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Can the AD5735 be used in single supply configuration?

I received this inquiry from a customer:

In our design the AD5735 will only be used in a unipolar output mode, therefore I would like to know if the AD5735 AVss pin can be tied to gnd instead of a negative supply. I would prefer not to have to add a negative supply to the design if it is not necessary.

The datasheet list the range for as -10.8 <= AVss <= -26.4. 

  • Is there any way to make the AD5735 work correctly without a negative supply? 
  • If not, how much current should the negative supply be capable of sourcing/sinking? 
  • Any suggestions for generating the required negative supply.
  • Hi Lionel,

    Q. The datasheet list the range for as -10.8 <= AVss <= -26.4.

    Is there any way to make the AD5735 work correctly without a negative supply?

    A. The AD5735 uses a –Vsense buffer which requires extra footroom, hence the AVSS voltage requirement. As such, the AD5735 has not been characterised with a unipolar supply and specifications cannot be guaranteed.

    That said, the AD5755-1 (16-bit current and voltage output DAC) does not use a -VSense buffer (replaced with a CHART pin) therefore it has been characterised with unipolar supplies.

    AD5757 and AD5737 are also unipolar supplied DACs however they are current output only.

    Q.If not, how much current should the negative supply be capable of sourcing/sinking?

    A. AISS consumes a maximum of -11mA in voltage mode when the output is unloaded. See power requirements in Table 1 of the datasheet  for the full list of power requirements.

    Q. Any suggestions for generating the required negative supply.

    A. The power management group will be better able to assist you with this query. However keep the AD5755-1 in mind as it is compatible with unipolar supplies.

    http://ez.analog.com/community/power

    FAQ on generating Negative Supplies:

    http://ez.analog.com/docs/DOC-6379

    Regards,

    David

  • David,

    Thanks for the quick and comprehensive response.  I'll pass this data along to the customer and see what he thinks.

    LA

  • David,

    Here is some additional customer feedback.

    Thanks for getting back to me quickly with answer to my question, but just so you know I have the AD5755 eval board running in a unipolar supply configuration without any problems so far. I’ve got the –Vsense pins connected to analog  gnd and +Vsense pins connected to their respective +Vout pins, so I thought if the AD5755 was working in this configuration why wouldn’t the AD5735 work also since it’s just a 12Bit version of the AD5755 part.

    LA

  • Hi Lionel,

    The AD5755 may be functional but we cannot guarantee the part's behaviour or performance if the user does not follow the conditions as outlined in the specifications in each datasheet.

    My recommendation still is to use the AD5755-1, which has been characterised for unipolar supplies or to consult with the power management group about the possibility of adding a negative supply.

    Regards,

    David

  • Hi Lionel,

    Both the AD5755 and AD5735 have the -Vsense Buffer, no issues here but my response earlier covers both these products. A bipolar supply is required at all times.

    The AD5755-1 replaces it with CHART for HART functionality.

    The AD5757 and AD5737 are current output only DAC's

    Regards,

    David

  • David, I had one more customer inquiry come in before receiving you latest reply.  I think this is more of a curiosity question.

    Both the AD5735 and AD5755 have the –Vsense buffer according to the specs.  They also have the same min, max requirements for Avss.  So if they removed the –Vsense buffer, the datasheet doesn't reflect that.  Can you verify this with the factory folks?

  • Hello Pooja,

    Question no. 1 - so i guess i can achive volatge and current output from this AD5735 DAC simultanesouly.Please coorect me if i am wrong?


    The AD5735 is a quad channel part (Channel A, B, C, D), every channel has a voltage and current output. You can enable the voltage OR current output on each channel, not both. So for example, on channel A I can have current output and on channel B I can have voltage output. Channel A can't have a voltage output and current output at the same time.

    Question no.2 - how  many current and volatge channel can be enable at a time.?

    All four channels can be enabled at the same time. As mentioned in the previous answer, you can only choose voltage or current on each channel.

    Question no. 3 - after getting volatge and current output , i need to give this output to a connector,so i can directly give output to the connector or after getting output from the DAC, i need to add some other circuit in between DAC and connector.for an example i have gone through application note AN1289( few methods are given there to control the power dissipiation of the current output,is there any circuit is required for volatge also?).

    Power dissipation is one important aspect, but if users will directly access the DAC output pins, i'd recommend some output protection circuitry. I'd recommend looking at CN-0328 as it has some examples of how to set up this circuitry.

    Question no. 4 - input for thie DAC will internal or external reference volatge( that is 5V) what is current limit for internal reference?


    You have a choice of either the internal reference or external reference. Internal reference means less discrete circuitry but an external reference gives higher precision. It's up to your application which is the best choice.

    The AD5735 REFIN pin is internally buffered, there should be negligible current drawn from the voltage reference.

    Regards,

    David

  • Hi David

    I am Pooja, working in Quest-Global india.

    I am working on application using DAC AD5735 and my requirement is 2 different channel configuration,

    1. channel bipolar volatge output(+10 & -10 at a time)

    2. unipolar current ouput(4-20mA) and unipolar volatge output (5V).

    Question no. 1 - so i guess i can achive volatge and current output from this AD5735 DAC simultanesouly.Please coorect me if i am wrong?


    Question no.2 - how  many current and volatge channel can be enable at a time.?

    Question no. 3 - after getting volatge and current output , i need to give this output to a connector,so i can directly give output to the connector or after getting output from the DAC, i need to add some other circuit in between DAC and connector.for an example i have gone through application note AN1289( few methods are given there to control the power dissipiation of the current output,is there any circuit is required for volatge also?).

    Question no. 4 - input for thie DAC will internal or external reference volatge( that is 5V) what is current limit for internal reference?

    Can you please reply to these questions ASAP?

    A Big Thanks in Advance.

    Awating for your reply.

    Regards

    Pooja

  • Thank You so much david for your prompt reply.

    Regards

    Puja