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LM5121-Q1: High Power Solution

Umberto Frangi
Expert 4045 points
Part Number: LM5121-Q1
Other Parts Discussed in Thread: LM5122, LM5122-Q1, LM5121

Hi,

 I need to make a proposal for a power supply section, dedicated to an automotive audio system.

The most critical conditions are Vin=10V, Vout=34V, Iout=20A .

Do you have a reference design or/and a TINA simulation with these parameters?

I suggested to do it with multiphase LM5122, but due to cost reason, I am not sure this will be accepted.

Thanks

Umberto

  • 0
    TI__Guru* 78200 points
    We have a ref design with the multiphase LM5122-Q1 just for automotive audio amplifiers, with envelope tracking implemented with a simple external circuit. Please contact Max Dai (x-dai@ti.com) for details.
  • 0 in reply to Youhao Xi
    TI__Expert 4045 points
    Thanks for the info.
    But in your opinion which is the highest output current could be achieved with LM5121, with given Vin, Vout?
    Umberto
  • 0 in reply to Umberto Frangi
    TI__Guru* 78200 points
    For single device, the LM5121 and LM5122 can handle the same power. However, since the driver capability is 3A, one device cannot easily deliver your 680W load power. Multiphase is needed and hence the LM5122 should be selected.
  • 0 in reply to Youhao Xi
    TI__Guru* 78200 points
    Sorry I might misunderstand your question. The LM5121/LM5122 each can do up to 200W.
  • 0 in reply to Youhao Xi
    TI__Expert 4045 points
    Thanks, but suppose you add a PNP/NPN stage for each of the external MOSFETs to increase driving capability, can we go up to>500W?
    Umberto
  • 0 in reply to Umberto Frangi
    TI__Guru* 78200 points
    Theoretically the answer is yes, but there are a few things to consider.

    (1) the LM5121/22 uses adaptive dead time scheme. The internal drivers cross check each other's output to avoid mutual turn-on of the external high and low side FETs. Adding an external driver defeats the adaptive dead time scheme and shoot-through of the external FETs may occur.

    (2) input current for single phase will be high, and you have to select a very small current sense resistor. At less than full load but still at a fair level, the current sense signal will become very small, subjecting to noise effects.

    (3) concentrated heat issue.

    By the way, do you explain why you prefer LM5121 to LM5122?
  • 0 in reply to Youhao Xi
    TI__Expert 4045 points

    Hi Youhao,

     the customer would like to use a single stage for cost reasons and LM5121 provides input disconnect circuitry.

    I explained that 700 W is not achievable with it and now they are reconsidering the specs.

    I started to do some simulations with TINA and the attached file, but some results are not very clear to me.

    Can you check, running transient analysis?

    Thanks

    Umbertowebench_design_26664_884.tsc

  • 0 in reply to Umberto Frangi
    TI__Guru* 78200 points
    Hi Umberto,

    Sorry somehow this is overlooked. You can always send email to me if the reply is delayed. Anyway, we will not recommend the LM5121 for 700W application because it is not suitable and we are not able to support such application. Between the two options, the L5122 is the way to go with multiphase sharing, and you can use a hotswap device in the LM506x family for load disconnect control.

    Thanks,
    Youhao