LM2902KV: Burning in LM2902, could it be a conducted immunity problem?

Hi Willian,

We will need more information to determine possible causes of the burnout. Could you please provide a schematic of the circuit that includes what the inputs are connected to?

Best Regards,

Alex Curtis

The input signal comes from a hall effect current sensor, i.e. it is an isolatedsensor, where the output is 10mV – 500mV.

Hi William,

Thank you for the schematic. What is the nominal value of VCC_TRD_P1? Additionally, is the amplifier supply voltage (+24V_TRD_P1) 24V or 27V?

Best Regards,

Alex Curtis

Hi Alex

VCC_TRD_P1 = 5V

24V_TRD_P1 = 27V

Hi William,

Thanks for the clarification. One other question, what kind of component is "FIL"? And is there any possibility that it might become quickly disconnected or shorted? If so, this might be causing a large current transient into pin 2 (the inverting input of U2A), which could damage the device.

Currently, there isn't anything in the feedback of U2A to limit the current into the amplifier, so I would recommend adding a low value resistor to help protect the inverting input. I recreated your circuit in TINA with the FIL component omitted and added a placeholder resistor:

Also, when comparing the PCB with your schematic, C8 and R3 look identical and have the same package markings, so I just want to confirm whether C3 on your board is a capacitor or a resistor. 

LM2902KV Burn Issue.TSC

Best Regards,

Alex Curtis

Hi Alex.

The component "FIL" is comom mode filter - https://www.we-online.com/components/products/datasheet/744253200.pdf

The chance of the filter opening is almost zero.

Hi Alex.

The component "FIL" is comom mode filter - https://www.we-online.com/components/products/datasheet/744253200.pdf

The chance of the filter opening is almost zero.

Hi William,

Thank you for the additional information.

Although the filter itself may not be opening, if the device connected to the header (CON1) suddenly disconnects, this could cause a spike in current due to the inductance of the common mode filter. Please provide more details about the power up sequence of the board, and if possible, an oscilloscope capture showing the behavior of U2A during operation, including power up.

We're thinking that the inductance of the filter combined with a transient event could be causing an inductive kickback, which is a common cause of damage to ICs.

Best Regards,

Alex Curtis

Thank you Alex,

And could this transient be related to negative voltage?

I did some tests and applied +74V to the IC, and it didn't burn. However, when I quickly applied -10V, it burned.

Hi Willian,

Please elaborate on the tests that you performed. Which pin did you apply the transients to and what was the supply voltage during this test? 

Best Regards,

Alex Curtis

Hi Alex

The negative transient was applied between the power pins. By adding a schottky diode between the pins, the IC was protected from the negative transients.