LM4865: Volume control

Daisuke Higa

Part Number: LM4865

Hi support team.

I have received the following inquiries from my customer regarding volume control issues. Would you please help me to solve it?

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As shown in pattern (1) below, an abnormality has occurred when the IC is started up from the active state, and no abnormality has occurred when starting up from shutdown as shown in pattern (2).

In addition, there seems to be some variation depending on the IC, and there are cases where no abnormality occurs even if the same operation is performed.

As a countermeasure according to the result of pattern (2), we are considering incorporating DC Vol = 0V (IC shutdown) of the IC into the startup sequence as shown in the figure below. Is this okay?

Is it possible to control the volume with this measure?

Best regards,

Higa

over 3 years ago

0 Ivan Salazar over 3 years ago

TI__Guru** 102045 points

Hi Higa,

Could you please confirm on the below for better understanding?

If DC_VOL/SDz pin is different than GND during power up, volume control is not operational
if DC_VOL/SDz pin is GND during power up, volume control is operational

I think the proposed fix for the power up sequence is OK. Most likely this could be related to some internal reference that is not setting up correctly if the pin is not at GND initially.

Best regards,
-Ivan Salazar
Applications Engineer

0 Daisuke Higa over 3 years ago in reply to Ivan Salazar

Genius 3805 points

Hi Salazar-san

Thank you for your prompt reply.

I have an additional question.

Is it okay to make a sudden change from GND to VDD at the Vol / SD input?
I'm worried about the E2E post below.

https://e2e.ti.com/support/audio-group/audio/f/audio-forum/1008705/lm4865-dc-vol-sd-pin-behavior

Best regards,

Higa

0 Ivan Salazar over 3 years ago in reply to Daisuke Higa

TI__Guru** 102045 points

Higa,

I assume the pin would not be controlled by some slider or potentiometer but some switch instead? Unfortunately there is not much details we can get on these old LM devices as the design may be unreachable. I would not recommend operation like that unless you can test several devices to make sure operation is OK.

Best regards,
-Ivan Salazar
Applications Engineer

+1 Daisuke Higa over 3 years ago in reply to Ivan Salazar

Genius 3805 points

Hi Salazar-san

Thank you for your conforming.

I understand.

Regards,

Higa

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LM4865: Volume control