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MAX148_V5 Datasheet, PDF (19/23 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
Table 7. Full Scale and Zero Scale
UNIPOLAR MODE
Full Scale
Zero Scale
VREF + VCOM
VCOM
Positive Full Scale
VREF/2 + VCOM
BIPOLAR MODE
Zero Scale
VCOM
Negative Full Scale
- VREF/2 + VCOM
OUTPUT CODE
011 . . . 111
011 . . . 110
VFS
=
VREF
2
+ VCOM
ZS = COM
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
-VFS
=
-VREF
2
+ VCOM
1 LSB = VREF
1024
100 . . . 001
100 . . . 000
- FS
*VCOM ≥ VREF/2
COM*
INPUT VOLTAGE (LSB)
+FS - 1 LSB
+3V
R* = 10Ω
SUPPLIES
+3V GND
VDD
AGND
COM DGND
*OPTIONAL
MAX148
MAX149
+3V DGND
DIGITAL
CIRCUITRY
Figure 18. Bipolar Transfer Function, Full Scale (VFS) = VREF/2
+ VCOM, Zero Scale (ZS) = COM
deliver up to 350FA DC load current and have 10I or
less output impedance. If the reference has a higher
output impedance or is noisy, bypass it close to the VREF
pin with a 4.7FF capacitor.
Using the REFADJ input makes buffering the external
reference unnecessary. To use the direct VREF input,
disable the internal buffer by tying REFADJ to VDD.
In power-down, the input bias current to REFADJ is
typically 25FA (MAX149) with REFADJ tied to VDD. Pull
REFADJ to AGND to minimize the input bias current in
power-down.
Figure 19. Power-Supply Grounding Connection
Transfer Function
Table 7 shows the full-scale voltage ranges for unipolar
and bipolar modes.
The external reference must have a temperature coef-
ficient of 20ppm/NC or less to achieve accuracy to within
1 LSB over the 0NC to +70NC commercial temperature
range.
Figure 17 depicts the nominal, unipolar input/output
(I/O) transfer function, and Figure 18 shows the bipolar
input/output transfer function. Code transitions occur
halfway between successive-integer LSB values. Output
coding is binary, with 1 LSB = 2.44mV (2.500V/1024)
for unipolar operation, and 1 LSB = 2.44mV [(2.500V/2 -
-2.500V/2)/1024] for bipolar operation.
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