LM4990: Please help us with the review of the LM4990LD/NOPB audio amplifier design.

Hi, Sijutha,

Welcome to E2E and thank you for your interest in our products!

Have you tried connecting the PAD (pin 11) to GND? In addition, could you try routing the BYPASS pin to IN+ directly? I mean, could you remove the resistor R111, please?

Also, do you have details about the output? I mean, when you power up the device, do you see any voltage level? What happens when you use an input signal (let's say a 1V sine wave signal)? What do you see at the output?

Any other information you could provide will be appreciated.

Best regards,
Luis Fernando Rodríguez S.

Hey,

Sorry for the late reply.

I have been working on the amplifier section. I have given audio out signal from the SBC ( 0.017 V across AUDIO_OUT_L & AUDIO_OUT_R) ,and obtained 2.136V in connector J12(across VO1 & GND)  and 1.36V in connector J11(across VO2 & GND).

Whereas no sound is generated from the speaker. I have done all reworks as you said in the previous mail.

Kindly help us to get the output as earliest.

Schematic is attached for reference

Hi, Sujitha,

Are you connecting the speaker in single-ended or differential configuration? Could you try with a single 1KHz sine wave tone at the IN- input and see how the output reacts? Have you tried with different LM4990 samples?

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Hi,

I have been connected the speaker in the  single ended and differential configuration. Now, we are working in differential configuration, and observed that,  there should always a  voltage of 1.75 V across the output pins of the LM4990(even when there is no input, there should be a output voltage).

Also, provided 1KHZ sine wave tone to the input of the amplifier , and no variation in output obtained.

We have been tested different boards.

Is there any shutdown, SD pin configuration required for the proper output.

Regards

Sujitha S