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ADS8028: ADS8028IRTJT

Roberto Botticelli
Prodigy 10 points
Part Number: ADS8028
Other Parts Discussed in Thread: REF5025, REF5040, LM4140

I'm looking to substitute the obsolete Analog Device max1298 ADC with the TI ADS8028.

In max1298, the 5V analog input span is obtained from a 2,5V voltage reference.

with the ADS8028 ADC I want use a 4,096 voltage reference and it is not possible to enable the ADS8028 external voltage reference after disabling the internal voltage reference of the ADS8028.

1) in EVM datasheet 
https://www.ti.com/lit/ug/sbau198a/sbau198a.pdf?ts=1706520965337

at pg.10 it is written:

"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".

At the same time, in the EVM electrical scheme the external Vref can be directy connected to the ADC Vref input.

also in the ADS8028 data sheet this warning is reported and the ref5025 is suggested, but in this case the VREF is 2,5V (the same of the internal reference.

I wish to use the external reference ADR444B (Analog Device)  about 4V voltage reference   (High output source and sink current +10 mA and −5 mA, respectively).

I need help to find the right interconnection scheme to use the 4,096 V voltage reference in input to the ADS8028 Vref pin.

thank you in advance for your help.

  • 0
    TI__Guru**** 172836 points

    Hi Roberto,

    Welcome to our e2e forum! 

    With the recommended reference capacitor on the ADS8028, it will take about 5mS for the cap to charge.  You can write to the digital interface roughly 500uS after digital power is established so you would only see a short transient increase in current draw.   You might also consider a device like the REF5040, which has the 4.096V that you are looking for and it also features an enable pin.  You can power up the ADS8028 and then use a GPIO to enable the external reference as part of your initialization routine.

  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    Hi Tom,

    Thank you for your help.

    an external votage reference delayed it's a good idea, unfortunately the ads8028 will be placed on a my daugther board and no more control signals are available to manage the delayed external voltage reference.

    In REF5040 datasheet i can't find the enable pin, so I do not understand what means "REF5040, which has the 4.096V that you are looking for and it also features an enable pin".

    would you like help me on this topic?
    Can you suggest to me a well suited external voltage reference for my application provided of an enable pin (SOIC8 if possible)?


    Thank you in advance for your help.

  • +1 in reply to Roberto Botticelli
    TI__Guru**** 172836 points

    Hi Roberto,

    Sorry about that - take a look at the LM4140, 

  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    Hi Tom.

    tank you for your help.