WEBENCH® Tools/TLV61046A: TLV61046A with unstable load

When Load is a Resistor 107Hz noise is not exist

HI Hanh:

Please share the waveform of Vout to check the performance. Thank you !

Hi Minqiu,

Thanks for your reply。

Vout of waveform as below (Vin = 2.95V)

Noise of Preamp output as below

Best Regards !

Hanh

When Vin=2.87V or Vin=2.65V noise is not exist

Vout of waveform as below

and the noise as show below

OLED modules may have a built-in DC-DC converter

Best Regards !

Hanh

Hi Hanh:

Is the OLED current continuous? If not, enlarge the Cout can do some help.

In other hand, if it's caused by the PFM of the converter, it will be hard to solve. 

Hi Minqiu

Thanks for your reply

OLED current not continuous.But I don't know is that there is no noise when the Vin voltage is 2.65 Vand 2.87V. I also made a board (3000pcs), so I'm in trouble.  I would appreciate if there is any solution!

I also tried replacing a larger capacitor, but there is still noise.  What is recommend a power supply IC that can be used for OLED?

Best Regards

Hanh

Hi Hanh:

Firstly, I want to check if the noisy is related to the OLED discreate frequency. May you share more details about that? 

Hi Minqiu:

Then I will measure the output waveform and the oscillator pin of tlv61046a with the output load OLed and resistive.  Unfortunately I am currently on Tet holiday, January 5th I will go to work and send waveform to you.

Happy new year 2021

Best Regards!

Hanh

Hi Minqiu,

I have got waveform of TLV61046A SWITCHING PIN 

With OLED LOAD waveform as below

Remove OLED and insert 730ohm resistor the waveform of SWITCHING as below

Best Regards

Hanh

Hi Minqiu、

Additional：I am using TLV61046A for OLED application, input voltage 1.8~3.0V(two alkaline batteries in series) boost to 12V and TPS61071 for Analog circuit boost from batteries to 3.3V

Best Regards

Hanh

Hi Hanh:

Got that! I'll reply with details later. Thanks for your understand!

Hi Hanh:

Sorry for keeping you waiting. 

According to your waveform, I can imaging the loading current. With the constant load, the frequency of TLV61046A is stable, and no audio noisy, right? 

With the OLED, as the feature of the OLED, the loading is instable. It makes the converter keeping enter/exit the PFM.

Have you enlarged the Cout? 

Thank for your reply

I tried 33uF and 470uF、but noise still exist.

By the way, if the load is increased further, the PFM mode will not be entered and the noise will disappear. However, the noise does not disappear even if the OLED and the resistor (730Ω, the output voltage of TLV61046A is about 10.5V) are connected in parallel. Since the Vin of TPS61071 and the Vin of TLV61046A are connected, I think it is probably a problem of TPS61071. The unstable current consumption of the OLED also made the input voltage of the TLV61046A unstable, which made the input voltage of the TPS61071 unstable.As the picture is uploaded TPS61071 line transient reponse, normally it looks like a red line, but if you look at the datasheet of TPS61071, when Vin goes up, Vout goes up a little. I am making a 3.3V analog with an LC filter after the output of TPS61071. Since the input signal is pulled up to 3.3V analog in the amplifier circuit of the operational amplifier, there is a high possibility that noise will enter.

Best regards,

Hanh

Hi minqiu,

With the constant load, the frequency of TLV61046A is stable, and not exist low frequency noise

Thanks and Best Reagrad

Hanh

Hi Hanh:

Yes, the waveform is followed with my analysis. The Noisy is caused by the loading frequency. If there is enough solution size, I would recommend you add an filter to make the load current smooth. Or change the external comments to  reduce the "audible "noisy. Like use soft-port capacitance, integrated inductance.