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LMZ31710: LMZ31710 12V Input, 5V Output. But 12V output and no shot between 12V Input and Output

Ammar Khan
Prodigy 20 points
Part Number: LMZ31710

I have this schematics of LMZ31710. I am supplying 12V input and configured to get 5V output. But I am getting 12V at TP43. Ideally I should be getting 5V. Just to understand. If I measure R2295 and R2297, i should read the exact values? On PCB, right now they are giving values of R2295 = 50kOhm and R2297 = 15 Ohm

Just to let you know, I have 2 PCBs. I am performing test on 1 PCB which I had powered on already. But the other PCB is not powered yet. And both PCBs give same values of resistors.

  • 0
    TI__Guru 50120 points

    Hi Ammar,

    TP43 looks like the output voltage test point. If you measure the resistance between VIN and VOUT, what do you get? It sounds to me that somehow the input voltage (12V) is shorted to the output voltage, which may explain why TP43 is reading 12V. The VADJ pin is not related to the RT/CLK pin so R2295 and R2297 should not be reading the same voltage.

    It looks like you are following the recommended component values listed in Table 2 for 5V ( Rset =0.196kOhms; Rrt = 63.4kOhms, Fsw = 1MHz)

    Have you tried taking a new LMZ31710 device and swapping it with the first board to see if the output voltage is 5V? Please also provide PCB layout for me to review the connections.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Ammar,

    May I get an update on this? Were you able to check the functionality of your board with a new LMZ31710 device?

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Prodigy 20 points

    Sorry, I lost track of this. Yes we found out that LMZ is somehow damaged. Not sure of the reason. We replaced it and it worked fine. There was no short.