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TPS61183: Waveforms of FSW pin

Part Number: TPS61183

Now our customer is using TPS61183 as backlight driver for 15.6 notebook.

One of the boards could not work.

I have checked, VIN=12V, VOUT=12V, which means, the boost doesn't work. (The right VOUT should be 28V)

I have checked VIN pin, VDDIO pin and EN pin, they are all correct. And the PWMIN is also pulled to high.

And start up waveform is also observed, no switching on SW node, VOUT always follows VIN.

I find the voltage on FSW pin is 0V. (I even turn the scale of scope to 10mV, still very small signal, only some noise)

I think this is abnormal. So could you please provide the right waveforms for this pin? And which block of the chip may be damaged?

Thank you.

Attachment is the schematic.

15.6 FHD Lenovo SCH.pdf