• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 757 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5180-Q1: How to resolve stability issues of standard Flyback configuration

Lasto Roma
Intellectual 600 points
Part Number: LM5180-Q1
Other Parts Discussed in Thread: LM5180, , TPS2662

We have a prototype where we are connecting TPS2662 output to standard flyback configuration using LM5180 with EMI filter (for isolated 13.5V output), as shown in the schematics below.

The output of the TPS2662 (which is the input of LM5180) is oscillating at 200 msec (charging and discharging cycles, with ppk = 2.16V around  5.75V). The supply voltage is 12.6V from batteries. The waveforms are shown below.

What changes should we make to the  LM5180 circuits below to resolve the instability issues?

Also, the output of the Flyback is 14.9V at no load, but it goes down to 6.5V if we connect 200 Ohm dummy load. 

Please let me know if you'd need further information (PCB layout or  settings used in TI design tools).

Thank you.

LM5180-Q1 Flayback Schematic (Standard)

TPS2662 Protection Schematics (Standard)

Waveforms (@500 msec/div)

Waveforms (@50 msec/div)

  • 0
    TI__Mastermind 22301 points

    Lasto,

    That's a weird oscillation. 

    The FLT_N signal should not be that far off of VOUT.

    It looks like there some voltage divider to ground involved somewhere else in your circuit.

    Can you try disabling the LM5180(Pull EN low) and put a dummy load to see if the issue is with the TPS2662?

    If it works and the issue is not there, can you provide scope shots of the LM5180 SW and VIN (measured after ferrite bead) ?

    The 14.9V open is expected with your Zener. The 6.5V looks like an input power or current limit.

    Let me know your results,

    -Orlando Murray

  • 0 in reply to Orlando Murray
    Intellectual 600 points

    Thanks Orlando for your prompt reply.

    Attached is the scope shot of the LM5180 VIN (pin3) and SW (pin 1); Please note the scales and added "POS" values of each channel at the bottom of the figure.

    Regarding your comment "It looks like there some voltage divider to ground involved somewhere else in your circuit." I see difference about 200mV between them.

     I'll disconnect LM5180 from TPS26624 and send you the output across a dummy load and send you a scope shot.

    Please let me know if you'd need further information or data.

  • 0 in reply to Lasto Roma
    Intellectual 600 points

    I disconnected the  LM5180 circuit from the TPS2662. Here's the snapshot of the output of TPS2662 with and without a dummy load of 200 Ohm (load repeatedly connected and disconnected) . There are no oscillation. 

    It seems that one of the fault conditions of TPS2662 is occurring for some reason. According to the datasheet, the fault conditions are undervoltage, overvoltage, over load, reverse current and thermal shutdown.

    I'll follow up with the TPS2662 team.

    Thanks for your help.

  • 0 in reply to Lasto Roma
    Intellectual 600 points

    Hello Orlando.

    I replaced the TPS26624 device with a new one and it seems everything is normal now (no shutdowns on startup so far, and output voltage values are correct). It seems that the original device became defective somehow.

    Thanks for your help.