Rainbow Electronics MAX1109 User Manual
Page 13
MAX1108/MAX1109
Single-Supply, Low-Power,
2-Channel, Serial 8-Bit ADCs
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13
Table 1. Control Byte Format
Table 2. Conversion Configuration
Table 3. Full- and Zero-Scale Voltages
*
RI = Reference Input (Table 2)
START
SEL2
SEL1
SEL0
I/ECLK
I/EREF
REFSHDN
SHDN
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
(MSB)
(LSB)
NAME
I/EREF
2
BIT
1 = internal reference, 0 = external reference. Internal reference selects +2.048V (MAX1108) or
+4.096V (MAX1109), or an external reference can be applied to the REF pin.
DESCRIPTION
I/ECLK
3
START
1 = external clock, 0 = internal clock. The SAR can be driven by the internal oscillator, or with the
SCLK signal.
SHDN
0 (LSB)
7 (MSB)
1 = operational, 0 = power down. For a full power down set REFSHDN = SHDN = 0. (See
Power-
Down Mode
section.)
The first logic “1” bit after CS goes low defines the beginning of the control byte.
SEL2
SEL1
SEL0
6
5
4
Selects the mode of operation (Table 2).
REFSHDN
1
1 = operational (if I / EREF = 1), 0 = reference shutdown. When using an external reference, power
consumption can be minimized by powering down the internal reference separately (I / EREF = 0).
REFSHDN must be set to 0 when SHDN = 0.
UNIPOLAR MODE
RI*
RI - V
REF
/ 2
Zero Scale
RI + V
REF
RI
RI + V
REF
/ 2
Negative
Full Scale
Full Scale
Zero
Scale
BIPOLAR MODE
Positive
Full Scale
SEL2
1
1
1
1
SEL1
SAMPLED INPUT
(SI)
SEL0
0
1
CH1
CH0
CONVERSION MODE
REFERENCE INPUT
(RI)
COM
COM
Unipolar
Unipolar
1
0
1
0
1
CH1
CH0
0
GND
GND
Unipolar
Unipolar
0
0
0
1
1
CH1
CH0
1
COM
COM
Bipolar
Bipolar
0
0
0
0
1
V
DD
/ 2
CH0
0
GND
CH1
Unipolar
Bipolar