參數(shù)資料
型號: MAX148-MAX149
廠商: Maxim Integrated Products, Inc.
英文描述: +2.7V to +5.25V, Low-Power, 8-Channel, Serial 10-Bit ADCs
中文描述: 2.7V至5.25V,低功耗,8通道,串行10位ADC
文件頁數(shù): 19/24頁
文件大?。?/td> 221K
代理商: MAX148-MAX149
M
+2.7V to +5.25V, Low-Power, 8-Channel,
S erial 10-Bit ADCs
______________________________________________________________________________________
19
VREF, the DC input resistance is a minimum of 18k
.
During conversion, an external reference at VREF must
deliver up to 350μA DC load current and have 10
or
less output impedance. If the reference has a higher
output impedance or is noisy, bypass it close to the
VREF pin with a 4.7μF 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 V
DD
. In
power-down, the input bias current to REFADJ is typi-
cally 25μA (MAX149) with REFADJ tied to V
DD
. Pull
REFADJ to AGND to minimize the input bias current in
power-down.
T ransfer Func tion
Table 7 shows the full-scale voltage ranges for unipolar
and bipolar modes.
The external reference must have a temperature coeffi-
cient of 20ppm/°C or less to achieve accuracy to within
1LSB over the 0°C to +70°C 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 1LSB = 2.44mV (2.500V /
1024) for unipolar operation, and 1LSB = 2.44mV
[(2.500V / 2 - -2.500V / 2) / 1024] for bipolar operation.
011
. . .
111
011
. . .
110
000
. . .
010
000
. . .
001
000
. . .
000
111
. . .
111
111
. . .
110
111
. . .
101
100
. . .
001
100
. . .
000
- FS
COM*
INPUT VOLTAGE (LSB)
OUTPUT CODE
ZS = COM
+FS - 1LSB
*COM VREF / 2
+ COM
FS
= V2
-FS =
+ COM
-VREF
2
1LSB = 1024
Figure 18. Bipolar Transfer Function, Full Scale (FS) =
VREF / 2 + COM, Zero Scale (ZS) = COM
+3V
+3V
GND
SUPPLIES
DGND
+3V
DGND
COM
AGND
V
DD
DIGITAL
CIRCUITRY
MAX148
MAX149
R* = 10
*OPTIONAL
Figure 19. Power-Supply Grounding Connection
UNIPOLAR MODE
BIPOLAR MODE
Full Scale
Zero Scale
Positive
Full Scale
Zero
Scale
Negative
Full Scale
VREF + COM
COM
VREF / 2
+ COM
COM
-VREF / 2
+ COM
Table 7. Full Scale and Zero Scale
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