LTC2415-1IGN datasheet(30/40 Pages) LINER

30 / 40 page

LTC2415/LTC2415-1

sn2415 24151fs

APPLICATIO S I FOR ATIO

Figure 25. +FS Error vs RSOURCE at REF+ or REF– (Small CIN)

Figure 26. –FS Error vs RSOURCE at REF+ or REF– (Small CIN)

Figure 27. +FS Error vs RSOURCE at REF+ and REF– (Large CREF)

Figure 28. –FS Error vs RSOURCE at REF+ and REF– (Large CREF)

RSOURCE (Ω)

100

10k

100k

2415 F25

–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

2415 F26

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

2415 F27

–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

2415 F28

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

Reference Current

In a similar fashion, the LTC2415/LTC2415-1 sample the

differential reference pins REF+ and REF– transferring

small amount of charge to and from the external driving

circuits thus producing a dynamic reference current. This

current does not change the converter offset, but it may

degrade the gain and INL performance. The effect of this

current can be analyzed in the same two distinct situa-

tions.

For relatively small values of the external reference capaci-

tors (CREF < 0.01µF), the voltage on the sampling capacitor

settles almost completely and relatively large values for

the source impedance result in only small errors. Such

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. For the LTC2415,

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 reference resistance is 1.56M

Ω which

will generate a gain error of approximately 0.32ppm for

each ohm of source resistance driving REF+ or REF–. For

the LTC2415-1, the typical differential reference resis-

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