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LM5175: OVP spec of LM5175 and LM5176

Shinichi Inoue
Guru 21721 points
Part Number: LM5175
Other Parts Discussed in Thread: LM5176

Dear Specialists,

My customer is considering LM5175 and LM5176.

He has inquries about OVP spec.

I would be grateful if you could advise.

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(1)Could you tell me the Min / Max value for the specification of the output overvoltage protection (OVP) function of the LM5175 and LM5176?

(2)If output overvoltage protection works, will all four switch FETs be stopped or which one of the four stops?

(3)How much delay time between detection of OVP and stop of FET?

(4)I'd like to use adjusting output voltage.

Is there a possibility of damage to FET and Rsense when the output voltage change from 24V to 12V.

When voltage change happened, OVP occur at that time, so is there a possibility of reverse current flow from output to low side FET.

Can LM5175 and LM5176 protect such condition?.

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    TI__Guru* 78470 points
    Hi Shinichi,

    Answers to your original questions (sorry I do not copy and past them here):
    (1) We only have typical values, these are guaranteed by design but not particularly tested during characterization.
    (2) During OVP event, all FETs stop.
    (3) The delay time is not characterized, but it should not be longer than 1us.
    (4) This is a very good question. It would not damage the Rsense nor the FETs, but if you adjust Vout by controlling the FB voltage, a too fast change would induce an OVP event, and the operation would stop, and restart later. To prevent such interruption, the control of the voltage adjustment should be applied gradually, allowing a transition time.

    In such cases, reverse current would flow from the output to input. Yes the low side buck switch may have some voltage stress. However, it is naturally clamped by the high side body diode.

    In short, yes the LM5175/76 protect such condition. Make sure your layout is optimized (see our datasheet and evm example) to allow the high side FET body diode to be effective.

    Thanks,
    Youhao
  • 0 in reply to Youhao Xi
    Guru 21721 points
    Hi youhao,

    Thank you for your quick reply.

    I'll share your suggestion with the customer.

    If the customer has an additional question, I consult you again.

    I appreciate your great help and cooperation.

    Best regards,
    Shinichi