MAX1304_11 Datasheet, PDF (28/37 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
Bipolar ±5V Devices
Table 6 and Figure 13 show the two’s complement trans-
fer function for the ±5V input range MAX1308/MAX1309/
MAX1310. The FSR is four times the voltage at REF. The
internal +2.5V reference gives a +10V FSR, while an
external +2V to +3V reference allows an FSR of +8V to
+12V respectively. Calculate the LSB size using:
1 LSB
=
4
x V_REF
2¹²
which equals 2.44mV when using a 2.5V reference.
The input range is centered about V_MSV. Normally,
MSV = AGND, and the input is symmetrical about zero.
For a custom midscale voltage, drive MSV with an
external voltage source. Noise present on MSV directly
couples into the ADC result. Use a precision, low-drift
voltage reference with adequate bypassing to prevent
MSV from degrading ADC performance. For maximum
FSR, do not violate the absolute maximum voltage rat-
ings 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
Table 6. ±5V Bipolar Code Table
TWO’s
COMPLEMENT
DIGITAL OUTPUT
CODE
DECIMAL
EQUIVALENT
DIGITAL OUTPUT
CODE
(CODE₁₀)
INPUT VOLTAGE
(V)
( ) VREF = +2.5V
V_MSV = 0V
0111 1111 1111 =
0x7FF
0111 1111 1110 =
0x7FE
0000 0000 0001 =
0x001
0000 0000 0000 =
0x000
1111 1111 1111 =
0xFFF
1000 0000 0001 =
0x801
1000 0000 0000 =
0x800
+2047
+2046
+1
0
-1
-2047
-2048
+4.9988 ±0.5 LSB
+4.9963 ±0.5 LSB
+0.0037 ±0.5 LSB
+0.0012 ±0.5 LSB
-0.0012 ±0.5 LSB
-4.9963 ±0.5 LSB
-4.9988 ±0.5 LSB
0x7FF
0x7FE
0x7FD
0x7FC
0x001
0x000
0xFFF
4 x V_REF
0x803
0x802
0x801
0x800
1 LSB = ^{4 x VREF}
2¹²
-2048 -2046
-1 0 +1
+2045 +2047
(MSV)
INPUT VOLTAGE (V_{CH_} - V_MSV IN LSBs)
Figure 13. ±5V Bipolar Transfer Function
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