Temperature=V

EXT_REF

ADC_Code

10

+109.3 - 273.15

Temperature = V

EXT_REF

ADC_Code

4096

-

10

+ 109.3 - 273.15

Positive Temperature =

ADC_Code

4

Negative Temperature =

4096

ADC_Code

-

4

ADS8028

www.ti.com

SBAS549B – MAY 2011 – REVISED MARCH 2012

If the output data MSB is ‘0’, the temperature can be calculated with Equation 3:

where:

VEXT_REF is the value of the external reference voltage

(3)

If the output data MSB is ‘1’, the temperature can be calculated with Equation 4:

where:

VEXT_REF is the value of the external reference voltage

(4)

For a 2.5-V reference (internal or external), Equation 3 and Equation 4 simplify to Equation 5 and Equation 6,

respectively.

(5)

(6)

REFERENCE

The ADS8028 can operate with either an internal voltage reference or an optional external reference. The type of

reference used is set by the EXT_REF bit in the Control Register.

The internal reference is selected when the EXT_REF bit is set to '0'. A 2.5-V output of the internal reference is

available on the REF pin. A 10-µF decoupling capacitor is recommended between the REF and AGND pins. The

reference circuit requires 5.5 ms to charge the decoupling capacitor. The internal reference is capable of

sourcing up to 2 mA of current and is designed to drive the ADS8028. It is recommended to buffer this output for

use elsewhere in the system.

The ADS8028 can operate with an external reference when the EXT_REF bit is set to '1'. An external reference

can be supplied through the REF pin. By default, the ADS8028 powers up in internal reference mode and must

be programmed to function with an external reference. Until such a time, the ADS8028 draws additional current

from the external reference source. This current is limited to 20 mA, using internal protection circuitry. Texas

Instruments' REF5025 can be used as external reference source for the ADS8028.

Copyright © 2011–2012, Texas Instruments Incorporated

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