LM4755: LM4755 Mute pin functioning

Hi, Deepak,

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

The mute pin is used to disable both amplifiers. It requires of a minimum voltage of 2V in order to have a correct mute function. A lower voltage won't have any effect. The external transistor drive circuit is optional. You may provide this or another available solution like a microcontroller or any other voltage source to enable or disable the mute function.

Please let me know if you have additional questions or comments on this. We will be glad to help you.

Best regards,
Luis Fernando Rodríguez S.

Thanks,

Just to confirm 

Mute=0V Enable or Disable

What if case if we keep it open?

Input signal gets amplified?

Hi, Deepak,

If Mute = 0V, the amplifier is enabled and the input signal gets amplified.

I wouldn't recommend to leave it floated since there could be risk to have a mute event in case of noise or interference. If this pin won't be used, I recommend to pull it down to GND.

Best regards,
Luis Fernando Rodríguez S.

Thanks Luis.

I have kept it open one of my circuit and wondering why output is not coming.

Will connect to GND and will check.

Do you recommend any of the circuit without microcontoller?

During turn on (Or apply vcc) Mute Pin disable and after some time is Mute disable.

Hi, Deepak,

Please try connecting it to GND and let me know if it works.

If you are not planning to use the Mute function while the device is working, there won't be necessary an external circuit. Just the pull down resistor to GND. However, if you will enable and disable the mute function, you would need of a external control. A voltage controlled switch or a transistor like the typical application example.

Best regards,
Luis Fernando Rodríguez S.

Hey Luis,

Pin2-connected it to GND.

MY SUPPLY IS 24VDC

I have noted voltage keeping DC Bias.

Pin1 (OUTA)-1.2V

PIN2(MUTE)-0V

PIN3 (INPUTA)-2.8V

PIN4 (VCC)-24V

PIN5 (GND)-0V

PIN6 (Bias)-2.8V

i have applied 500mV AC Signal at input and i got output different (Attached below)

Hi, Deepak,

Thank you for the provided information.

Could you also provide your LM4755 schematic portion? This is just to have a better approach to this issue.

What components do you have connected to the output? Which load are you using?

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

At the ouput, i have not connected speaker->it is open now

Schematic portion as requested.

Mute pin connected to gnd after our discussion.

As requested

Hi, Deepak,

Do you have different results if you connect the output load?

In addition, could you try reducing the output capacitor (Co). Could you try with 1uF to 0.1uF?

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

i have not loaded any resistor so speaker is not at the output instead it was open for testing.

I will try with 1uF to 0.1uF only for the testing as have frequency constraints of 300HZ to 8KHZ

Regards,

Deepak

Hi, Deepak,

Please let me know how your tests result.

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

Thanks for reply.

Unfortunately i have given 24V to the Boas pin so seems that it got faulty.

Now i checked with Another 3 fresh ICS but vcc and gnd showing impedance of 9.3k But after giving supply it heat like a hell.

For the above test i am only using VCC AND GND and no other circuit is connected.

Deepak

Hi, Deepak,

Just to confirm, are you powering the bias pin externally? This pin must not be powered up, just connected to an external capacitor. 

Is your circuit damaged only when you connect VCC and GND? Could you verify if there is a short circuit between the LM4755 pins?

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

it was mistakenly from my side

I have another 3 IC which fresh stock but there vcc and GND showing 9.3k impeadance but when it powered up it heats like a hell.

FYI. I AM ONLY CONNECTING VCC AND GND (OTHER CIRCUIT IS NOT IN PICTURE)

I have ordered another 5 pieces so will check on the same.

Deepak

Deepak,

Sorry for many questions. This is to have a better approach to this issue.

Do you just connect VCC and GND for this test? I mean, are not there decoupling caps? Are the rest of the pins floated?

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

i have connected only VCC and GND for the Test (Rest pins are floating and No decoupling caps are there)

Regards,

Deepak

Luis,

Today i got new set of LM4755

Where i have checked Inpedance across VCC and GND (9.3K).

While connecting VCC (Pin4) and GND (Pin5) (Other pins are floating), still it takes around 160mA at 18V and still sucking more current from variable power supply and it heats like hell.

Do i have to do anything extra to avoid this?

Deepak,

Is the heat sink being connected to a thermal pad to GND?

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

Heatsink is not connected.

Regards,

Deepak

Deepak,

Could you try connecting it, please? As mentioned in the datasheet, when more than 16V are used the heatsink is required.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

I have connected in series Multimeter and measured currrent

current is around 160mA at 16V and it keeps taking.

As per graph it is showing less than 20mA.

I will try out Heatsink option and get back to you.

But still could you please check with the customer who are using the same IC for their functioning. 

Luis,

Could you please check with other people using LM4755?

Deepak

Hi Luis,

I have connected Heatsink, but it still taking much current.

I have again made new application circuit as shown in 3rd Post but still it s heating.

Deepak

Hi, Deepak,

I have made some tests on the LM4755 and it is not heating when the power supply is connected. In order to have a better approach to this issue, I would need of your schematic and layout. I need the design files, not a drawing from our datasheets as you have shared. In that way we can see all the connections with clarity and point you to the possible root cause.

Could you provide these files, please?

Thank you in advance.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

i have made schematics as per the datasheet ideal circuit using same components shown in the schematics.

To be more precise, for few IC, i have connected only VCC and GND (Other all pins were open-Not connected to anyone).

Could you please share your schematics?

Regards,

Deepak

Hey Luis,

Half problem solved.

i have shorted pin 7 and 8 (Earlier it was floating) now It is not consuming or heating it is working as per expectations.

One thing i have observed that for the Mute Pin When it was open (Floating) it is amplifying the signal and when Mute pin tied to GND then it was amplifying.

Another thing do we need to generate +5V

From the below table i did not get the VCC additions what is impact.

Hi, Deepak,

You would require of at least 2V to place the device in mute mode.

Regarding the table 1, these recommended R and C values must be placed in order to avoid pop issues. If the mute pin is changed from low to high quickly, there could be a DC level on the inputs and outputs. This DC offset would cause a pop issue.

The RC filter is placed to mute the device slowly, avoiding problems like this. The RC selection depends of the VCC level.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

Thanks for the info.

My questing is here that do i need to convert +5V from the VCC (+24V)?

Regards,

Deepak

Hi Luis,

i did not get the statement written in datasheet.

could you please explain me more better as you have understood my circuit.

I am using Pin1 and Pin 3 (Any one channel from 2).

Hi, Deepak,

Regarding your question about +5V and VCC, there's no need to generate your +5V from VCC supply. The table only describes the recommended R and C values for the different +5V and VCC combinations.

The paragraph that you attached mentions the risks to generate oscillations due to the proximity of the inputs (particularly the non-inverting pins) and outputs. This proximity may result in a positive feedback path. Consequently, it will result in oscillation. In order to avoid this kind of issues, it is recommended to AC-couple the inputs.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis,

Thanks for the explanation.

I have few pins open.

Pin 7-INA

Pin 8-OUTA

Pin 9-NC

Shall i connect 0.1uF (C2,C7) non-polar capacitor and keep it open as in below schematics.

i am using only one channel (INB,OUTB) for my operation.

Regards,

Deepak

Hi, Deepak,

The unused analog input INA (pin 7) must be connected to the 0.1uF capacitor to GND.

OUTA (pin 8) and NC (pin 9) must be left floated. The output capacitor can be removed from OUTA if it is not used.

Best regards,
Luis Fernando Rodríguez S.

Hi Luis.

Thanks for answering my queries.

Could you please help with Mute LOgic.

We have spend much time but yet not conclude on it.

Do you have any simpler solutions?