LM4755: LM4755-Unused pin suggestions

Deepak C

Intellectual 360 points

Part Number: LM4755

Hello Sir,

I have prepared Prototype for the LM4755 as attached below circuit.

Input conditions:

VDD=22VDC

INPUT SIGNAL:200mV (1KHZ).

Output yet not connected.

Here, problem is that

IC LM4755 is getting heat up when we powered up with 24V

Could you please let me know about the pins connections in above circuit.

INA Pin connect to?

OUTA Pin Connect to?

i have checked with following combinations

INA=GND,OUTA=OPEN ,Result: IC Heat up
INA=GND Via 0.1uF,OUTA=OPEN -IC Heat up
INA=OUTA=GND=IC Heat up.
INA=OUTA=BIAS Pin-No Heat up, but Bias pin voltage reduce to 1.5V (Instead of Half VDD) and output clipping.

I did not get the Any statement in the Datasheet?

Regards,

Deepak

over 4 years ago

0 Luis Fernando Rodriguez S. over 4 years ago

TI__Guru* 84915 points

Hi, Deepak,

Thank you for the details on this issue.

When the analog inputs are not used in the audio amplifiers, they should be connected to GND through a 0.1uF capacitor.

The analog outputs should be left floated when they are not used. However, I noticed that you have an issue in this case. Have you tried to disconnect the snubber array (C5 and R2)? Do you have the same results?

Any information you have, please let us know.

Best regards,
Luis Fernando Rodríguez S.

0 Deepak C over 4 years ago in reply to Luis Fernando Rodriguez S.

Intellectual 360 points

Hi Luis,

Today, i have built another prototype and checked removing C5 AND R2.

Problem is still with the IC Heating.

Regards,

Deepak

0 Luis Fernando Rodriguez S. over 4 years ago in reply to Deepak C

TI__Guru* 84915 points

Hi, Deepak,

Thank you for your feedback on this. I have some other questions for this issue.

Have you tried with more units on this? I mean, have you replaced the LM4755 with other samples and do you have the same issue?

Could you try with a different power supply and see how it results?

Do you have the same issue if you connect the load to the amplifier B?

Is the device protected when the temperature increases? How much current is demanded to the power supply when this issue appears?

Best regards,
Luis Fernando Rodríguez S.

0 Luis Fernando Rodriguez S. over 4 years ago in reply to Luis Fernando Rodriguez S.

TI__Guru* 84915 points

Hi, Deepak,

Excuse me, do you have a feedback on this?

Thank you.

Best regards,
Luis Fernando Rodríguez S.

0 Luis Fernando Rodriguez S. over 4 years ago in reply to Luis Fernando Rodriguez S.

TI__Guru* 84915 points

Hi, Deepak,

I'm closing this E2E thread for now. But please let me know if you have additional observations or comments on this. We will be glad to help you.

Best regards,
Luis Fernando Rodríguez S.

0 Deepak C over 4 years ago in reply to Luis Fernando Rodriguez S.

Intellectual 360 points

Hi Luis,

My prototype ran now.

Only thing we were missing is that we have to connect unused out pin with snubber (2.7R+0.1uF to gnd).

Regards,

Deepak

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LM4755: LM4755-Unused pin suggestions