LMR33620-Q1: Output Voltage Instability

Ashley Neurauter

Part Number: LMR33620-Q1
Other Parts Discussed in Thread: LMR36502, LMR36501

Tool/software:

Hello,

After configuring a design based on a WEBENCH output to use the LMR33620CQ3RNXTQ1, including all passive component values recommended by WEBENCH, I am seeing a very large amount of instability on the output. In the image below, there is a large peak to peak spike seen that exceeded 400mV, as well as a fair amount of ringing. Given that I need to calibrate an ADC with a very stable reference, this is too much variation. How am I able to make this better, by reducing the ringing and the peak-to-peak voltage? Is there an alternate design or chip that would result in less than 30 mV peak to peak?

6 months ago

0 Ridge Lahti 6 months ago

TI__Genius 16220 points

Hello,

Please share the design schematic and operating conditions including Vin, Vout, Iout, Fsw. If possible, please also share the Webench link.

Best regards,

Ridge

0 Ashley Neurauter 6 months ago in reply to Ridge Lahti

Prodigy 10 points

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=65BDBF26FE654924

please note 3.3uH inductor is shown below due to experimenting with the value, both 1.8 and 3.3 were tested with 1.8 being the trace shown previously and the better of the two.

Vin 15 V

Vout 3.3 V

I out 60 mA nominal, 90 mA anticipated max

0 Ridge Lahti 6 months ago in reply to Ashley Neurauter

TI__Genius 16220 points

Hello,

If those are the maximum expected currents, I think the LMR36502 or the LMR36501 would be better options for the lighter loads.

https://www.ti.com/product/LMR36501

https://www.ti.com/product/LMR36502

Otherwise, you could increase the output capacitance to help with the voltage ripple. Also, when taking voltage ripple measurements, make sure that you are using the tip and barrel method directly over the output capacitor to minimize the loop created by the GND lead of the probe. See the image for reference:

The long GND will couple noise into your measurement which can make the output ripple look worse than it truly is.

Best regards,

Ridge

0 Ashley Neurauter 6 months ago in reply to Ridge Lahti

Prodigy 10 points

Thank you, we will try one of those

0 Ridge Lahti 6 months ago in reply to Ashley Neurauter

TI__Genius 16220 points

Hello,

Let us know if the issue persists. For now, I will close this thread. If you have more questions you can re-open this thread by replying.

Best regards,

Ridge

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LMR33620-Q1: Output Voltage Instability