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TAS5717 / 3 questions

K.Yaita
Guru 29700 points
Other Parts Discussed in Thread: TAS5717

Hi,

I have 3 questions about TAS5717.

Could you follow me please?

 

(1)ferrite bead for BTL

My customer wants to use ferrite bead for BTL configuration of speaker(output power is about 4W).

Can ferrite bead be used for BTL if inductance value is above 4.7uF?

Are there any precautions?

 

(2)#HP_SD pin for hard mute

In Figure47(P.57), It seems #HP_SD pin could be used for hard mute.

http://www.tij.co.jp/jp/lit/ds/symlink/tas5717.pdf

According to description P.56(below), #HP_SD pin is connected to A_SEL(15kΩ pulldown to ground).

Could #HP_SD be controlled from GPIO(logic level) for hard mute?

---------------------------------------------

Case 2 – Headphone With I2S Input:

Hardware setup: The HP_PWML and HP_PWMR signals should be fed into a low-pass filter (LPF), and the

output of the LPF is fed to analog inputs (HPL_IN and HPR_IN). The A_SEL pin has a 15-kΩ pulldown to ground

and should be routed to headphone amplifier enable (HP_SDZ pin 33).

---------------------------------------------

 

(3)short HPL_OUT and HPR_OUT

My customer think HPL_OUT and HPR_OUT could be shorted if monaural(mono) headphone is connected.

Is this damage TAS5717 in that situation?

 

Regards,

Yaita

  • 0
    TI__Mastermind 34705 points

    Yaita,

    Here are my responses to your questions below:

    1. With ferrite beads we don't recommend using more than 220pF, else you can run into OCP and high idle currents.
    2. HP_SD pin works directly with GPIO in both cases using HP_PWM from device or external analog signal. No need to use ASEL pin configuration unless you're using the HP_PWM and want to use I2C control to shutdown the HP.
    3. If a mono HP is used instead of stereo, the HPR_OUT will be shorted to ground. The short-circuit protection will shutdown/Hi-Z HPR.
  • 0 in reply to Damian Lewis
    Guru 29700 points

    Hi Damian

    I appreciate for your support !

    In question 1, I'm sorry that I couldn't understand why OCP and high idle current occured by using more than 220pF with ferrite beads.

    Is there any technical material about that?(application note etc.)

    Regards,

    Yaita

  • 0 in reply to K.Yaita
    TI__Guru**** 189399 points

    Hi, Yaita-san,

    The ferrite bead doesn't have inductance like the inductor, so if you put too much capacitance after it, it will draw a lot of current as you still have the full pwm waveform across the cap.

    For the inductor, you only have the audio signal across the cap.

    i = c * dv/dt

    -d2

  • 0 in reply to Don Dapkus
    Guru 29700 points

    Hi, Don-san

    Thank you for the explanation.

    I really appreciate!

    Regards,

    Yaita