LTC2414IGN datasheet(29/48 Pages) LINER

29 / 48 page

LTC2414/LTC2418

241418fa

values for CREF will deteriorate the converter offset and

gain performance without significant benefits of reference

filtering and the user is advised to avoid them.

Larger values of reference capacitors (CREF > 0.01µF) may

be required as reference filters in certain configurations.

Such capacitors will average the reference sampling charge

and the external source resistance will see a quasi con-

stant reference differential impedance. When FO = LOW

(internal oscillator and 60Hz notch), the typical differential

reference resistance is 1.3M

Ω which will generate a gain

error of approximately 0.38ppm for each ohm of source

resistance driving REF+ or REF–. When FO = HIGH (internal

oscillator and 50Hz notch), the typical differential refer-

ence resistance is 1.56M

Ωwhichwillgenerateagainerror

APPLICATIO S I FOR ATIO

RSOURCE (Ω)

100

10k

100k

2414/18 F18

–10

–20

–30

–40

–50

VCC = 5V

REF+ = 5V

REF – = GND

IN+ = 3.75V

IN – = 1.25V

FO = GND

TA = 25°C

CREF = 0.01µF

CREF = 0.001µF

CREF = 100pF

CREF = 0pF

RSOURCE (Ω)

100

10k

100k

2414/18 F19

VCC = 5V

REF+ = 5V

REF – = GND

IN+ = 1.25V

IN – = 3.75V

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

2414/18 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

2414/18 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

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)

of approximately 0.32ppm for each ohm of source resis-

tance driving REF+ or REF–. When FO is driven by an

external oscillator with a frequency fEOSC (external conver-

sion clock operation), the typical differential reference

resistance is 0.20 • 1012/fEOSCΩ and each ohm of source

resistance driving REF+ or REF– will result in

2.47 • 10–6 • fEOSCppm gain error. The effect of the source

resistance on the two reference pins is additive with

respect to this gain error. The typical +FS and –FS errors

for various combinations of source resistance seen by the

REF+ and REF– pins and external capacitance CREF con-

nected to these pins are shown in Figures 18, 19, 20

and 21.

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