Rainbow-electronics MAX1143 Manual de usuario descargar pdf (Pagina 14)

MAX1142/MAX1143

14-Bit ADC, 200ksps, +5V Single-Supply

with Reference

14 ______________________________________________________________________________________

External reference

An external reference can be placed at either the input

(REFADJ) or the output (REF) of the MAX1142/

MAX1143’s internal buffer amplifier.

When connecting an external reference to REFADJ, the

input impedance is typically 9kΩ. Using the buffered

REFADJ input makes buffering of the external reference

unnecessary. The internal buffer output must be

bypassed at REF with a 2.2µF capacitor.

When connecting an external reference at REF,

REFADJ must be connected to AV

. The input imped-

ance at REF is 16kΩ for DC currents. During conver-

sion, an external reference at REF must deliver 250µA

DC load current and have an output impedance of 10Ω

or less. If the reference has a higher output impedance

or is noisy, bypass it at the REF pin with a 4.7µF capac-

itor.

Analog Input

The MAX1142/MAX1143 use a capacitive DAC that

provides an inherent track/hold function. Drive AIN with

a source impedance less than 10Ω. Any signal condi-

tioning circuitry must settle with 16-bit accuracy in less

than 500ns. Limit the input bandwidth to less than half

the sampling frequency to eliminate aliasing. The

MAX1142/MAX1143 has a complex input impedance

which varies from unipolar to bipolar mode (Figure 1).

Input Range

The analog input range in unipolar mode is 0 to +12V

for the MAX1142, and 0 to +4.096V for the MAX1143. In

bipolar mode, the analog input can be -12V to +12V for

the MAX1142, and -4.096V to +4.096V for the

MAX1143. Unipolar and bipolar mode is programmed

with the UNI/BIP bit of the Control-Byte. When using a

reference other than the MAX1142/MAX1143’s internal

+4.096V reference, the full-scale input range will vary

accordingly. The full-scale input range depends on the

voltage at REF and the sampling mode selected (Tables

3 and 4).

Input Acquisition and Settling

Clocking-in a Control-Byte starts input acquisition. In

bipolar mode, the main capacitor array starts acquiring

the input as soon as a start bit is recognized. If unipolar

mode is selected by the second DIN bit, the part will

immediately switch to unipolar sampling mode and

acquire a sample.

Acquisition can be extended by eight clock cycles by

setting M1 = 1, M0 = 1 (long acquisition mode). The

sampling instant in short acquisition completes on the

falling edge of the sixth clock cycle after the start bit

(Figure 2).

+5V

510kΩ

100kΩ

24kΩ

0.22µF

REFADJ

MAX1142

Figure 7. MAX1142 Reference-Adjust Circuit

Table 3. Unipolar Full Scale and Zero Scale

PART REFERENCE ZERO SCALE FULL SCALE

Internal 0 +12V

MAX1142

External 0 +12(V

REF

/4.096)

Internal 0 +4.096V

MAX1143

External 0 +V

REF

Table 4. Bipolar Full Scale, Zero Scale, and Negative Scale

PART REFERENCE

NEGATIVE FULL

SCALE

ZERO SCALE FULL SCALE

Internal -12V 0 +12V

MAX1142

External -12(V

REF

/4.096) 0 +12(V

REF

/4.096)

Internal -4.096V 0 +4.096V

MAX1143

External -V

REF

0 +V

REF

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 20

MAX1142/MAX1143 1
SSOP.EPS 20

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Rainbow-electronics MAX1143 Manual de usuario Pagina 14

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