• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 314 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LM74700-Q1: Max Power dissipation in operation

Takashi Onawa
Genius 13200 points
Part Number: LM74700-Q1

Hi Team,

Could you tell me Max power dissipation of LM74700 in normal operation?

Is it only 130uA(Operating Quiescent Current) or do we need to take account into  "Enable sink current" and  other parameters for the calculation? 

Regards,

Takashi Onawa

  • 0
    TI__Genius 16305 points
    Hi Takashi,

    Yes 130 uA is current taken from input and you need to include cathode current and EN sink current as well.
    But those are very small currents.


    Regards,
    Kari.
  • 0 in reply to Karikalan Selvaraj
    TI__Genius 13200 points

    Hi Karikalan-san,

    OK, I understood that the current consumption will be around 135uA in normal operation.

    Sorry I have two more question. I need to clarify the peak current consumption also.

    1. The "Operating Quiescent Current" include CP current for charging FET's gate also?

    2.  Why does the Iq go up more than 4 times under low power supply condition shown following graph?

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    TI__Genius 16305 points
    Hello Takashi,

    Charge pump operates by taking power from Vanode.
    For example, charge pump delivers 300uA to VCAP current at Vanode 12V, but to deliver 300uA it takes 1.4mA current (short time) from Vanode.

    Charge pump is turned ON/OFF to reduce the average Iq current, at VCAP-Vanode reaches 13V, charge pump is turned off, then due to leakage VCAP-Vanode discharges and when it reaches 12.1V, charge pump is turned on (13V and 12.1 V are specified in datasheet page 6). Iq current will see a pulsed behavior when charge pump turns ON/OFF. Average Iq current is mentioned in the datasheet. When the charge pump is ON, it takes 1.4mA (typical) from Anode. Actual current into VCAP is 300uA. Ratio of 1.4mA/300uA = 4.67. So 4.67x current is taken from Vanode due to charge pump.

    Now, coming to your question, when Anode voltage is lower, at 3.2V, charge pump voltage is 8V maximum (speficied in page 6 of datasheet).
    It cannot reach 13V or 12.1V. Due to this charge pump is not turned off and it remains on always. And now at 3.2V, charge pump current is about 80uA and at low Vanode ratio of Iq current to charge pump current is more than 4.67x calculated above and so we about 500uA current (typical) at 3-4V Vanode.

    Regards,
    Kari.
  • 0 in reply to Karikalan Selvaraj
    TI__Genius 13200 points
    Hi Karikalan-san,

    OK, i understood the 130uA Ip includes charge pump current and peak current will be around 1.4mA max. Due to not turning on CP at low voltage range, the Iq will be higher like 500uA.

    Is this understanding correct?


    Regards,
    Takashi Onawa
  • 0 in reply to Takashi Onawa
    TI__Genius 16305 points
    Hi Takashi,

    Yes, your understanding is correct.
    At low voltage input, charge pump turn on/off operation is not seen, so higher Iq current.
    At high voltage, charge pump turn on/off to reduce Iq current.

    If your question is answered, click "this resolved my issue" button at the end.

    Regards,
    Kari.