• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 62 subscribers
  • Views 432 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.

LM5064 VDD source current

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: ISO1540, LM5064

Please tell me about VDD voltage regulation.
According to datasheet, VDD is 4.6V to 5.15V at IDD=0mA, then VDD is 4.8V typ at IDD=-10mA.
Do you have the voltage accuracy data when IDD=-10mA? We would like to know min and max value.

And is it allowed that more than 10mA current flows from VDD? Or should we limit the VDD source current up to 10mA?
We are considering about pull-up resistor of PMBus line with ISO1540. About 15mA(max) is required when pull-up resistor is 1k.

Best Regards,
Kohei Sasaki

  • 0
    TI__Genius 12380 points
    Hi Kohei,

    We recommend keeping the current flow on Vdd to a minimum. The main reason is power dissipation. If Vin = 54V, then 15mA draw for example would be 50V * 15mA = 750mW of power dissipation. This is quite high for the LM5064, which has a junction to case thermal coefficient of 4C/W.

    The LM5064 EVM uses SI8400 attached to the Vdd pin along with 10k pull up resistors for the SDA and SCL.

    If the customer is using the ISO1540, we would recommend using 10k pull up resistors as well, if possible. I am not an expert on I2C pull-up resistor selection, but they may check out this app note:
    www.ti.com/.../slva689.pdf

    Based on this information, it is my understanding that the pull up resistor value depends on their desired I2C bus speed, as well as their bus capacitance. As long as they run the speed at 100kHz or less and keep the bus capacitance at 100pF or less, then 10k resistors should be good (according to my interpretation of this app note).

    If not 10k, then we recommend using as large of pull up resistors as possible, consider the power dissipation of the LM5064, and plan for thermal heatsinking accordingly.

    As for accuracy, the Vdd should have little to no effect on the accuracy. The accuracy relies more on the Vref voltage, which is regulated down to 2.97V, after the Vdd regulator. It's possible that if you load the Vdd voltage greater than 10mA, that it may affect the Vreg voltage and cause a slight telemetry change (but we have not spec'd this).

    Thanks!
    Alex