• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 638 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC8760: load current capavility of DVDD

Shinichi Inoue
Guru 19931 points
Part Number: DAC8760
Other Parts Discussed in Thread: ISO7831

Dear Specialists,

My customer is considering DAC8760 and has a question.

I would be grateful if you could advise.

---

I am considering the circuit of DAC8760 Figure 96.

DVDD supplies to two ISO7831.

I am concerned about the supply current.

One of the ISO7831 uses for serial clk, CLK frequency is up to 12.5MHz(25Mbps), the maximum supply current may be 7.8mA.

Another ISO7831 is not for ALARM, CLR and LATCH, not so high, the maximum supply current may be  3.9mA.

The total supply current of two ISO7831 is 11.7mA.

On the other hand, supply current of DVDD is up to 10mA. 

The current of isolators exceeds the supply current of DVDD.

Does this means DVDD is not available in worst case?

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Mastermind 46290 points
    Shinichi-san,

    My best suggestion in this case would be to refer to Figure 14 in the datasheet which illustrates the DVDD internal LDO load regulation. For the most part the LDO appears to regulate it's output voltage well until seeing significant change at ~35mA.

    Of course, this is a typical curve so unit to unit behavior may vary slightly. Generally speaking datasheet parameters are heavily guard-banded and in this case the specific conditions of suggesting a 10mA "max" are ambiguous (i.e. was this based one 1%, 5%, 10%, etc. load regulation deviation?). Given that the total supply current required by the isolators is so close to the Electrical Characteristics table "max" along with the large over-head implied by the Typical Characteristics curves, I think this is a safe application of the isolators in tandem with the DAC8760 DVDD LDO.

    I can dig further into the conditions of the EC table specification, but in my opinion this should be perfectly okay.
  • 0 in reply to Kevin Duke
    Guru 19931 points
    Hi Kevin,

    Thank you for your reply.

    I understand load current of DVDD(10mA) should be considered not only Electrical Caracteristics, but also Figure 14.

    According to the Figure 14. , load current can supply up to 35mA, it may be no problem for supplying two isolators.

    I' ll share this information with the customer, and keep designing.

    I appreciate your great help.

    Best regards,
    Shinichi