MAX1281BCUP Maxim Integrated, MAX1281BCUP Datasheet - Page 19

• Manufacturer Part Number: MAX1281BCUP
• Description: Analog to Digital Converters - ADC
• Manufacturer: Maxim Integrated

Specifications of MAX1281BCUP

• Number Of Channels: 8/4
• Architecture: SAR
• Conversion Rate: 300 KSPs
• Resolution: 12 bit
• Input Type: Single-Ended/Pseudo-Differential
• Snr: 70 dB
• Interface Type: 4-Wire (SPI, Microwire, QSPI, TMS320)
• Operating Supply Voltage: 2.7 V to 3.6 V
• Maximum Operating Temperature: + 70 C
• Package / Case: TSSOP-20
• Maximum Power Dissipation: 559 mW
• Minimum Operating Temperature: 0 C
• Number Of Converters: 1
• Voltage Reference: 2.5 V

Figure 13. MAX1281 Reference-Adjust Circuit
Figure 14. Unipolar Transfer Function, Full Scale (FS) = V
+ V
18kΩ. During conversion, an external reference at REF
must deliver up to 350µA DC load current and have 10Ω
or less output impedance. If the reference has a higher
output impedance or is noisy, bypass it close to the REF
pin with a 4.7µF capacitor.
Using the REFADJ input makes buffering the external
reference unnecessary. To use the direct REF input,
disable the internal buffer by connecting REFADJ to
V
Table 5 shows the full-scale voltage ranges for unipolar
and bipolar modes. Figure 14 depicts the nominal,
unipolar input/output (I/O) transfer function, and Figure
15 shows the bipolar I/O transfer function. Code transi-
400ksps/300ksps, Single-Supply, Low-Power, 8-Channel,
DD1
COM
11 . . . 111
11 . . . 110
11 . . . 101
00 . . . 011
00 . . . 010
00 . . . 001
00 . . . 000
.
100kΩ
24kΩ
, Zero Scale (ZS) = V
OUTPUT CODE
+3.3V
(COM)
0
1
2
______________________________________________________________________________________
INPUT VOLTAGE (LSB)
510kΩ
3
0.01µF
COM
FULL-SCALE
TRANSITION
Serial 12-Bit ADCs with Internal Reference
Transfer Function
12
FS - 3/2LSB
REFADJ
MAX1281
1 LSB =
FS = V
ZS = V
FS
REF
COM
4096
V
REF
+ V
COM
REF
tions occur halfway between successive-integer LSB
values. Output coding is binary, with 1LSB = 610µV
for unipolar and bipolar operation.
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 16 shows the recommended system ground
connections. Establish a single-point analog ground
(star ground point) at GND. Connect all analog grounds
to the star ground. Connect the digital system ground
to star ground at this point only. For lowest-noise opera-
tion, the ground return to the star ground’s power sup-
ply should be low impedance and as short as possible.
High-frequency noise in the V
affect the high-speed comparator in the ADC. Bypass
the supply to the star ground with 0.1µF and 10µF
capacitors, located close to pin 20 of the MAX1280/
MAX1281. Minimize capacitor lead lengths for best
supply-noise rejection. If the power supply is very
noisy, a 10Ω resistor can be connected as a lowpass
filter (Figure 16).
Figure 15. Bipolar Transfer Function, Full Scale (FS) =
V
REF
*V
COM
011 . . . 111
011 . . . 110
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
100 . . . 001
100 . . . 000
/ 2 + V
≤
OUTPUT CODE
V
REF
COM
Layout, Grounding, and Bypassing
/ 2
-FS =
1 LSB =
, Zero Scale (ZS) = V
- FS
FS = V
ZS = COM
-V
REF
2
2
REF
4096
V
REF
+ V
+ V
COM
COM
INPUT VOLTAGE (LSB)
COM*
DD1
COM
power supply may
+FS - 1LSB
19