MAX127ACAI Просмотр технического описания (PDF) - Maxim Integrated

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MAX127ACAI

Multirange, +5V, 12-Bit DAS with 2-Wire Serial Interface

Maxim Integrated 

Multirange, +5V, 12-Bit DAS with

2-Wire Serial Interface

Transfer Function

Output data coding for the MAX127/MAX128 is binary

in unipolar mode with 1LSB = (FS/4096) and

two’s complement binary in bipolar mode with 1LSB =

[(2 x | FS |) / 4096]. Code transitions occur halfway

between successive-integer LSB values. Figures 13a

and 13b show the input/output (I/O) transfer functions

for unipolar and bipolar operations, respectively. For

full-scale (FS) values, refer to Table 3.

OUTPUT CODE

11... 111

11... 110

11... 101

FULL-SCALE

TRANSITION

1 LSB =

FS

4096

Layout, Grounding, and Bypassing

Careful printed circuit board layout is essential for best

system performance. For best performance, use a

ground plane. To reduce crosstalk and noise injection,

keep analog and digital signals separate. Connect ana-

log grounds and DGND in a star configuration to

AGND. For noise-free operation, ensure the ground

return from AGND to the supply ground is low imped-

ance and as short as possible. Connect the logic

grounds directly to the supply ground. Bypass VDD with

0.1µF and 4.7µF capacitors to AGND to minimize high-

and low-frequency fluctuations. If the supply is exces-

sively noisy, connect a 5Ω resistor between the supply

and VDD, as shown in Figure 14.

00... 011

00... 010

00... 001

00... 000

01 2 3

INPUT VOLTAGE (LSB)

FS

FS - 3/2 LSB

Figure 13a. Unipolar Transfer Function

OUTPUT CODE

011... 111

011... 110

1 LSB =

2FS

4096

SUPPLY

+5V

GND

R* = 5Ω

4.7µF

0.1µF

**

VDD

AGND

MAX127

MAX128

DGND

+5V DGND

DIGITAL

CIRCUITRY

* OPTIONAL

** CONNECT AGND AND DGND WITH A GROUND PLANE OR A SHORT TRACE.

Figure 14. Power-Supply Grounding Connection

000... 001

000... 000

111... 111

100... 010

100... 001

100... 000

-FS

0

INPUT VOLTAGE (LSB)

Figure 13b. Bipolar Transfer Function

+FS - 1 LSB

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