MAX188BEWP+T Maxim Integrated Products, MAX188BEWP+T Datasheet - Page 19

• Manufacturer Part Number: MAX188BEWP+T
• Description: IC ADC 12BIT SERIAL 20-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Data Acquisition System (DAS)r

Specifications of MAX188BEWP+T

• Resolution (bits): 12 b
• Sampling Rate (per Second): 133k
• Data Interface: Serial
• Voltage Supply Source: Dual ±
• Voltage - Supply: ±5V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 15. MAX186/MAX188 Unipolar Transfer Function,
4.096V = Full Scale
Using the buffered REFADJ input avoids external
buffering of the reference. To use the direct VREF input,
disable the internal buffer by tying REFADJ to V
Figure 15 depicts the nominal, unipolar input/output
(I/O) transfer function, and Figure 16 shows the bipolar
input/output transfer function. Code transitions occur
halfway between successive integer LSB values. Output
coding is binary with 1 LSB = 1.00mV (4.096V/4096) for
unipolar operation and 1 LSB = 1.00mV ((4.096V/2 -
-4.096V/2)/4096) for bipolar operation.
Figure 17, the MAX186 Reference-Adjust Circuit, shows
how to adjust the ADC gain in applications that use the
internal reference. The circuit provides ±1.5%
(±65LSBs) of gain adjustment range.
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 18 shows the recommended system ground
connections. A single-point analog ground (“star”
ground point) should be established at AGND, sepa-
rate from the logic ground. All other analog grounds
11 . . . 111
11 . . . 110
00 . . . 011
00 . . . 010
11 . . . 101
00 . . . 001
00 . . . 000
OUTPUT CODE
0
Transfer Function and Gain Adjust
1
Layout, Grounding, Bypassing
INPUT VOLTAGE (LSBs)
2
______________________________________________________________________________________
3
FULL-SCALE
TRANSITION
FS - 3/2LSB
1LSB = FS
FS = +4.096V
FS
DD
4096
.
and DGND should be connected to this ground. No
other digital system ground should be connected to
this single-point analog ground. The ground return to
the power supply for this ground should be low imped-
ance and as short as possible for noise-free operation.
High-frequency noise in the V
affect the high-speed comparator in the ADC. Bypass
these supplies to the single-point analog ground with
0.1µF and 4.7µF bypass capacitors close to the
MAX186/MAX188. Minimize capacitor lead lengths for
best supply-noise rejection. If the +5V power supply is
very noisy, a 10Ω resistor can be connected as a low-
pass filter, as shown in Figure 18.
Figure 16. MAX186/MAX188 Bipolar Transfer Function,
±4.096V/2 = Full Scale
Figure 17. MAX186 Reference-Adjust Circuit
Low-Power, 8-Channel,
011 . . . 111
011 . . . 110
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
100 . . . 001
100 . . . 000
100k
Serial 12-Bit ADCs
+5V
24k
-FS
1LSB = +4.096
FS = +4.096
2
4096
510k
0.01µF
INPUT VOLTAGE (LSBs)
DD
12
0V
power supply may
MAX186
REFADJ
+FS - 1LSB
19