVERED

20 SEC

CLOCK

The LTC1052 has an internal clock, setting the nominal

sampling frequency at 330Hz. On 8-pin devices, there is

no way to control the clock externally. In some applica-

tions it may be desirable to control the sampling clock and

this is the function of the 14-pin device.

CLK IN, CLK OUT and INT/EXT are provided to accomplish

this. With no external connection, an internal pull-up holds

INT/EXT at the V+ supply and the 14-pin device self-

oscillates at 330Hz. In this mode there is a signal on the

CLK IN pin of 660Hz (2 times sampling frequency) with a

30% duty cycle. A divide-by-two drives the CLK OUT pin

and sets the sampling frequency.

To use an external clock, connect INT/EXT to V– and the

external clock to CLK IN. The logic threshold of CLK IN is

2.5V below the positive supply; this allows CMOS logic to

drive it directly with logic supplies of V+ and ground. CLK

IN can be driven from V+ to V– if desired. The duty cycle of

the external clock is not particularly critical but should be

kept between 30% and 60%.

Capacitance between CLK IN and CLK OUT (pins 13 and

12) can cause the divide-by-two circuit to malfunction. To

avoid this, keep this capacitance below 5pF.

LTC1052CS датащи(PDF) 11 Page - Linear Technology

LTC1052CS датащи(HTML) 11 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

датащи скачать

ссылки URL