TAS5782M: TAS5782M's minimum recommended Lout

hello, Inductor selection is decided by Switching frequency. Please read through below docs to understand L, C selection guidance.

www.ti.com/.../slaa701a.pdf

regards
Linda

Hello Linda,

I would like to know about why minimum inductor value was limited and whether this minimum value consider about the tolerance of inductor.
It is not how to select output inductor.

Could you give your answer for my question?

Best regards.
Kazuki Kuramochi

Hello Linda,

Would you answer my question?
I'm looking forward hearing back from you.

Best regards,
Kazuki Kuramochi

Hello,

One the one hand, PWM switching frequency Fsw=384KHz, LC filter need to provide enough attenuation for Fsw. Hence, L cannot be too small.
On the other hand, TAS5782 is a closed loop amplifier, which indicates that it has its own loop bandwidth. Based on our evaluation, bandwidth <~100KHz are recommended.

Hence, usually, I would recommend to use the inductor as we suggested in datasheet and EVM board. On my side, larger than 4.7uH is recommended.

Regards,
Alix Wan

Hello Alix ,

Thank you for your answer.
I have additional question for your answer.

If we just consider about cut off frequency, there is no problem regarding choosing too small inductor. This is because, LC filter's cutoff frequency is determined by inductor and capacitor. Thus there is no problem regarding cutoff freq if we chose to large capacitor.
But if we choose too small inductor, it occur large switching current ripple. I guess this ripple occur OCP so you defined minimum recommended inductor value on datasheet. Is this correct? Moreover if your concerned about output current ripple, this recommend value is no difference between BTL and PBTL, right?

By the way, dose this recommended value has the margin for coil's inductance tolerance? For example, Recommend value is 1uF, however we have 20% margin.

Best Regards,
Kazuki Kuramochi

Hello Alix,

Would you provide your opinion for this?

Best regards,
Kazuki Kuramochi

Hi,

Would you give me any feedback for my opinion?

Regards,
Kazuki Kuramochi

Two considerations when selecting components of low-pass filter :1. it is the cutoff frequency 2. Q factor or damping ratio. there is corresponding calculator parameter in last link: www.ti.com/.../slaa701a.pdf
besides those two factors, we also need to consider inductor Isat (vs temp, power) and LC selection also could impact ripple current on inductor (more current consumption).
for inductor selection, mostly make sure when drive max power , inductor value drop still can tolerate I peak.

regards
Linda

I understood about what points we need to consider when we design output LC filter.

I would like to confirm about below things.
Why did you list the recommended minimum inductor and how do you calculate this value? Moreover Why did you describe it as a short circuit condition only?

Regards,
Kazuki Kuramochi

HI Linda,

Is this minimum inductor value recommendation able to apply the both of BTL and PBTL? or each operation has different recommendation?

Best regards,
Kazuki Kuramochi