Datasheet

ADS8028EVM Hardware Details

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3.4 Voltage Reference

The ADS8028EVM allows the user flexibility to select different voltage reference sources for the ADS8028.

Options include the:

• ADS8028 internal 2.5-V voltage reference,

• Onboard REF5025 2.5-V reference, or

• External reference source

When the ADS8028 powers up, the internal 2.5-V reference is selected as the reference source by

default. To use an external reference source, the internal voltage reference must be disabled by

performing a serial interface write to the ADS8028 control register to update bit 2. When using an external

source, shorting pins J-REF.1-2 uses the REF5025 external 2.5-V reference. If a reference voltage other

than 2.5 V is needed, the REF5025 can be replaced with any other reference in the REF50xx family.

Shorting pins J-REF.2-3 connects J-ANALOG.20 to the ADS8028 reference input. This short allows the

user to output the internal ADS8028 voltage reference to another circuit or allows a external reference

voltage to be applied to the ADS8028 reference input when the internal reference is disabled. The

allowable voltage range for an external voltage reference is 1 V to AVDD (5 V when the ADS8028EVM is

used with the MMB0).

Figure 7. EVM Voltage Reference Schematic

CAUTION

The user should avoid connecting any external voltage reference to the

ADS8028 before a serial write to the ADS8028 control register disables the

internal reference source. Providing an external source prior to this

communication draws additional current from the external source. The

ADS8028 internal protection circuitry limits this current to 20 mA.

ADS8028EVM-PDK SBAU198–April 2012

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