Rainbow-electronics MAX194 Manual do Utilizador descarregar pdf (Página 14)

MAX194

REF and AIN Input Protection

The REF and AIN signals should not exceed the

MAX194 supply rails. If this can occur, diode clamp the

signal to the supply rails. Use silicon diodes and a 10Ω

current-limiting resistor (Figures 10 and 12) or Schottky

diodes without the resistor.

When using the current-limiting resistor, place the resis-

tor between the appropriate input (AIN or REF) and any

bypass capacitor. While this results in AC transients at

the input due to dynamic input currents, the transients

settle quickly and do not affect conversion results.

Improperly placing the bypass capacitor directly at the

input forms an RC lowpass filter with the current-limiting

resistor, which averages the dynamic input current and

causes linearity errors.

Analog Input

The MAX194 uses a capacitive DAC that provides an

inherent track/hold function. The input impedance is

typically 30Ω in series with 250pF in unipolar mode and

50Ω in series with 125pF in bipolar mode.

Input Range

The analog input range can be either unipolar (0V to

REF

) or bipolar (-V

REF

to V

REF

), depending on the

state of the BP/UP/SHDN pin (see

Digital Interface

sec-

tion). The reference range is 0V to VDDA. When choos-

ing the reference voltage, the equivalent MAX194 input

noise (40µV

RMS

in unipolar mode, 80µV

RMS

in bipolar

mode) should be considered.

14-Bit, 85ksps ADC with 10µA Shutdown

14 ______________________________________________________________________________________

MAX427

+15V

-15V

0.0033µF

0.1µF

ELANTEC

EL2003

+15V

-15V

0.1µF

100pF

1N914

+5V

-5V

AIN

10Ω

MAX400

+15V

-15V

1.0µF

0.1µF

1000pF

100Ω

AIN

1N914

+5V

-5V

10Ω

Figure 14. MAX400 Drives AIN for Low-Frequency Use

Figure 15. AIN Buffer for AC/DC Use

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 23 24

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