MAX1304_11 Datasheet, PDF (27/37 Pages) Maxim Integrated Products – 8-/4-/2-Channel, 12-Bit, Simultaneous-Sampling ADCs with ±10V, ±5V

8-/4-/2-Channel, 12-Bit, Simultaneous-Sampling ADCs
with ±10V, ±5V, and 0 to +5V Analog Input Ranges
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:
1 LSB
=
2
x V_REF
2¹²
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 CODE₁₀ + V_MSV - 2.500V
Table 5. 0 to +5V Unipolar Code Table
BINARY
DIGITAL
OUTPUT CODE
DECIMAL
EQUIVALENT
DIGITAL OUTPUT
CODE
(CODE₁₀)
INPUT VOLTAGE
(V)
( ) VREF = +2.5V
V_REFMS = +2.5V
1111 1111 1111
= 0xFFF
1111 1111 1110
= 0xFFE
1000 0000 0001
= 0x801
1000 0000 0000
= 0x800
0111 1111 1111
= 0x7FF
0000 0000 0001
= 0x001
0000 0000 0000
= 0x000
4095
4094
2049
2048
2047
1
0
+4.9994 ± 0.5 LSB
+4.9982 ± 0.5 LSB
+2.5018 ± 0.5 LSB
+2.5006 ± 0.5 LSB
+2.4994 ± 0.5 LSB
+0.0018 ± 0.5 LSB
+0.0006 ± 0.5 LSB
0xFFF
0xFFE
0xFFD
0xFFC
0x801
0x800
0x7FF
2 x V_REF
0x0003
0x0002
0x0001
0x0000
0 123
1 LSB = ^{2 x VREF}
2¹²
2046 2048 2050
(MSV)
INPUT VOLTAGE (LSBs)
4093 4095
Figure 12. 0 to +5V Unipolar Transfer Function
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