Datasheet

+2.7V to +5.25V, Low-Power, 8-Channel,
Serial 10-Bit ADCs
MAX148/MAX149
20
Layout, Grounding, and Bypassing
For best performance, use PCBs. 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 digital (especially clock)
lines parallel to one another, or digital lines underneath
the ADC package.
Figure 19 shows the recommended system ground con-
nections. 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 con-
nected 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.
High-frequency noise in the V
DD
power supply may
affect the high-speed comparator in the ADC. Bypass
the supply to the star ground with 0.1FF and 1FF capaci-
tors 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 10I resistor can be
connected as a lowpass filter (Figure 19).
Figure 20. MAX148/MAX149 QSPI Connections, External Reference
Figure 21. MAX148/MAX149-to-TMS320 Serial Interface
20
19
18
17
16
15
14
13
12
11
1
2
3
4
5
6
7
8
9
10
MC683XX
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
COM
V
DD
SCLK
DIN
SSTRB
DOUT
DGND
AGND
REFADJ
V
REF
(POWER SUPPLIES)
SCK
PCS0
MOSI
MISO
0.1µF
1µF
(GND)
0.1µF
ANALOG
INPUTS
+3V
+3V
+2.5V
MAX148
MAX149
SHDN
CS
+
XF
CLKX
CLKR
DX
DR
FSR
SCLK
DIN
DOUT
SSTRB
TMS320LC3x
CS
MAX148
MAX149