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# LT3763 gets very hot and breaks

Hi. I have problems with LT3763.

As a DCDC-converter with current limitation, this IC should load large capacities (10mF) up to max.12V.
After switching on the power supply, the IC gets very hot and breaks. Short circuit between Pin26 (SW) and GND.
This also happens without a load at the output.
Supply voltage:  48VDC, Output voltage: 12V, Max output current: 2.77A.

`The IC is switched on via an MCU`

I'v checked all but I have no idea what is wrong.

• Hi MathWest,

Can you double check your chosen MOSFETs? Make sure they are properly rated. Please follow the layout guidelines found on page 22 or copy the demo board layout as close as possible.

• Hi ron.p

I just test new MOSFETs.

As soon as I've finished the test I'll let you know the results.

Thanks a lot for your help.

• Hi ron.p

New MOSFETs are OK.
The circuit behaves as desired.

In my calculation I strictly adhered to the data sheet. That was wrong.
In which cases do you have to follow the redommendation in the data sheet?

Page 14, Data sheet "Switching MOSFET selection"

`"A good approach to MOSFET sizing is to select a high sideMOSFET, then select the low side MOSFET. The trade-off between RDS(ON), QG, QGD and QGS for the high sideMOSFET is shown in the following example. V O is equalto 4V. Comparing two N-channel MOSFETs, with a ratedVDS of 40V and in the same package, but with 8× differentRDS(ON) and 4.5× different QG and QGD:M1: RDS(ON) = 2.3mΩ, QG = 45.5nC,QGS = 13.8nC, QGD = 14.4nC, RG = 1ΩM2: RDS(ON) = 18mΩ, QG = 10nC,QGS = 4.5nC, QGD = 3.1nC, RG = 3.5Ω"`

I think the same MOSFETs with low Qg are a better choice.