LM27762EVM: LM27762

Hi Kumar,

The LM27762 cannot generate exactly +5V and -5V, from a 5V input, at the outputs because of the voltage drop from the LDO and also due to the output impedance of the device. So the actual voltages will be slightly lower. 

Regarding the noise, can you explain how you are measuring this noise and please send waveforms/data which would help explain it.

The LM27762 is a switching converter, so naturally there will be some noise generated at the pins C+ and C-. Please take a look at section 8.2.2.3 to see how the charge-pump works.

Regards,
Davor

Dear 

The generated noise audiable at the same  time output voltage  generate  correctly 

Hi Kumar,

This device has a PFM mode at light load which effectively decreases the fundamental frequency of operation. If your load is quite low, then probably the device is running in PFM mode and the fundamental switching frequency could be in the audible range. However the audible noise usually comes from the ceramic capacitors - not from the IC itself. Here is a nice blog which explains this: https://e2e.ti.com/blogs_/b/powerhouse/posts/how-to-reduce-acoustic-noise-of-mlccs-in-power-applications 

1. At what load is the device operating?
2. Please send a waveform showing the voltage on C+. That way we can see if the converter is running in PFM mode.

Regards,
Davor

When.i provide clean input signal with small ripple voltage no  auditable noise

When I applied input from Lmz36002  then.it create audiable noise

Please.reply.

Hi Kumar,

What is the "clean input signal with small ripple voltage" that you are applying? Is it coming from an external power supply?
Please send waveforms of both input voltage ripples. In any case, the audible noise comes from the capacitors and not the IC itself.

Regards,
Davor

Hi Kumar,

Do you have any updates on this issue?

Regards,
Davor

Hi Kumar,

I will close this thread for now, if there are updates on the issue in the future please feel free to write back.

Thanks,
Davor