Rainbow-electronics MAX1400 User Manual download pdf (Page 33)

Grounding and Layout

For best performance, use printed circuit boards with

separate analog and digital ground planes. Wire-wrap

boards are not recommended.

Design the printed circuit board so that the analog and

digital sections are separated and confined to different

areas of the board. Join the digital and analog ground

planes at only one point. If the MAX1400 is the only

device requiring an AGND to DGND connection, then

the ground planes should be connected at the AGND

and DGND pins of the MAX1400. In systems where

multiple devices require AGND to DGND connections,

the connection should still be made at only one point.

Make the star ground as close to the MAX1400 as pos-

sible.

Avoid running digital lines under the device, because

these may couple noise onto the die. Run the analog

ground plane under the MAX1400 to minimize coupling

of digital noise. Make the power-supply lines to the

MAX1400 as wide as possible to provide low-imped-

ance paths and reduce the effects of glitches on the

power-supply line.

Shield fast switching signals, such as clocks, with digi-

tal ground to avoid radiating noise to other sections of

the board. Avoid running clock signals near the analog

inputs. Avoid crossover of digital and analog signals.

Traces on opposite sides of the board should run at

right angles to each other. This will reduce the effects

of feedthrough on the board. A microstrip technique is

best, but is not always possible with double-sided

boards. In this technique, the component side of the

board is dedicated to ground planes while signals are

placed on the solder side.

Good decoupling is important when using high-resolu-

tion ADCs. Decouple all analog supplies with 10µF tan-

talum capacitors in parallel with 0.1µF HF ceramic

capacitors to AGND. Place these components as close

to the device as possible to achieve the best decou-

pling.

See the MAX1402 evaluation kit manual for recom-

mended layout. The evaluation board package

includes a fully assembled and tested evaluation

board.

Optical Isolation

For applications that require an optically isolated

interface, refer to Figure 19. With 6N136-type optocou-

plers, maximum clock speed is 4MHz. Maximum clock

speed is limited by the degree of mismatch between

the individual optocouplers. Faster optocouplers allow

faster signaling at a higher cost.

MAX1400

+5V, 18-Bit, Low-Power, Multichannel,

Oversampling (Sigma-Delta) ADC

______________________________________________________________________________________ 33

6N136

MOSI

470Ω

SCK

MISO

INT

470Ω

INT

ISO

+5V

DOUT

SCLK

DIN

MAX1400

Figure 19. Optically Isolated Interface

Chip Information

TRANSISTOR COUNT: 34,648

SUBSTRATE CONNECTED TO AGND

1 2 ... 28 29 30 31 32 33 34 35 36

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Rainbow-electronics MAX1400 User Manual Page 33

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