MAX1201 Datasheet, PDF (9/16 Pages) Maxim Integrated Products – +5v sINGLE-sUPPLY, 2.2mSPS, 14-bIT sELF-cALIBRATING adc

+5V Single-Supply, 2.2Msps, 14-Bit
Self-Calibrating ADC
CM
RFPS
RFPF
RFPF
INP
RFNF
INN
RFNF
RFPF
RFNS
CM
Figure 2. Simplified MDAC Architecture
Choice of Reference
It is important to choose a low-noise reference, such as
the MAX6341, which can provide both excellent load
regulation and low temperature drift. The equivalent
input circuit for the reference pins is shown in Figure 3.
Note that the reference pins drive approximately 1kΩ of
resistance on chip. They also drive a switched capacitor
of 21pF. To meet the dynamic performance, the refer-
ence voltage is required to settle to 0.0015% within one
clock cycle. Carefully choose an appropriate driving cir-
cuit (Figure 4). The capacitors at the reference pins
(RFPF, RFNF) provide the dynamic charge required dur-
ing each clock cycle, while the op amps ensure accura-
cy of the reference signals. These capacitors must have
low dielectric-absorption characteristics, such as poly-
styrene or teflon capacitors.
The reference pins can be connected to either single-
ended or differential voltages within the specified maxi-
mum levels. Typically, the positive reference pin (RFPF)
would be driven to 4.096V, and the negative reference
pin (RFNF) connected to analog ground. There are
sense pins, RFPS and RFNS, which can be used with
external amplifiers to compensate for any resistive drop
on these lines, internal or external to the chip. Assure a
correct reference voltage by using proper Kelvin con-
nections at the sense pins.
Common-Mode Voltage
The switched capacitor circuit at the analog input allows
signals between AGND and the analog power supply.
Since the common-mode voltage has a strong influence
on the performance of the ADC, the best results are
obtained by choosing V_CM to be at half the difference
between the reference voltages V_RFP and V_RFN. Achieve
Figure 3. Equivalent Input at the Reference Pins. The sense
pins should not draw any DC current.
V_RFP = 4.096V
5k
MAX410
5k
V_RFN = 0V
MAX410
MAX410
CHIP BOUNDARY
RFPF
RFPS
RFNF
RFNS
CM
Figure 4. Drive Circuit for Reference Pins and Common-Mode
Pin
this by using a resistive divider between the two refer-
ence potentials. Figure 4 shows the driving circuit for
good dynamic performance.
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