LTC2400CS8 datasheet(28/40 Pages) LINER

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LTC2400

TYPICAL APPLICATIONS

0.1

µF

VIN

SDO

SCK

CHIP SELECT

SERIAL

VREF

VREFIN

VCC

0.1

µF

GND

LTC2400

µF

EXT

µF

LARGE

MAGNITUDE

DIFFERENTIAL

INPUT

0.01

µF

0.1

µF

2400 F29

–5V

1/2

LTC1043

Figure 29. Simple Rail-to-Rail Circuit Converts Differential Signals to Single-Ended Signals

LTC2400 High Accuracy Differential to Single-Ended

Converter for

±5V Supplies

The circuit in Figure 30 is ideal for low level differential

signals in applications that have a

±5V supply and need

high accuracy without calibration. The circuit combines an

LTC1043 and LTC1050 as a differential to single-ended

amplifier that has an input common mode range that

includes the power supplies. Resistors R1 and R2 set the

LTC1050’s gain at 101.

The circuit schematic shows an optional resistor RS. This

resistor can be placed in series with the LTC2400’s input

to limit current if the input goes below – 300mV. The

resistor does not degrade the converter’s performance as

long as any capacitance, stray or otherwise, connected

between the LTC2400’s input and ground is less than

100pF. Higher capacitance will increase offset and full-

scale errors (see Input Current section).

The circuit achieves a nonlinearity of

±1ppm, input re-

ferred noise of 0.05

µVRMS (averaging 64 samples), 19.6

bits resolution for a full-scale input of 40mV, and an overall

accuracy of 20 bits when using an LTC1236-5 precision

5V reference.

Multiple Inputs

The simple circuit shown in Figure 31 takes advantage of

the LTC2400’s single conversion settling. The LTC1391

serially programmed multiplexer allows accurate conver-

sions on each of its eight channels without introducing any

offset, gain or linearity errors with its input signal between

0V and VREF, as long as the total capacitance connected to

the LTC2400’s input is less than 1000pF. A small 2ppm

(typ) error occurs when an active input channel’s signal

voltage reaches –300mV (typ). If the excursion below

ground is above – 200mV (typ), the error is less than the

LTC2400’s 0.3ppmRMS noise. On the topside, the selected

input signal’s magnitude can go above the 5V supply with

no linearity degradation or increased noise. Figure 31’s

circuit can tolerate overdrive on the unselected channel

without conversion degradation as long as the overdrive is

less than 250mV above the supply voltage or 250mV

below ground. The linearity performance is similar to that

shown in the Typical Performance Characteristics section.

Errors caused by channel-to-channel crosstalk are less

than the LTC2400’s typical input noise. This remains the

case for a frequency range of 1Hz to 153.6kHz (the

LTC2400’s internal clock frequency or 10fS). When the

frequency reaches 1.536MHz (4VP-P), the RMS noise typi-

cally doubles and the linearity is degraded by 30ppm (typ).

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