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TPS61169: Flickering at 70% duty cycle

Part Number: TPS61169

Hi team,

Can you have look at the following customer inquiry please?

In a current project I used the TI TPS61169 to drive a display backlight. The driver worked without problems in the pre-series, but currently we are struggling with a significant flickering of the backlight. The driver is supplied with 5 V and drives a LED backlight with max. 200 mA (@ 9.6 V). I have attached the circuit part (schematic and layout section). The flickering occurs mainly when the dimmingpwm exceeds 70% dutycycle (Freq: 50 KHz), in the darker range below 70% it works. During the transition to series production we adjusted the layout of the mainboard again and changed it in the following areas: Layer structure, buffer capacitors and display cables.

Generally there are slight noise signals on all voltages, probably processor clock/display clock and display data), so also in the feedback branch at pin FB (Rset). I have now tried to filter the noise with small capacitors (470 pF) in parallel to the Rset, which is successful at least on one device. However, I am not sure if I am really at the cause here. My guess is based on the fact that the disturbances on FB cause the controller to briefly detect a supposedly too high current at voltages above 204 mV in the LED branch.

A further consideration, to reduce the Rset to 0.5 Ohm and to control the PWM only up to 50%, was unfortunately not successful.

Thank you,