MAX1165-MAX1166 Datasheet, PDF (11/15 Pages) Maxim Integrated Products – Low-Power, 16-Bit Analog-to-Digital Converters with Parallel Interface

Low-Power, 16-Bit Analog-to-Digital Converter
with Parallel Interface
external reference to REFADJ, the input impedance is
typically 5kΩ. Using the buffered REFADJ input makes
buffering the external reference unnecessary; however,
the internal buffer output must be bypassed at REF with
a 1µF capacitor.
Connect REFADJ to AV_DD to disable the internal buffer.
Directly drive REF using an external reference. During
conversion the external reference must be able to drive
100µA of DC load current and have an output imped-
ance of 10Ω or less. REFADJ’s impedance is typically
5kΩ. The DC input impedance of REF is a minimum
40kΩ.
For optimal performance, buffer the reference through
an op amp and bypass REF with a 1µF capacitor.
Consider the MAX1165/MAX1166s’ equivalent input
noise (38µV_RMS) when choosing a reference.
Reading a Conversion Result
EOC is provided to flag the microprocessor when a con-
version is complete. The falling edge of EOC signals
that the data is valid and ready to be output to the bus.
D0–D15 are the parallel outputs of the MAX1165/
MAX1166. These three-state outputs allow for direct
connection to a microcontroller I/O bus. The outputs
remain high-impedance during acquisition and conver-
sion. Data is loaded onto the bus with the third falling
edge of CS with R/C high after t_DO. Bringing CS high
forces the output bus back to high impedance. The
MAX1165/MAX1166 then wait for the next falling edge
of CS to start the next conversion cycle (Figure 2).
The MAX1165 loads the conversion result onto a 16-bit
wide data bus while the MAX1166 has a byte-wide out-
put format. HBEN toggles the output between the
most/least significant byte. The least significant byte is
loaded onto the output bus when HBEN is low and the
most significant byte is on the bus when HBEN is high
(Figure 2).
RESET
Toggle RESET with CS high. The next falling edge of CS
begins acquisition. This reset is an alternative to the
dummy conversion explained in the Starting a Conversion
section.
Transfer Function
Figure 8 shows the MAX1165/MAX1166 output transfer
function. The output is coded in standard binary.
Input Buffer
Most applications require an input buffer amplifier to
achieve 16-bit accuracy. If the input signal is multi-
OUTPUT CODE
11...111
11...110
11...101
FULL-SCALE
TRANSITION
FS = V_REF
00...011
00...010
00...001
00...000
012 3
INPUT VOLTAGE (LSB) FS - 3/2LSB
1LSB = V_REF
65536
FS
Figure 8. MAX1165/MAX1166 Transfer Function
plexed, the input channel should be switched immedi-
ately after acquisition, rather than near the end of or
after a conversion. This allows more time for the input
buffer amplifier to respond to a large step change in
input signal. The input amplifier must have a high
enough slew rate to complete the required output volt-
age change before the beginning of the acquisition
time. At the beginning of acquisition, the internal sam-
pling capacitor array connects to AIN (the amplifier out-
put), causing some output disturbance. Ensure that the
sampled voltage has settled to within the required limits
before the end of the acquisition time. If the frequency
of interest is low, AIN can be bypassed with a large
enough capacitor to charge the internal sampling
capacitor with very little ripple. However, for AC use,
AIN must be driven by a wideband buffer (at least
10MHz), which must be stable with the ADC’s capaci-
tive load (in parallel with any AIN bypass capacitor
used) and also settle quickly. An example of this circuit
using the MAX4434 is given in Figure 9.
ANALOG
INPUT
10Ω
MAX4434
MAX1165
MAX1166
AIN
40pF
Figure 9. MAX1165/MAX1166 Fast Settling Input Buffer
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