LTC2402CMS datasheet(28/32 Pages) LINER

28 / 32 page

LTC2401/LTC2402

There are no extra control or status pins required to

perform the alternating 2-channel measurements. The

LTC2402 only requires two digital signals (SCK and SDO).

This simplification is ideal for isolated temperature mea-

surements or systems where minimal control signals are

available.

Pseudo Differential Applications

Generally, designers choose fully differential topologies

for several reasons. First, the interface to a 4- or 6-wire

bridge is simple (it is a differential output). Second, they

require good rejection of line frequency noise. Third, they

typically look at a small differential signal sitting on a

large common mode voltage; they need accurate

measurements of the differential signal independent of

Figure 31. Embedded Selected Channel Indicator

Figure 32. Pseudo Differential Strain Guage Application

APPLICATIO S I FOR ATIO

the common mode input voltage. Many applications

currently using fully differential analog-to-digital con-

verters for any of the above reasons may migrate to a

pseudo differential conversion using the LTC2402.

Direct Connection to a Full Bridge

The LTC2402 interfaces directly to a 4- or 6-wire bridge, as

shown in Figure 32. The LTC2402 includes a FSSET and a

ZSSET for sensing the excitation voltage directly across the

bridge. This eliminates errors due to excitation currents

flowing through parasitic resistors. The LTC2402 also

includes two single ended input channels which can tie

directly to the differential output of the bridge. The two

conversion results may be digitally subtracted yielding the

differential result.

24012 F31

SCK

SDO

CH1

• • •

CH1 DATA OUT

CH0 DATA OUT

EOC

CH0

EOC

VCC

LTC2402

FSSET

ZSSET

SCK

CH1

SDO

CH0

GND

3-WIRE

SPI INTERFACE

24012 F32

350

Ω

350

Ω

350

Ω

350

Ω

IDC = 0

IEXCITATION

IDC = 0

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