TPS61196: TPS61196 IC is failing

Hi Vamsi,

Could you please upload your schematic for me to double check? You could send me the schematic by "request friendship" if you have confidential concern.

BR

Patrick

BACKLIGHT.pdf

Dear Patrick Yao,

Please find the attached schematic.

Hi Vamsi,

Have you measured the fault pin voltage?

And I didn't find the R1, R2, R3 in your schematic, could you please help to indicate them in your schematic as well? Thanks

BR

Patrick

Yes, we measured fault pin also it is always high.

comparing to the datasheet section 8.2  to the attached schematic

section 8.2 of datasheet         attached our schematic

         R1                             -->           R217                                

        R2                              --->          R216

         R3                             --->          R271,R272

        R5                             ----->        R201

After analyzing the failure ICs we understand that some of the IFB pins are showing short to GND or resistance in kohm comparing to the working IC which is coming around 6Mohm. Please let us know what is the reason for failing the IFB pins.

Hi Vamsi,

What is the total output capacitance? And have you captured any waveforms during the test?

Have you soldered the R240, R253, R259, R261, R264 and R273 on your PCB board?

BR

Patrick

We have kept 100uF/200V at the output. Also soldered R240, R253, R259, R261, R264 and R273 with 10ME resistor.

Hi Vamsi,

I will give you feedback once back to office.

BR

Patrick

Hi Vamsi,

Have you captured any waveforms during the test? Like SW voltage, inductor current, LED voltage and current......

How many ICs have you tested and will every IC be damaged?

BR

Patrick

Hi Patrick,

what is SW Voltage?  We are assuming GDRV pin voltage. Below is the wave form for the inductor current waveform and GDRV pin voltage. we have connected a current sensor series to inductor to

measure the inductor current and sensor output is 200mV/A.

Hi Vamsi,

SW is the switching node, which you could capture the Drain voltage of the MOSFET.

BR

Patrick

Hi Patrick,

Attached  the captured waveform

Ch3 - inductor current (200mV/A)
Ch2 - led channel voltage
Ch4 - SW voltage(drain voltage)

Inductor current(200mV/A)

Hi Vamsi,

Per talked yesterday, please measure the voltage on IFB pins when power on the device.

BR

Patrick

please find the wave form on IFB pins. It is coming around 20V.

we have changed the value of 10Mohm to 100K and the voltage is coming around 15V.

But will this cause for the failure of IFB channels?

Hi Vamsi,

Was this waveform captured when power on the device? Looks like it was in normal operation.

BR

Patrick

Hi Patrick,

After the detailed testing below is the identification for different resistors across IFB to GND

With 100KΩ we have verified for so many power cycles, IC is not failing. Hope this is the solution. We will further continue this testing in some more boards and let you know any failure is happening.

Hi Vamsi,

OK, let me know if you have any update.

BR

Patrick

Hi Patrick,

After changing 100k at IFB pins also one case of failure is observed. Is there any option to add Zener diode across IFBx pins. Please suggest.

Hi Vamsi,

Was this damage still occurred when powering on the IC?

BR

Patrick

Hi Patrick,

Display is powered ON with this IC and working normally for the first day. At EOD we switched OFF the display. Next day morning we powered ON the display it is not working. We dont have any clue why the IC is failed. After replacing with new IC, display is working normally.

Hi Vamsi,

Could you please also measure the voltage of IFBx when power off the device? Just like the measurement you did when power on.

BR

Patrick

Hi Patrick,

We measured IFBx voltage when the unit is powered OFF. But we didnot see any abnormality. Voltage is getting down.

Hi Vamsi,

Was the previous 32.4V @100kohm measured with oscilloscope? Have you observed if there will randomly occur any voltage spike?

BR

Patrick

could you suggest any other need to be verified for the failure

Hi Vamsi,

I think the most possibility is the voltage spike when power on the device, so that's why I want to confirm how did you measure the 32.4V when 100kohm resistor added. Use oscilloscope's trigger to confirm whether there will be voltage spike over 40V is recommended.

BR

Patrick