LTC2400CS8 datasheet(24/40 Pages) LINER

24 / 40 page

LTC2400

VREF = 5V). This corresponds to a 0.3ppm shift in offset

and full-scale readings for every 1

Ω of input source

resistance.

In addition to the input current spikes, the input ESD

protection diodes have a temperature dependent leakage

current. This leakage current, nominally 1nA (

±10nA

max), results in a fixed offset shift of 10

µV for a 10k source

resistance.

Reference Current (VREF)

Similar to the analog input, the reference input has a

dynamic input current. This current has negligible effect

on the offset. However, the reference current at VIN = VREF

is similar to the input current at full-scale. For large values

of reference capacitance (CVREF > 0.01µF), the full-scale

error shift is 0.3ppm/

Ω of external reference resistance

independent of the capacitance at VREF, see Figure 22. If

the capacitance tied to VREF is small (CVREF < 0.01µF), an

input resistance of up to 20k (20pF parasitic capacitance

at VREF) may be tolerated, see Figure 23.

Unlike the analog input, the integral nonlinearity of the

device can be degraded with excessive external RC time

constants tied to the reference input. If the capacitance at

node VREF is small (CVREF < 0.01µF), the reference input

can tolerate large external resistances without reduction

in INL, see Figure 24. If the external capacitance is large

(CVREF > 0.01µF), the linearity will be degraded by

0.15ppm/

Ω independent of capacitance at VREF, see

Figure 25.

APPLICATIONS INFORMATION

RESISTANCE AT VREF (Ω)

100

200

300

400

500

600

200

400

600

800

2400 F22

1000

CVREF = 10µF

CVREF = 0.01µF

CVREF = 0.1µF

VCC = 5V

VREF = 5V

VIN = 5V

TA = 25°C

CVREF = 1µF

Figure 22. Full-Scale Error vs RVREF (Large C)

RESISTANCE AT VREF(Ω)

2400 F23

100

100k

10k

–10

–20

VCC = 5V

VREF = 5V

VIN = 5V

TA = 25°C

CVREF = 100pF

CVREF = 1000pF

CVREF = 0.01µF

CVREF = 0pF

Figure 23. Full-Scale Error vs RVREF (Small C)

RESISTANCE AT VREF (Ω)

–10

100

10k

2400 F24

100k

VCC = 5V

VREF = 5V

TA = 25°C

CVREF = 0pF

CVREF = 100pF

CVREF = 1000pF

CVREF = 0.01µF

Figure 24. INL Error vs RVREF (Small C)

RSOURCE (Ω)

–300

–250

–200

–150

–100

–50

200

400

600

800

2400 F21

1000

CIN = 0.01µF

VCC = 5V

VREF = 5V

VIN = 5V

TA = 25°C

CIN = 0.1µF

CIN = 1µF

CIN = 10µF

Figure 21. Full-Scale Error vs RSOURCE (Large C)

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