MAX1323ECM-T Maxim Integrated, MAX1323ECM-T Datasheet - Page 14

• Manufacturer Part Number: MAX1323ECM-T
• Description: Analog to Digital Converters - ADC
• Manufacturer: Maxim Integrated

526ksps, Single-Channel,
14-Bit, Parallel-Interface ADCs
Connect a +2.0V to +3.0V external reference at REF
and/or REF. When connecting an external reference,
the input impedance is typically 5kΩ. The external ref-
erence must be able to drive 200µA of current and be
less than 3Ω output impedance. For more information
about using external references see the Transfer
Functions section.
For best performance use PC boards. Board layout
should ensure that digital and analog signal lines are
separated from each other. Do not run analog and digi-
tal lines parallel to one another (especially clock lines),
or do not run digital lines underneath the ADC pack-
age. Figure 5 shows the recommended system ground
connections. A single-point analog ground (star ground
point) should be established at AGND, separate from
the logic ground. All other analog grounds and DGND
should be connected to this ground. No other digital
system ground should be connected to this single-point
analog ground. The ground return to the power supply
for this ground should be low impedance and as short
as possible for noise-free operation. High-frequency
noise in the V
speed comparator in the ADC. Bypass these supplies
to the single-point analog ground with 0.1µF and 2.2µF
bypass capacitors close to the device. If the +5V
Figure 5. Power-Supply Grounding and Bypassing
14
AV
+5V
DD
______________________________________________________________________________________
OPTIONAL
FERRITE
BEAD
Layout, Grounding, and Bypassing
RETURN
AGND
DD
MAX1319
MAX1323
MAX1327
power supply may affect the high-
DV
SUPPLIES
DD
DGND
External Reference
+3V TO +5V
V
DD
CIRCUITRY
DIGITAL
RETURN
GND
MS
power supply is very noisy, a ferrite bead can be con-
nected as a lowpass filter, as shown in Figure 5.
Table 2 and Figure 6 show the two’s complement trans-
fer function for the MAX1327 with a ±10V input range.
The full-scale input range (FSR) is eight times the volt-
age at REF. The internal +2.500V reference gives a
+20V FSR, while an external +2V to +3V reference
allows an FSR of +16V to +24V, respectively. Calculate
the LSB size using the following equation:
This equals 1.2207mV with a +2.5V internal reference.
The input range is centered about V
= AGND, and the input is symmetrical at 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 ref-
erence with adequate bypassing to prevent MSV from
degrading ADC performance. For maximum full-scale
range, be careful not to violate the absolute maximum
voltage ratings of the analog inputs when choosing MSV.
Determine the input voltage as a function of V
V
ing equation:
Table 3 and Figure 7 show the two’s complement transfer
function for the MAX1323 with a ±5V input range. The
FSR is four times the voltage at REF. The internal +2.500V
reference gives a +10V FSR, while an external +2V to
+3V reference allows an FSR of +8V to +12V, respective-
ly. Calculate the LSB size using the following equation:
This equals 0.6104mV when using the internal reference.
The input range is centered about V
MSV = AGND, and the input is symmetrical at 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
full-scale range, be careful not to violate the absolute
MSV
, and the output code in decimal using the follow-
V
CH
_
1
1
LSB
LSB
=
LSB
=
=
×
8
4
CODE
×
×
V
V
2
2
Transfer Functions
REFADC
REFADC
14
14
10
Bipolar ±10V Device
Bipolar ±5V Device
MSV
+
. Normally, MSV
V
MSV
MSV
. Normally,
REF
,