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BQ24650: 600kHz noise on output line

Colin Bishop
Prodigy 20 points
Part Number: BQ24650

I'm noticing the output line of my BQ24650 charger circuit has 600kHz noise of around 500mVpp. These look to me like transients as the Hi-side fet opens up, and I am aware that the internal PWM operates at 600kHz. Is this standard operation for the device or are these artefacts suggestive of a circuit error somewhere? 

  • 0
    TI__Mastermind 24075 points

    Hi Colin,

       This is an issue with your layout. Most likely you have your VFB sense line, routed right under or too close to the high frequency switching loop (which consists of your switching FETs, external capacitance closet to drain of high side FET) or right under the inductor, without proper shielding between the layers. This is causing noise (in this case it would be from the internal switching frequency) to couple on to your sense line. Lack of shielding could especially be there if you are using a 2 layer board, so more care would be required when routing your traces.

  • 0 in reply to Kedar Manishankar
    Prodigy 20 points

    Alright. Back to the drawing board.

    Thanks for the insight