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Inquiry regarding Operating Current on LM5027A

Atsushi Okui
Genius 4015 points

Hello,all

Now we have one inquiry regarding Operating Current on LM5027A from our customer.

Please refer to the item below, and feedback us with your comment.

When referring to the "Electrical Characteristics" on datasheet page5, this parameter is described as Ibias, and seems to be related with UVLO.

Please let us clarify how we could reduce this current with setting UVLO.

We thank you in advance for your information.

Best regards,

  • 0
    TI__Expert 5900 points

    Hi Atsushi,

    If you want the converter be in switching mode, you can not decrease the Ibias by setting UVLO.

    In the electrical table for Ibias, the condition "COMP and VCC Open, UVLO and OTP = 3V " is to guareentee that controller  work in switching mode.

    However, what is customer's concern? if they connect VCC pin to other source just like figure1 in spec, then they don't need to worry about the Ibias. The Ibias would be very very small when there is external source connected to VCC.

    Regards

  • 0 in reply to Kening Gao
    Genius 4015 points

    Hello, thank you for your prompt reply.

    With regard to the detailed configuration, I could have some feedback from them.

    We are designing the circuit based on datasheet Page 27 "Figure 34. Application Circuit".

    Actually, VCC is supplied from T1 (upper side) on this figure, but VIN and VCC are short connected. The VCC input level from T1 is about 12~13V.

    Also, there are pre-regulator circuit configured by transistor and Zener diode (Clamped on 11V), in front of J1(Vin). The input level from this pre-regulator is less than 15V.

    Also, we have one additional inquiry from them, please refer to the item below and feedback us with your comment.

    Please let us clarify how much Ibias consumption would be, in case of UVLO=0~0.4V, UVLO=0.4~2.0V and 2.0V~ individually.

    We thank you once again for your information.

    Best regards,

  • 0 in reply to Atsushi Okui
    Genius 4015 points

    Kening-san,

    With regard to the additional inquiry above, we would appreciate if you could let us know your current situation for verification. 

    We are looking forward to hearing from you by return.

    We thank you once again for your information.

    Best regards,

  • 0 in reply to Atsushi Okui
    TI__Expert 5900 points

    Hi Atsushi-San,

    I am not clear at what you said"Also, there are pre-regulator circuit configured by transistor and Zener diode (Clamped on 11V), in front of J1(Vin). The input level from this pre-regulator is less than 15V."

    I am worried about that at sometimes, the pre-regulator circuit would sink lot current from VCC. I hope i was wrong. if you can attach a circuit to illustrate the connection, it would be better.

    Refer to your questions,

    First, we need to clarify the "Ibias", In the datasheet, Ibias means the current of Vin pin. And this value was varied with the switching fequency/ load etc.. The value in datasheet is only tested at certain condition.

    1. UVLO=0~0.4V.  Ibias is bout 310uA

    2.UVLO>2V, the Ibias is about 6.8mA.

    3.UVLO=0.4~2.0V, There is on such value in datasheet. From my experience, the value wuld be less than 1mA. compared to situation2, VCC and REF reguatators are enabled here.

     

    I don't know the aim of this inquiry. I think compared to the whole system loss, the consumpation on IC is very low. even with 1mA Ibias at 12V , the consumpation is only about 12mW.

    Regards

     

     

  • 0 in reply to Kening Gao
    Genius 4015 points

    Kening-san,

    Thank you for your reply towards the inquiry regarding LM5027A from our customer.

    With regard to the schematic of pre-regulator circuit, we can send you this, but this is a customer proprietary data.

    Please let me communicate with you directly via e-mail in order to have further proceed.

    We thank you once again for your information.

    Best regards,

  • 0 in reply to Atsushi Okui
    TI__Expert 5900 points

    Hi,

    My email is Kening-gao@ti.com

     

    Regards

  • 0 in reply to Kening Gao
    Genius 4015 points

    Kening-san,

    Thank you for your support regarding inquiry regarding LM5027A from our customer.

    Please let me confirm whether you could receive the schematic which was sent on Aug 25th.

    We thank you once again for your information.

    Best regards,