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LM27402: 12-V to POL 1 MHz, external gate driver, synchronous buck controller recommendation

Novantiv
Prodigy 20 points
Part Number: LM27402
Other Parts Discussed in Thread: CSD86350Q5D, LM27403EVM-POL600, TPS53632, LM27403

Tool/software:

I am working on a POL module that can do 12V-1V (and other standard POL output voltages). I like the design in  LM27403EVM-POL600 and also the one in this app note that uses LM27402 and csd86350q5d:

High Density PCB Layout of DC/DC Converters, Part 2

Do you have any recommendations for a controller that meets the following:

  1. Synchronous buck controller
  2. No integrated gate driver (just digital output, like the TPS53632 PWM pins)
  3. Voltage mode
  4. 500 kHz ~ 1200 kHz
  5. Same or similar features as LM27402

I am looking for flexibility in selecting gate driver/MOSFET combinations or power stages.

Kindly also comment on any performance downside to using the LM27402 output as logic signals only, connecting LG and HG to, for example, LI and HI inputs of a half-bridge driver.

Thank you

  • 0
    TI__Mastermind 21210 points

    A dcdc controller parameter search table is here AC/DC & DC/DC controllers (external FET) product selection | TI.com.   

    I really do not have a recommendation for a controller as most controllers were developed/released awhile back and the trend is to integrate more and more into devices. 

    Most current product developments in my group are converters (controller +fets) or power modules (converter + inductor).    However, the LM27403 and LM27402 are still popular but as you state have the driver integrated.    I do not know of any technical drawbacks of using the integrated driver as a logic signals only, the boot cap and diode would need to be used.   The gate drive logic circuit is designed to prevent both high side and low side  fet from being on at same time.     If the integrated drivers can drive external fets I am assuming the driver can drive and external driver since the capacitance load should be lower. 

    My group supports some of the products in the search table and other groups may have different product roadmaps.    The TPS53632 is in different group and if you see a device in the table, you can post here and the thread can get redirected to proper group or open a new thread and the e2e system will sort to product group. .         

  • 0 in reply to David_Daniels
    Prodigy 20 points

    Understood. Thanks.

  • 0 in reply to Novantiv
    TI__Mastermind 21210 points

    I discussed the int gate driver use case with a coworker and mentioned depending on the controller used, sometimes the SW node voltage is sensed to determine the current limit.

  • 0 in reply to David_Daniels
    Prodigy 20 points

    Thanks for this additional reply. Yes, I figured that if we want to keep that functionality, we need to keep the SW pin of the controller and Switch node of the half bridge (HS driver return) at the same potential.

    I may have missed it in the LM27402 -- can the current sense pins simply left floating (or maybe shorted together?) if not using the current sense feature?

    Lastly, is there a way to purchase the LM27402 -based POL module in this app note? https://www.ti.com/document-viewer/lit/html/ssztc68 or at least be able to download design files? I did not find in the store nor as a reference design.

    Thanks!

  • 0 in reply to Novantiv
    TI__Mastermind 21210 points

    The LM27402 board in the app note was not released as a standalone evm, so I cannot find any archived files.  

    There is a different LM27402 board  available https://www.ti.com/tool/LM27402SQEVAL it was released in 2012. 

    However the LM27403 has two evms, https://www.ti.com/tool/LM27403EVM and   https://www.ti.com/tool/LM27403EVM-POL600.   The POL600 is a similar high density design in the app note, though slightly bigger.  

    If interested in gerber files, accept the e2e friend request and I share the gerbers I have in the e2e mail system. 

    The LM27402 uses the DCR sensing method with CS+ CS- pins for current limit so I do not think it will use the SW node.        But since this concept is not the typical use case, I am not sure if the sw node is used for other circuits or features.     

    I think you can ground the SW node and use the HG as the pwm output signal to gate driver and leave LG open.   To defeat the current sense, I think shorting CS+ to CS- will work.

  • 0 in reply to David_Daniels
    Prodigy 20 points

    Hi David,

    Thank you very much for the thorough response. Yes, the gerbers will be much help. I accepted the e2e friend request.

    Wish me luck!