Rainbow Electronics MAX1189 - Manual (Page 10)

MAX1179/MAX1187/MAX1189
Shutdown Mode
In shutdown mode, the reference and reference buffer
shut down between conversions. Shutdown mode
reduces supply current to 0.5µA (typ) immediately after
the conversion. The next falling edge of CS with R/C
low causes the reference and buffer to wake up and
enter acquisition mode. To achieve 16-bit accuracy,
allow 12ms (C
REFADJ = 0.1µF, C REF = 10µF) for the
internal reference to wake up.
Internal and External Reference
Internal Reference
The internal reference of the MAX1179/MAX1187/
MAX1189 is internally buffered to provide +4.096V out-
put at REF. Bypass REF to AGND and REFADJ to
AGND with 10µF and 0.1µF, respectively.
Sink or source current at REFADJ to make fine adjust-
ments to the internal reference. The input impedance of
REFADJ is nominally 5k
Ω. Use the circuit of Figure 7 to
adjust the internal reference to ±1.5%.
External Reference
An external reference can be placed at either the input
(REFADJ) or the output (REF) of the MAX1179/
MAX1187/MAX1189’s internal buffer amplifier. Using
the buffered REFADJ input makes buffering the external
reference unnecessary. The input impedance of
REFADJ is typically 5k
Ω. The internal buffer output
must be bypassed at REF with a 10µF capacitor.
Connect REFADJ to AV
DD
to disable the internal buffer.
Directly drive REF using an external 3.8V to 4.2V refer-
ence. During conversion, the external reference must
be able to drive 100µA of DC load current and have an
output impedance of 10
Ω or less.
For optimal performance, buffer the reference through
an op amp and bypass REF with a 10µF capacitor.
Consider the MAX1179/MAX1187/MAX1189’s equivalent
input noise (0.6LSB) when choosing a reference.
Reading the Conversion Result
EOC flags the microprocessor when a conversion 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 MAX1179/MAX1187/
MAX1189. 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
MAX1179/MAX1187/MAX1189 then wait for the next
falling edge of CS to start the next conversion cycle
(see Figure 2).
16-Bit, 135ksps, Single-Supply ADCs with
Bipolar Analog Input Range
10 ______________________________________________________________________________________
Figure 6. Selecting Shutdown Mode
CS
EOC
REF &
BUFFER
POWER
ACQUISITION CONVERSION
DATA
OUT
R/C
Figure 7. MAX1179/MAX1187/MAX1189 Reference Adjust
Circuit
MAX1179
MAX1187
MAX1189
REFADJ
+5V
68k Ω
100k Ω
150k Ω
0.1 µF