LTC2413IGN datasheet(36/44 Pages) LINER

36 / 44 page

LTC2413

sn2413 2413fs

APPLICATIO S I FOR ATIO

Figure 43. Simple Bridge Connection

REF+

REF–

SDO

SCK

IN+

IN–

GND

VREF

350

Ω

BRIDGE

2413 F43

1, 7, 8, 9,

10, 15, 16

LTC2413

R1 AND R2 CAN BE USED TO INCREASE TOLERABLE AC COMPONENT ON REF SIGNALS

LT1019

For those applications that cannot be fulfilled by the

LTC2413 alone, compensating for error in external ampli-

fication can be done effectively due to the “no latency”

feature of the LTC2413. No latency operation allows

samples of the amplifier offset and gain to be interleaved

with weighing measurements. The use of correlated double

sampling allows suppression of 1/f noise, offset and

thermocouple effects within the bridge. Correlated double

sampling involves alternating the polarity of excitation and

dealing with the reversal of input polarity mathematically.

Alternatively, bridge excitation can be increased to as

much as

±10V, if one of several precision attenuation

techniques is used to produce a precision divide operation

on the reference signal. Another option is the use of a

reference within the 5V input range of the LTC2413 and

developing excitation via fixed gain, or LTC1043 based

voltage multiplication, along with remote feedback in the

excitation amplifiers, as shown in Figures 48 and 50.

Figure 43 shows an example of a simple bridge connec-

tion. Note that it is suitable for any bridge application

where measurement speed is not of the utmost impor-

tance. For many applications where large vessels are

weighed, the average weight over an extended period of

time is of concern and short term weight is not readily

determined due to movement of contents, or mechanical

resonance. Often, large weighing applications involve load

cells located at each load bearing point, the output of

which can be summed passively prior to the signal pro-

cessing circuitry, actively with amplification prior to the

ADC, or can be digitized via multiple ADC channels and

summed mathematically. The mathematical summation

of the output of multiple LTC2413’s provides the benefit of

a root square reduction in noise. The low power consump-

tion of the LTC2413 makes it attractive for multidrop

communication schemes where the ADC is located within

the load-cell housing.

A direct connection to a load cell is perhaps best incorpo-

rated into the load-cell body, as minimizing the distance to

the sensor largely eliminates the need for protection

devices, RFI suppression and wiring. The LTC2413 exhib-

its extremely low temperature dependent drift. As a result,

exposure to external ambient temperature ranges does

not compromise performance. The incorporation of any

amplification considerably complicates thermal stability,

as input offset voltages and currents, temperature coeffi-

cient of gain settling resistors all become factors.

The circuit in Figure 44 shows an example of a simple

amplification scheme. This example produces a differen-

tial output with a common mode voltage of 2.5V, as

determined by the bridge. The use of a true three amplifier

instrumentation amplifier is not necessary, as the LTC2413

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