Rainbow-electronics MAX194 Manual de usuario descargar pdf (Pagina 12)

MAX194

be improved by trimming, but the drift is too great to

provide good stability over temperature. The MAX427

buffer provides the necessary drive current to stabilize

the REF input quickly after capacitance changes.

The reference inaccuracies contribute additional full-

scale error. A reference with less than

⁄

total error

(61 parts per million) over the operating temperature

range is required to maintain full 14-bit accuracy. The

MAX6241 achieves a drift specification of 1ppm/°C

(typ) and easily drives the REF input directly. This

allows large temperature changes with less than 1LSB

error. While the MAX6241’s initial-accuracy specifica-

tion (0.02%) results in a maximum error of about

±4LSB, the reference voltage can be trimmed or the

offset can be corrected in software if absolute DC

accuracy is essential. Figure 11’s circuit provides out-

standing temperature stability and also provides excel-

lent DC accuracy if the initial error is corrected.

14-Bit, 85ksps ADC with 10µA Shutdown

12 ______________________________________________________________________________________

MAX194

MAX427

AGNDVSSA

VDDA

MAX874

GND

COMP

OUT

4.096V

+15V

-15V

47µF

LOW

ESR

0.1µF

1000pF

0.1µF

10Ω

REF

1N914

10Ω

-5V

+5V

4 14

2.2µF

≥ 8V

1µF

10k

2.2µF

0.1µF

MAX6241

OUT

REF

TRIM

GND

AGND

MAX194

Figure 10. Typical Reference Circuit for AC Accuracy

Figure 11. High-Accuracy Reference

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 23 24

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Rainbow-electronics MAX194 Manual de usuario Pagina 12

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