• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 871 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.

LM5008: LM5008 : No load Power Dissipation

Gaayathri Nagarajan
Intellectual 270 points
Part Number: LM5008

Hi,

I would need to know what contributes to no load power dissipation for LM5008 IC.

(i.e) calculations involved in no load power calculation with respect to DC switching regulator ICs.

As far as I know, we have power losses in

1.Internal MOSFET

2.Feedback resistors

 As per energy star requirements, the no load power dissipation should not cross 30mW. Is it advisable to use this IC for attaining dissipation < 30 mW?

  • 0
    Intellectual 270 points
    Hi,


    With reference to my above query, the power supply requirements are as follows:
    Vin : 30 - 77V
    Vo : 18V
    Io : 65mA

    Thank you.
  • 0 in reply to Gaayathri Nagarajan
    Intellectual 270 points
    Hi,

    Can you please address my queries above?
  • 0 in reply to Gaayathri Nagarajan
    TI__Guru**** 191445 points

    Let me see if I can find someone to assist you.  Please be advised it is holiday season in the US, so any response may be delayed.

  • 0
    TI__Intellectual 2320 points

    Hello Gayathri,

    With the LM5008, I expect the part to have an estimated power dissipation close to ~50mW  at 65mA and 30VIN. For higher VIN, we expect the IC loss to go up to 120mW.

    These numbers are derived from WEBENCH based on your input/output parameters.

    The main sources of the power losses across the IC can be chiefly attributed to:

    1.High side MOSFET Conduction and switching losses.

    2. High side Gate drive losses

    3. Iq losses(non switching losses due to the internal logic blocks)

    The feedback losses should be treated as external losses to the IC.

    Regards,

    Sourav

  • 0 in reply to Sourav.Sen
    Intellectual 270 points
    Hi Sourav,

    Agreed. Thanks for the reply.

    But I would like to know about the worst case losses during no load.
    The web bench provides the losses during loading.
    As far as I know, Iq losses contribute to no load losses. Apart from this, do we have any other losses?

    Thanks & Regards,
    Gaayathri
  • 0 in reply to Gaayathri Nagarajan
    TI__Intellectual 2320 points

    Hello Gaayathri,

    If you are accounting for just the no load losses, then you are correct in taking into account the Iq losses. However this would be just the Iq non switching losses (VIN*Iq) where Iq is the operating non-switching input current which you can check rom the EC table. However, in a Buck closed loop no load case, as in the COT Buck converter like the LM5008, there is still the need of the pre-load current (~1mA) in order to maintain the regulated output. At such light load, there will still be at least one switch node on pulse (high side conduction + switching loss)  followed by the gate drive loss. However the  contribution of these should be relatively insignificant.

    Regards,

    Sourav