MAX1401 Datasheet, PDF (22/36 Pages) Maxim Integrated Products – +3V, 18-Bit, Low-Power, Multichannel, Oversampling Sigma-Delta ADC

+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
Table 11. Channel ID Tag Codes
CID2
0
0
0
0
1
1
1
1
CID1
0
0
1
1
0
0
1
1
CID0
0
1
0
1
0
1
0
1
CHANNEL
AIN1–AIN6
AIN2–AIN6
AIN3–AIN6
AIN4–AIN6
AIN1–AIN2
AIN3–AIN4
AIN5–AIN6
Calibration
Switching Network
A switching network provides selection between three
fully differential input channels or five pseudo-differen-
tial channels, using AIN6 as a shared common. The
switching network provides two additional fully differen-
tial input channels intended for system calibration,
which may be used as extra fully differential signal
channels. Table 12 shows the channel configurations
available for both operating modes.
Scanning (SCAN Mode)
To sample and convert the available input channels
sequentially, set the SCAN control bit in the global
setup register. The sequence is determined by DIFF
(fully differential or pseudo-differential) and by the
mode control bits M1 and M0 (Tables 8, 9, and 10).
With SCAN set, the part automatically sequences
through each available channel, transmitting a single
conversion result before proceeding to the next chan-
nel. The MAX1401 automatically allows sufficient time
for each conversion to fully settle, to ensure optimum
resolution before asserting the data-ready signal and
moving to the next available channel. The scan rate,
therefore, depends on the clock bit (CLK), the filter
control bits (FS1, FS0), and the modulator frequency
selection bits (MF1, MF0).
Burn-Out Currents
The input circuitry also provides two “burn-out” cur-
rents. These small currents may be used to test the
integrity of the selected transducer. They can be selec-
tively enabled or disabled by the BOUT bit in the global
setup register.
Table 12. Input Channel Configuration in Fully Differential and Pseudo-Differential
Mode (SCAN = 0)
M1
M0
DIFF
A1
A0
MODE
HIGH INPUT
0
0
0
0
0
AIN1
0
0
0
0
1
AIN2
0
0
0
1
0
0
0
0
1
1
Pseudo-
Differential
0
0
X
X
X
AIN3
AIN4
AIN5*
0
1
X
X
X
CALOFF+**
1
0
X
X
X
CALGAIN+**
0
0
1
0
0
AIN1
0
0
1
0
1
AIN3
0
0
1
1
0
Fully
Differential
AIN5
0
1
X
X
X
CALOFF+**
1
0
X
X
X
CALGAIN+**
X = Don’t care
* This combination is available only in pseudo-differential mode when using the internal scanning logic.
** These combinations are only available in the calibration modes.
LOW INPUT
AIN6
AIN6
AIN6
AIN6
AIN6*
CALOFF-**
CALGAIN-**
AIN2
AIN4
AIN6
CALOFF-**
CALGAIN-**
22 ______________________________________________________________________________________