Rainbow Electronics MAX1033 - Manual (Page 25)

This prevents the MAX1032/MAX1033 from inadvertent-
ly exiting full power-down mode because of a CS glitch
in a noisy digital environment.
Power-On Reset
The MAX1032/MAX1033 power up in normal operation
configured for external clock mode with all circuitry
active (Tables 7 and 8). Each analog input channel
(CH0–CH7) is set for single-ended conversions with a
±12V bipolar input range (Table 6).
Allow the power supplies to stabilize after power-up. Do
not initiate any conversions until the power supplies
have stabilized. Additionally, allow 10ms for the internal
reference to stabilize when C
REF = 1.0µF and C RECAP
= 0.1µF. Larger reference capacitors require longer
stabilization times.
Internal or External Reference
The MAX1032/MAX1033 operate with either an internal or
external reference. The reference voltage impacts the
ADC’s FSR (Figures 12, 13, and 14). An external refer-
ence is recommended if more accuracy is required than
the internal reference provides, and/or multiple converters
require the same reference voltage.
Internal Reference
The MAX1032/MAX1033 contain an internal 4.096V
bandgap reference. This bandgap reference is connect-
ed to REFCAP through a nominal 5k
Ω resistor (Figure 17).
The voltage at REFCAP is buffered creating 4.096V at
REF. When using the internal reference, bypass
REFCAP with a 0.1µF or greater capacitor to AGND1 and
bypass REF with a 1.0µF or greater capacitor to AGND1.
External Reference
For external reference operation, disable the internal
reference and reference buffer by connecting REFCAP
to AV
DD1
. With AV
DD1
connected to REFCAP, REF
becomes a high-impedance input and accepts an
external reference voltage. The MAX1032/MAX1033
external reference current varies depending on the
applied reference voltage and the operating mode (see
the External Reference Input Current vs. External
Reference Input Voltage in the Typical Operating
Characteristics).
Applications Information
Noise Reduction
Additional samples can be taken and averaged (over-
sampling) to remove the effect of transition noise on
conversion results. The square root of the number of
samples determines the improvement in performance.
For example, with 2/3LSB
RMS (4LSB P-P ) transition
noise, 16 (4 2 = 16) samples must be taken to reduce
the noise to 1LSB P-P .
Interface with 0 to 10V Signals
In industrial-control applications, 0 to 10V signaling is
common. For 0 to 10V applications, configure the select-
ed MAX1032/MAX1033 input channel for the single-
ended 0 to 12V input range (R[2:0] = 110, Table 6). The 0
to 12V range accommodates 0 to 10V where the signals
saturate at approximately 12V if out of range.
Interface with 4–20mA Signals
Figure 19 illustrates a simple interface between the
MAX1032/MAX1033 and a 4–20mA signal. 4–20mA sig-
naling can be used as a binary switch (4mA represents
a logic-low signal, 20mA represents a logic-high sig-
nal), or for precision communication where currents
between 4mA and 20mA represent intermediate analog
data. For binary switch applications, connect the
4–20mA signal to the MAX1032/MAX1033 with a resis-
tor to ground. For example, a 250
Ω resistor converts
the 4–20mA signal to a 1V to 5V signal. Adjust the
resistor value so the parallel combination of the resistor
and the MAX1032/MAX1033 source impedance is
250
Ω. In this application, select the single-ended 0 to
6V range (R[2:0] = 011, Table 6). For applications that
require precision measurements of continuous analog
currents between 4mA and 20mA, use a buffer to pre-
vent the MAX1032/MAX1033 input from diverting cur-
rent from the 4–20mA signal.
MAX1032/MAX1033
8-/4-Channel, ±12V Multirange Inputs,
Serial 14-Bit ADCs
______________________________________________________________________________________ 25
REF
REFCAP
AGND1
4.096V
BANDGAP
REFERENCE
5k Ω
1x
SAR
ADC REF
4.096V
1.0 µF
0.1 µF
V RCTH
MAX1032
MAX1033
Figure 17. Internal Reference Operation