Line drive on TDF8546

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Line drive on TDF8546

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mingzhewei
Contributor I

Hello Expert,

What is Line Drive of TDF8546? what's the purpose for this mode? Is it related to Stat-stop function?

How can I know the mid-tap voltage in terms of different Vpp?

I see"Line driver mode supports engine start at a battery voltage as low as 6 V (16 dB and mid-tap voltage 0.25 VP)" on datasheet.

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2 Replies

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TomasVaverka
NXP TechSupport
NXP TechSupport

Hello Minghze,

In case at the output of the amplifier there are not loudspeaker connected, it is a input of an external amplifier. The impedance of the load is changed from 4 Ohm to 200Ohm, you do not need the gain anymore, there in this mode the gain will be reduced from 26dB to 16dB. (Advantage to reduce the noise level for the next amplifier).

The start stop has nothing to do, beside the operation voltage down to 6V also in this mode.

 

Regarding the question: "How can I know the mid-tap voltage in terms of different Vpp"

 

- Basically, in the line driver mode the midtap level at the outputs will be approximately Vp/4 down to a supply voltage of approx. 10V. Below 10V the behavior changes.

- We will create a graph to show the behavior. 

Best regards,

Tomas

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jason_chen2
Contributor I

Hello Tomas:

Could I ask more question about line driver?

1. The gain of Line driver mode and low gain mode are both 16db. 

    (1) If we need to drve a separate amplifier or booster, could we select low gain mode?

    (2) If we only can select line drive mode, what advantage of line driver mode than low gain mode?

2. In page 26 of datasheet , Could you help to explain it in more detail for below contens? Why the drives the input stage of the booster below the ground level?

(If the DC output voltage is set to half the battery voltage, with an engine start the common mode voltage will change quickly from 7 V to 3 V. This drives the input stage of the booster below the ground level.)

Best Regards,

Jason

2020.03.27

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