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LM5176: Chip keeps breaking down when regulating 48V

Part Number: LM5176
Other Parts Discussed in Thread: CSD19502Q5B, LM5118, LM5170

Hi
I’m working with an LM5176 Evaluation Boardwith it acting as a boost converter. At the moment, I’ve been able to set the board up to regulate a 48V output with a 16V input with no load. However, whenever a load is set up, the LM5176 IC on the evaluation board breaks down. I’m unsure of why.


So far the set up has been replacing the secondary side fets Q5, Q7 with CSD19502Q5B N-Channel Fets, replacing the inductor with a 1mH inductor with a 500mA current rating as well as editing the control loop and soft start. The control loop capacitors, C28 to a 100pF cap and C22 to a .22uF. Soft start capacitor has been changed to a 1uF capacitor. The feedback loop off of the output voltage has also been changed such that R14 is 2 resistors at 243Kohms and R22 is an 8.25KOhm resistor.


The issues that came up even when the module was unloaded, the 2 mosfets on the secondary side have cross conduction issues. Current would spike during transitions as both fets would be on. One can see the gate’s on both the fets spiking, enough such that the bottom secondary fet turns on, and the sense resistor voltage would see spikes as well, up to 3V


Another issue that is seen is when probing across the gate and source of the secondary side fets, using a differential probe, specifically the Tektronix P5200, the IC keeps breaking.


Is there any more information that you would like in order to assist us?
What tips do you guys have?

  • Hi Kenneth,

    Thank you for using the LM5176. Would you please show us your schematic, and SW1 and SW2 waveforms? From there we can help debug.

    Thanks,
    Youhao Xi, Applications Engineering
  • Hi, with SW1 and SW2 they are currently both sitting at zero because the board is broken at the moment. The schematic is shown below. 

  • Your modification of the EVM circuit seeming making the circuit unstable.  Would you please use the LM5170 quick-start design tool to help you modify the EVM?  You need to follow the tool's results to select the CS resistor and compensation network, too.  By the way, is your load less than 0.1A?  You should consider the LM5118 for lower cost.

    Thanks,
    Youhao