Rainbow-electronics MAX1400 Bedienungsanleitung PDF herunterladen (Seite 15)

MAX1400

+5V, 18-Bit, Low-Power, Multichannel,

Oversampling (Sigma-Delta) ADC

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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) Burnout 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

burnout 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.

Default condition is in bold print.

Table 3. Special Modes Controlled by M1, M0 (SCAN = 0)

DESCRIPTIONM1

Normal Mode: The device operates normally.

Calibrate Gain: In this mode the MAX1400 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.

Reserved: Do not use.

Calibrate Offset: In this mode the MAX1400 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.

1.024

CLKIN

FREQ.

2.048

X2CLK = 1

CLKIN

(MHz)

CLKIN

FREQ.

2520

FS1, FS0

(0, 1)

(sps)*

200

X2CLK = 0

CLKIN

(MHz)

AVAILABLE OUTPUT DATA RATES

100

FS1, FS0

(0, 0)

(sps)*

FS1, FS0

(1, 1)

(sps)

FS1, FS0

(1, 0)

(sps)

1.024 2.048 5040 400200

1.024 2.048 10080 800400

1.024 2.048 200160 1600800

2.4576

4.9152

50 600300

2.4576 4.9152 120100 1200600

2.4576 4.9152 240200 24001200

2.4576 4.9152 480400 48002400

CLK

MF1

MF0

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 35 36

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