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BQ24157: BQ24157

Yan Pui Chan
Intellectual 510 points
Part Number: BQ24157

Hi,

We have one product that uses the TI charging IC – BQ2415YYFFR and having issues with passing the EMI (RE) certification test.

We tested different configurations and found that moving the RC filter (C5 and R5) before the inductor helps. *See the below picture for reference.

Questions:-

  1. Do you see any issues with moving C5 and R5 before the inductor (L1)?
  2. For the RC circuit (C5 and R5), do you have any recommended values?
  3. Are the RC circuit (C5 and R5) having max values that cannot be exceeded?
  4. Please also let me know if you have any other recommendations for us to improve the EMI-related issues.

  • +1
    TI__Mastermind 29700 points

    Hello, 

    Thank you for reaching out via E2E. For EMI suppression yes it is recommended to have an RC filter at the switch node (i.e. before the inductor).

    2/3) Please start with R = 1ohm and C = 15 nF as reference, but TI recommends to try several different combinations to get best results with your custom PCB design. You will want the capacitance in the RC filter to be approx. 1 to 3 times the parasitic capacitance of the output path of the charger IC. 

    There is no strict max value, but be aware there is a tradeoff between EMI improvement and efficiency reduction when RC values become larger. 

    4)Another recommendation is to add a 1 nF capacitor at PMID, SYS, VBUS (optional), and BAT (optional). The purpose is to add this high frequency cap which works in 100MHz to 200MHz range to return high frequency noise to GND. 

    Best Regards,

    Garrett