LV2832Y3DDCR 3V3 regulator output have oscillaction when power loss.

user4869703

Hi TI:

I have a question about LV2832Y3DD regulator.

when 3V3 regulator output turn off, 3V3 would oscillation then turn off. that's oscillation is follow input voltage waveform.

if i change to external DC source but the symptom still there.

Please refer tp the attachment.

LV2832 3V3 output oscillation.docx

Thanks.

over 5 years ago

0 Timothy Hegarty over 5 years ago

TI__Guru 59227 points

Hi user4869703,

Looks like your input supply flattens or slightly increases when it becomes unloaded, resulting in the converter restarting. What are the values of series resistors R325 and R326?

Note that the SHDN waveform (Ch4) shows the voltage increasing at each turn-off. What are the values for the SHDN resistor divider and capacitor?

Regards,
Tim

0 user4869703 over 5 years ago in reply to Timothy Hegarty

Prodigy 220 points

Hi Tim:

The value of series resistors R325 and R326 is 1R / 2R.

SHDN resistor divider R971 and R912 is 100K/ 27K, capacitor value is 0.1uF.

I try to remove the capacior, but the result is the same.

Also,change the ratio of SHDN resistor divider and make UVLO point higher.

With higher UVLO point ,the voltage oscillation can disappear. but the UVLO point too close to the system UV point (10.4 V or higher)

It will result in unexpected trigger when doing some transient test.

Thanks a lot.

0 Timothy Hegarty over 5 years ago in reply to user4869703

TI__Guru 59227 points

Thanks for the reply. The input impedance of the supply is too high relative to the 430mV UVLO hysteresis of the input voltage. Please probe the VIN pin voltage to verify where turn on and turn off occur - the UVLO thresholds are 2.73V on and 2.3V off. The IC's EN pin is not a precision enable function - the EC table specifies turn off at a max of 0.4V and turn on at 1.8V min.

Check out these links for more inforamtion:
www.ti.com/.../slva769a.pdf
e2e.ti.com/.../understanding-undervoltage-lockout

Regards,
Tim

0 user4869703 over 5 years ago in reply to Timothy Hegarty

Prodigy 220 points

Hi Tim:
The input impedance you mentioned is too high and make UVLO voltage immediately increase when input current drops(trigger UVLO and device turn off).
Do you have recommened value of input impedance ?

thanks.

0 Timothy Hegarty over 5 years ago in reply to user4869703

TI__Guru 59227 points

Can you set R325 and R326 series resistors to zero Ohms? That will certainly help.

0 Katelyn Wiggenhorn over 5 years ago in reply to Timothy Hegarty

TI__Genius 11040 points

Hello,

I want to follow up with you on this thread. Were you able to change the resistors to zero Ohms?

Best Regards,
Katelyn

0 Katelyn Wiggenhorn over 5 years ago in reply to Katelyn Wiggenhorn

TI__Genius 11040 points

Hello,

Due to inactivity, I am going to close this thread. Pleas open a new thread if you have any remaining questions.

Best Regards,
Katelyn

0 user4869703 over 5 years ago in reply to Katelyn Wiggenhorn

Prodigy 220 points

Hi Katelyn:

I will going to change to zero ohm with brand new unit.

The experiment will complete within this week.

Thank you.

0 Katelyn Wiggenhorn over 5 years ago in reply to user4869703

TI__Genius 11040 points

Hello,

Thank you for your confirmation. Please let me know if this raises any additional questions.

Best Regards,
Katelyn

0 user4869703 over 5 years ago in reply to Katelyn Wiggenhorn

Prodigy 220 points

Hi Katelyn:
The issue can be solved by change R325 value to 0.5 ohm, i will find tune a appropriate value for final.
Thanks TI support!

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LV2832Y3DDCR 3V3 regulator output have oscillaction when power loss.