+2.7V to +5.25V, Low-Power, 8-Channel,

Serial 10-Bit ADCs

20

______________________________________________________________________________________

Layout, Grounding, and Bypassing

For best performance, use printed circuit boards.

Wire-wrap boards are not recommended. Board layout

should ensure that digital and analog signal lines are

separated from each other. Do not run analog and digi-

tal (especially clock) lines parallel to one another, or

digital lines underneath the ADC package.

Figure 19 shows the recommended system ground

connections. Establish a single-point analog ground

(star ground point) at AGND, separate from the logic

ground. Connect all other analog grounds and DGND

to the star ground. No other digital system ground

should be connected to this ground. For lowest-noise

operation, the ground return to the star ground’s power

supply should be low impedance and as short as

possible.

affect the high-speed comparator in the ADC. Bypass

the supply to the star ground with 0.1µF and 1µF

capacitors close to pin 20 of the MAX148/MAX149.

Minimize capacitor lead lengths for best supply-noise

rejection. If the power supply is very noisy, a 10

Ω resis-

tor can be connected as a lowpass filter (Figure 19).

20

19

18

17

16

15

14

13

12

11

1

2

3

4

5

6

7

8

9

10

MAX148

MAX149

MC683XX

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

COM

SHDN

V

DD

SCLK

CS

DIN

SSTRB

DOUT

DGND

AGND

REFADJ

VREF

(POWER SUPPLIES)

SCK

PCS0

MOSI

MISO

0.1

µF

1

µF

(GND)

0.1

µF

ANALOG

INPUTS

+3V

+3V

+2.5V

Figure 20. MAX148/MAX149 QSPI Connections, External Reference

XF

CLKX

CLKR

DX

DR

FSR

CS

SCLK

DIN

DOUT

SSTRB

TMS320LC3x

MAX148

MAX149

Figure 21. MAX148/MAX149-to-TMS320 Serial Interface