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LT8619 fails with input short for input voltage higher than round about 18V

Category: Hardware
Product Number: LT8619

Hi, 
I have a new design with the LT8619 to be used as 28..32V Input to regulated 5V output.

I addded a LED with 10mA load current for optical "OK" inspection, no further load applied currently. With 15VDC input voltage from a laboratory power supply, the output is regulated to 5V as expected. With increasing the input voltage above round about 18V, the input is shorted to GND permanently by LT8619. As input voltage range is up to 60V, I did not expect any issues.

I also did a LTSpice simulation with the model provided for the choke (L2) by Wuerth Electronics

int_Voltage_PowerStage.asc

I would assume either spikes generated by switiching effects overcurrent at the power output to kill the IC. Based on the block diagram in the data sheet, a short in the output stage should be detectable by a resistance measurement of pin "SW" to GND / VIN. Both readings are more than 10kOhm (measured with DMM), while the resistance at Pin VIN is less than few Ohms. I also removed the LT8619 from the PCB to cross-check the IC to be the root cause. A direct reading on the removed IC gives also few Ohms between VIN and GND. 

All devices shown in the schematic are placed near to each other within 20mm x 9mm area, same PCB side with short routings.

Did I missed something in the schematics? Is the chosen choke not matching the IC (even with simulation running w/o issues)

Thanks for any support

  • Hi,
    meanwhile I think I may have run into the ringing issue mentioned in the datasheet with my design, as I had not added any electrolyte capacitor at the input. additionally I had yesterday some regulation issues with the ADP2301, which could be fixed by an additional capacitor Unfortunately my scope was at calibration when I switched the design on first time. To do some measurements my issues is now to get additional LT8619 for further investigations. While the LT8619EDD was listed at different suppliers as "on stock" when I designed the circuit, there is nowadays no stock anymore :-|

  • I hope you are good now with your design. Correct to have certain capacitance at the input to absorb the energy of voltage spikes. You also may want to be careful with inductance at the input line either by PCB trace or length of wire towards the DC source. Large spikes at VIN can be generated because of line inductance when you have large capacitor at the input during fast turn-on of input supply.