LM70880: LM70880 stability issue

Hello Helmuth 

You can simulate your design using PSPICE. The model is available at   https://www.ti.com/lit/zip/snvmcd7 

To check stability, you can use Power Stage Designer https://www.ti.com/tool/POWERSTAGE-DESIGNER and select CMC Inverting Buck-Boost as a control scheme. 

Also please refer the Buck Boost section of this article. /cfs-file/__key/communityserver-discussions-components-files/196/0412.slup340.pdf 

-EL 

Hello EricLee

Thank you for your answers. Unfortunately, the simulation model is only partially helpful in this case, as it cannot be used for inverting regulators. The binary model has an internal connection to GND.

The article is very good, but it seems that my problem is not related to stability in general, but rather to the specific regulator.

It turns out that the LM70880 in my application goes to PFM mode instead of CCM. As I set the PFM / SYNCIN pin correctly to AGND/-Vout, I have no idea why this happens. With a 12 V supply, switching from DCM to CCM works, although I want to start and stay with CCM. However, with a 24 V supply, it appears that the regulator remains in DCM mode, which is why the output voltage is unstable for higher loads. What could cause this behaviour?

I found a TI reference design for using the LM70880 as an inverting regulator for -7 to -11 V, so I have a new question: is -15 V also possible? PMP31291 reference design | TI.com

Kind regards,

Helmuth