ROHM FAQ

FAQ's
  • For Portable Speaker Amplifiers,
    How is the output LC filter constant for a Class D Speaker Amplifiers determined?
    • Since the characteristics of the LC filter vary not only with the LC constant but also with the speaker load resistance, the optimum LC constant depends on the load resistance value.
      For ROHM's portable Class-D Speaker Amplifier, L=22µH and C=0.47µF are recommended for 8Ω load resistance, and L=10µH and C=1.0µF for 4Ω load resistance.
      When changing from these constants, it is recommended that the following conditions are met:
       The fc of the LPF composed of LCR must be sufficiently lower than 1/2 of the PWM Carrier Frequency.
       The Resonant Frequency of the LC circuit must not be within the range of 1/2 to 3 times the PWM Carrier Frequency.
       The Q value of the filter must be less than 1.1.
    • Products: Portable Amplifiers