Datasheet

MAX1304–MAX1306/MAX1308–MAX1310/MAX1312–MAX1314
8-/4-/2-Channel, 12-Bit, Simultaneous-Sampling ADCs
with ±10V, ±5V, and 0 to +5V Analog Input Ranges
______________________________________________________________________________________ 27
Transfer Functions
Unipolar 0 to +5V Devices
Table 5 and Figure 12 show the offset binary transfer
function for the MAX1304/MAX1305/MAX1306 with a 0
to +5V input range. The full-scale input range (FSR) is
two times the voltage at REF. The internal +2.5V refer-
ence gives a +5V FSR, while an external +2V to +3V
reference allows an FSR of +4V to +6V, respectively.
Calculate the LSB size using:
which equals 1.22mV when using a 2.5V reference.
The input range is centered about V
MSV
, internally set
to +2.5V. For a custom midscale voltage, drive REF
MS
with an external voltage source and MSV will follow
REF
MS
. Noise present on MSV or REF
MS
directly cou-
ples into the ADC result. Use a precision, low-drift volt-
age reference with adequate bypassing to prevent MSV
from degrading ADC performance. For maximum FSR,
do not violate the absolute maximum voltage ratings of
the analog inputs when choosing MSV.
Determine the input voltage as a function of V
REF
,
V
MSV
, and the output code in decimal using:
V
CH_
= LSB x CODE
10
+ V
MSV
- 2.500V
1
2
2
12
LSB
xV
REF
=
Table 5. 0 to +5V Unipolar Code Table
BINARY
DIGITAL
OUTPUT CODE
DECIMAL
EQUIVALENT
DIGITAL OUTPUT
CODE
(CODE
10
)
INPUT VOLTAGE
(V)
V
REF
= +2.5V
V
REFMS
= +2.5V
1111 1111 1111
= 0xFFF
4095 +4.9994 ± 0.5 LSB
1111 1111 1110
= 0xFFE
4094 +4.9982 ± 0.5 LSB
1000 0000 0001
= 0x801
2049 +2.5018 ± 0.5 LSB
1000 0000 0000
= 0x800
2048 +2.5006 ± 0.5 LSB
0111 1111 1111
= 0x7FF
2047 +2.4994 ± 0.5 LSB
0000 0000 0001
= 0x001
1 +0.0018 ± 0.5 LSB
0000 0000 0000
= 0x000
0 +0.0006 ± 0.5 LSB
()
2 x V
REF
2 x V
REF
2
12
1 LSB =
BINARY OUTPUT CODE
021
3
40954093
0x0000
0x0001
0x0002
0x0003
0xFFF
0xFFE
0xFFD
0xFFC
0x7FF
0x800
0x801
2046 2048
2050
(MSV)
INPUT VOLTAGE (LSBs)
Figure 12. 0 to +5V Unipolar Transfer Function