MAX148 Datasheet, PDF (20/24 Pages) Maxim Integrated Products – +2.7V to +5.25V, Low-Power, 8-Channel, Serial 10-Bit ADCs

+2.7V to +5.25V, Low-Power, 8-Channel,
Serial 10-Bit ADCs
ANALOG
INPUTS
1 _CH0
2 _CH1
V_DD ²⁰
SCLK ¹⁹
3 CH2
CS 18
4 CH3 _{MAX148 DIN} 17
MAX149
5 CH4
SSTRB 16
6 CH5
DOUT 15
7 CH6
DGND 14
8 CH7
AGND 13
9 COM
REFADJ 12
10 SHDN
VREF 11
0.1µF
0.1µF
+2.5V
+3V +3V
1µF
(POWER SUPPLIES)
SCK
PCS0
MOSI
MC683XX
MISO
(GND)
Figure 20. MAX148/MAX149 QSPI Connections, External Reference
XF
CLKX
TMS320LC3x
CLKR
DX
DR
FSR
CS
SCLK
MAX148
MAX149
DIN
DOUT
SSTRB
Figure 21. MAX148/MAX149-to-TMS320 Serial Interface
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.
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 0.1µF 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 10Ω resis-
tor can be connected as a lowpass filter (Figure 19).
20 ______________________________________________________________________________________