ADS1246 datasheet(39/66 Pages) TI

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ADS1246

ADS1247

ADS1248

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SBAS426D – AUGUST 2008 – REVISED MARCH 2010

ADS1246 DETAILED REGISTER DEFINITIONS (continued)

VBIAS—Bias Voltage Register. This register enables a bias voltage on the analog inputs.

VBIAS - ADDRESS 01h

RESET VALUE = 00h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

VBIAS1

VBIAS0

Bits 7:2

These bits must always be set to '000000'.

Bits 1:0

VBIAS1:0

These bits apply a bias voltage of midsupply (AVDD + AVSS)/2 to the selected analog input. Bit 0

is for AIN0, and bit 1 is for AIN1.

0 = Bias voltage not enabled (default)

1 = Bias voltage is applied to the analog input

MUX—Multiplexer Control Register.

MUX - ADDRESS 02h

RESET VALUE = x0h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

CLKSTAT

MUXCAL2

MUXCAL1

MUXCAL0

Bit 7

CLKSTAT

This bit is read-only and indicates whether the internal or external oscillator is being used.

0 = Internal oscillator in use

1 = External oscillator in use

Bits 6:3

These bits must always be set to '0000'.

Bits 2:0

MUXCAL2:0

These bits are used to select a system monitor. The MUXCAL selection supercedes selections

from the VBIAS register.

000 = Normal operation (default)

001 = Offset calibration. The analog inputs are disconnected and AINP and AINN are internally

connected to midsupply (AVDD + AVSS)/2.

010 = Gain calibration. The analog inputs are connected to the voltage reference.

011 = Temperature measurement. The inputs are connected to a diode circuit that produces a

voltage proportional to the ambient temperature of the device..

Table 23 lists the ADC input connection and PGA settings for each MUXCAL setting. The PGA setting reverts to

the original SYS0 register setting when MUXCAL is taken back to normal operation or offset measurement.

Table 23. MUXCAL Settings

MUXCAL[2:0]

PGA GAIN SETTING

ADC INPUT

000

Set by SYS0 register

Normal operation

001

Set by SYS0 register

Offset calibration: inputs shorted to midsupply (AVDD + AVSS)/2

010

Forced to 1

Gain calibration: VREFP – VREFN (full-scale)

011

Forced to 1

Temperature measurement diode

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