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Original question:

LM5143-Q1: output shutdown in M5143 disabled

LM5143-Q1: LM5143 output 1 channel abnormal issue

Eason Yuan
Intellectual 840 points
Part Number: LM5143-Q1
Other Parts Discussed in Thread: LM5143,

Hi Team,

Could you please check the schematic as attached.

Now our board work abnormally in 3.3V output. Thanks!

  • 0 in reply to Eason Yuan
    TI__Intellectual 840 points

    For 3.3V output, the output ripple is very big which cause the inductor and capacity high temp with the zero load.

  • 0 in reply to Eason Yuan
    TI__Mastermind 34875 points

    Hi EAson,

    Pls check your circuit design by LM5143 Calculator:

    https://www.ti.com/tool/LM5143DESIGN-CALC

    Pin2 & 29 COMP network should be designed according to actual Cout and ESR.

    What's saturation current of L38 and L39? how about load current? seems R634 and R639 2mohm is too small which set OCP at 35A!

    B R

    Andy

  • 0 in reply to Andy Chen
    TI__Intellectual 840 points

    Thanks your reply, Andy.

    We change the pin 34.(Mode pin).  It worked well after we connect a 10-kΩ resistor between MODE and AGND.

    Pin 34 -MODE---Connect MODE to AGND or VDDA for dual-output or interleaved single-output operation, respectively. This also configures the LM5143-Q1 with an EA transconductance of 1200 µS. Connecting a 10-kΩ resistor between MODE and AGND sets the LM5143-Q1 for dual-output operation with an ultra-low IQ mode and an EA transconductance of 60 µS.

    Could you please explain the pin function for this schematic? 

    Why the pin 34 connect to AGND, the 3.3V output met issue and the 5V output work well.

    But both outputs work well Iafter we connect a 10-kΩ resistor between MODE and AGND.

    BR

  • 0 in reply to Eason Yuan
    TI__Mastermind 34875 points

    Hi Eason,

    the control loop cross over freq Fx is proportion to the EA transconductance, reverse proportion to Vout, the 3.3V loop maybe unstable on present design because of too high Fx or no enough phase margin, reduce EA transconductance from 1200us to 60us will heavily decrease the Fx and improve phase margin, 

    You can check if the SW waveform is stable on 3.3V rail on original circuit.

    reduce R339 from 22K to 2.2K,  C830 from 47pF to 470pF may also make 3.3V rail operation more stable.

    B R

    Andy