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LTM8024 won't start

Category: Hardware
Product Number: LTM8024

I have two LTM8024 umodules in my design. One of them is configured with both outputs in parallel and the other is a third parallel of the first rail and also a second rail. The two rails are 3.3v and 1.15v. The 3.3v is supposed to come up first then the pgood triggers a delay circuit which then enables the 1.15V rail. The share pins are connected per the datasheet. The feedback pins are connected per the datasheet with properly selected resistor values. Each of the TRSS pins has a 0.01u cap on it, which should be reasonable. The run pins for the three parallel legs of the 3.3v are tied to a circuit that properly send a 5V level to turn the supplies on, but they don't turn on. When the run signal goes high, the TRSS1 pin rises to 2V in about 20ms, the TRSS2 pin never rises above 0V. Has anyone seen this issue before?

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  • I have removed the capacitor on the TRSS2 pin and there is no change. I also removed the capacitors on all the TRSS pins, again no change.  

  • Hi ,

    Thanks. Without seeing the actual circuit it is hard to say what is wrong. As you are using 3 paralleled and one separate outputs, there is no exact circuit example on the datasheet, thus it would be informative to provide your circuit schematics.

    What is the input voltage?

    As the chip comes in BGA package, it is sometimes possible that there is a poor solder joint. However, as you are seeing the same problem in several boards, that is unlikely. Re-check that all symbol pins are correctly mapped to the geometry.

    cheers, heke