Rainbow Electronics MAX1401 User Manual
Page 17
MAX1401
+3V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC
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17
channels, selection of either calibration mode (01 or 10)
will cause the scanning sequence to be extended to
include a conversion on both the CALGAIN+/CALGAIN-
input pair and the CALOFF+/CALOFF- input pair. The
exact sequence depends on the state of the DIFF bit
(Table 4). When scanning, the calibration channels use
the PGA gain, format, and DAC settings defined by the
contents of Transfer Function Register 3.
BUFF:
(Default = 0) The BUFF bit controls operation of
the input buffer amplifiers. When this bit is 0, the inter-
nal buffers are bypassed and powered down. When
this bit is set high, the buffers drive the input sampling
capacitors and minimize the dynamic input load.
DIFF:
(Default = 0) Differential/Pseudo-Differential Bit.
When DIFF = 0, the part is in pseudo-differential mode,
and AIN1–AIN5 are measured respective to AIN6, the
analog common. When DIFF = 1, the part is in differen-
tial mode with the analog inputs defined as AIN1/AIN2,
AIN3/AIN4, and AIN5/AIN6. The available input chan-
nels for each mode are tabulated in Table 5. Note that
DIFF also affects the scanning sequence when the part
is placed in SCAN mode (Table 4).
BOUT:
(Default = 0) Burn-out Current Bit. Setting BOUT
= 1 connects 100nA current sources to the selected
analog input channel. This mode is used to check that a
transducer has not burned out or opened circuit. The
burn-out current source must be turned off (BOUT = 0)
before measurement to ensure best linearity.
RESERVED:
(Default = 0) Reserved Bit. A 0 must be
written to this location.
X2CLK:
(Default = 0) Times-Two Clock Bit. Setting this
bit to 1 selects a divide-by-2 prescaler in the clock sig-
nal path. This allows use of a higher frequency crystal
or clock source and improves immunity to asymmetric
clock sources.
Table 2. Data Output Rate vs. CLK, Filter Select, and Modulator Frequency Bits
*
Data rates offering noise-free 16-bit resolution.
Note:
When FAST = 0, f
-3dB
= 0.262
·
Data Rate. When FAST = 1, f
-3dB
= 0.443
·
Data Rate.
Note:
Default condition is in bold print.
Table 3. Special Modes Controlled by M1, M0 (SCAN = 0)
1
0
1
0
1
0
1
0
MF0
1
1
0
0
1
1
0
0
MF1
1
1
1
1
0
0
0
0
CLK
2400
4800
400
480
4.9152
2.4576
1200
2400
200
240
4.9152
2.4576
600
1200
100
120
4.9152
2.4576
300
600
50
60
4.9152
2.4576
800
1600
160
200
2.048
1.024
400
800
80
100
2.048
1.024
200
400
40
50
2.048
1.024
FS1, FS0
(1, 0)
FS1, FS0
(1, 1)
FS1, FS0*
(0, 0)
100
AVAILABLE OUTPUT DATA RATES
(sps)
X2CLK = 0
200
FS1, FS0*
(0, 1)
20
25
X2CLK = 1
2.048
1.024
0
M0
1
Calibrate Offset:
In this mode the MAX1401 converts the voltage applied across CALOFF+
and CALOFF-. The PGA gain, DAC, and format settings of the selected channel (defined by
DIFF, A1, A0) are used.
0
0
1
Reserved:
Do not use.
1
Calibrate Gain:
In this mode the MAX1401 converts the voltage applied across CALGAIN+
and CALGAIN-. The PGA gain, DAC, and format settings of the selected channel (defined by
DIFF, A1, A0) are used.
Normal Mode:
The device operates normally.
1
0
M1
DESCRIPTION
CLKIN FREQUENCY,
f
CLKIN
(MHz)