• State
  • Locked Locked
  • Replies 7 replies
  • Subscribers 63 subscribers
  • Views 544 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.

LM5175: No pulses on HDRV2 in Boost Mode

Thomas Ullrich
Prodigy 40 points
Part Number: LM5175

Hi,

we have several designs built with LM5175 that are working very well. With one of these we got a new lot and have trouble with the free wheeling diode in parallel to the high Driver output FETs. Now I found that the Controller doesn't Output the gate Signal HDRV2  to the high Drivers whereas the LDRV2 is coming.The Output voltage (32V) is stable but all power is fed throug the Diode instead of the Transistors.  I changed the Controller as I suggested that it is defect but it is still the same. The amazing Thing is that it Outputs the Signals when I operate the Booster from a weak (24V) power supply and it stops outputting the Signal running with a strong (24V) supply. This behaviour is Independent of the Output power. We already have produced this board a couple of times running well so the design is working well.  From the new production lot I got the first 4 Units and all have the same behaviour.

What can the reason be that the LM5175 does not output the HDRV2 Signal?

Thanks for your help

Thomas

  • 0
    TI__Mastermind 21720 points
    Hi Thomas,

    Can you please post the schematic? This will help to debug the issue that you are seeing.

    Are you just seeing this on one board? Have you move the same controller to a different board? If so does the same pat show the issue on a different board?

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 40 points

    Hi Garett,

    many thanks for your reply!

    Here is the schematics.

    I changed controllers on these boards but only replaced them with new ones.

    3000050578_05156957.pdf

  • 0 in reply to Thomas Ullrich
    TI__Mastermind 21720 points
    Hi Thomas,

    Thanks for supplying the schematic.

    Also can you please explain what you mean by a weak supply and a strong supply? Is it just the current rating of the supply? Is this independent of input voltage as well? For example is the FET on 100% of the time in buck mode? It might be worth to probe the BOOT2 to SW2 voltage to make sure this voltage is high enough to drive the FETs.

    If you have any waveforms of the HDRV2 to SW2 and LDRV2 to GND signals please send them over.

    -Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 40 points

    Hi Garrett,

    the difference between the two power supplies is: PS1 is a tunable supply with 150W and PS2 is a fixed 24V / 600W power supply. With PS1 I can adjust any voltage bettween 15V and 48V without any problem at any power up to 150W. With PS2 the wrong behaviour exists Independent of the drawn output current. You can see this from the plots. All the plots are the same Setting of the scope. The only difference is the connection to PS1 or PS2. The voltage between SW2 and BOOT2 is in either case around 7V.

    The file names of the plots I uploaded relate to the power supply 1 or 2, the signal name respectively and two types of output power (7W and 55W). Channel 2 is allways tied to SW2, channel 1 displays the respective signal.

  • 0 in reply to Thomas Ullrich
    TI__Mastermind 21720 points
    Hi Tom,

    Thanks for explaining about the difference between the power supplies. Another thought is to check the SS pin voltage in both cases.

    Can you please post the waveforms you talk about?

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 40 points

    Hi Garrett,

    I uploaded the waveforms last time - here it is again - hope it works now.

    On the ss pin I could not see a difference.

    Meanwhile I could overcome the problem by changing values for the slope capacitors. I tried to use this value on the other boards but it did'nt work. In the past we produced severeral boards with the values calculated by the webench and shown in the schematic. The boards work very well. Now it semms to me that we need to vary the value board by board? I changed a lot of devices until the boards were working now. Can it be that we got a bad lot of devices?

    Thanks for your help Garrett.

    Thomas

    HDRV2.zip

  • 0 in reply to Thomas Ullrich
    TI__Mastermind 21720 points
    Thomas,

    Can you please double check the slope capacitor value using the quick-start calculator?
    www.ti.com/.../lm5175quickstart-calc

    Thanks,

    Garrett