LTC2412IGN datasheet(27/36 Pages) LINER

27 / 36 page

LTC2412

2412f

APPLICATIO S I FOR ATIO

In addition to this gain error, the converter INL perfor-

mance is degraded by the reference source impedance.

When FO = LOW (internal oscillator and 60Hz notch), every

100

Ω of source resistance driving REF+ or REF– translates

into about 1.34ppm additional INL error. When FO = HIGH

(internal oscillator and 50Hz notch), every 100

Ω of source

resistance driving REF+ or REF– translates into about

1.1ppm additional INL error. When FO is driven by an

external oscillator with a frequency fEOSC, every 100Ω of

source resistance driving REF+ or REF– translates into

about 8.73 • 10–6 • fEOSCppm additional INL error.

Figure 22 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

Figure 18. +FS Error vs RSOURCE at REF+ or REF– (Small CIN)

Figure 19. –FS Error vs RSOURCE at REF

+ or REF– (Small CIN)

Figure 20. +FS Error vs RSOURCE at REF+ and REF– (Large CREF)

Figure 21. –FS Error vs RSOURCE at REF+ and REF– (Large CREF)

RSOURCE (Ω)

100

10k

100k

2412 F18

–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)

100

10k

100k

2412 F19

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

2412 F20

–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

2412 F21

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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