LTC2413IGN datasheet(28/44 Pages) LINER

28 / 44 page

LTC2413

sn2413 2413fs

APPLICATIO S I FOR ATIO

Figure 27 shows the typical INL error due to the source

resistance driving the REF+ or REF– pins when large CREF

values are used. The effect of the source resistance on the

two reference pins is additive with respect to this INL error.

In general, matching of source impedance for the REF+

and REF– pins does not help the gain or the INL error. The

user is thus advised to minimize the combined source

impedance driving the REF+ and REF– pins rather than to

try to match it.

The magnitude of the dynamic reference current depends

upon the size of the very stable internal sampling capaci-

tors and upon the accuracy of the converter sampling

clock. The accuracy of the internal clock over the entire

temperature and power supply range is typical better than

0.5%. Such a specification can also be easily achieved by

an external clock. When relatively stable resistors

(50ppm/

°C) are used for the external source impedance

seen by REF+ and REF–, the expected drift of the dynamic

current gain error will be insignificant (about 1% of its

value over the entire temperature and voltage range). Even

for the most stringent applications, a one-time calibration

operation may be sufficient.

In addition to the reference sampling charge, the reference

pins ESD protection diodes have a temperature dependent

leakage current. This leakage current, nominally 1nA

(

±10nA max), results in a small gain error. A 100Ω source

resistance will create a 0.05

µV typical and 0.5µV maxi-

mum full-scale error.

Figure 23. +FS Error vs RSOURCE at REF+ or REF– (Small CREF)

Figure 24. –FS Error vs RSOURCE at REF+ or REF– (Small CREF)

Figure 25. +FS Error vs RSOURCE at REF+ or REF– (Large CREF)

Figure 26. –FS Error vs RSOURCE at REF+ or REF– (Large CREF)

RSOURCE (Ω)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

2413 F23

–10

–20

–30

–40

–50

VCC = 5V

REF+ = 5V

REF – = GND

IN+ = 5V

IN – = 2.5V

FO = GND

TA = 25°C

CREF = 0.01µF

CREF = 0.001µF

CREF = 100pF

CREF = 0pF

RSOURCE (Ω)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

2413 F24

VCC = 5V

REF+ = 5V

REF – = GND

IN+ = GND

IN – = 2.5V

FO = GND

TA = 25°C

CREF = 0.01µF

CREF = 0.001µF

CREF = 100pF

CREF = 0pF

RSOURCE (Ω)

0 100 200 300 400 500 600 700 800 900 1000

2413 F25

–90

–180

–270

–360

–450

VCC = 5V

REF+ = 5V

REF– = GND

IN+ = 3.75V

IN – = 1.25V

FO = GND

TA = 25°C

CREF = 0.01µF

CREF = 0.1µF

CREF = 1µF, 10µF

RSOURCE (Ω)

0 100 200 300 400 500 600 700 800 900 1000

2413 F26

450

360

270

180

VCC = 5V

REF+ = 5V

REF– = GND

IN+ = 1.25V

IN – = 3.75V

FO = GND

TA = 25°C

CREF = 0.01µF

CREF = 0.1µF

CREF = 1µF, 10µF

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