Tool/software:
I am using LMR38010 in inverted buck boost topology to generate a -70V output from a 5V input. To my understanding this is equivalent to a 75V input and 70V output, and I use this voltage range as the input parameters in Webench Power Designer. In datasheet, LMR38010 accepts 80V max input voltage and may output 75V max. So the settings are with in the specification. Followings are the schematic (KiCAD), PCB layout snapshot (4 layer board with inner layer 1 full copper plane as ground), and webench power design report.
I want ot understand why there is no output. VEE is measured at -0.01V. Hope somebody can tell me where is the mistake. Or, it is beyond the range in of the chip used in inverted buck-boost topology.
I will change the feedback resistor later to see if lower output voltage possibly works. This circuit is used to provide a negative voltage to a high voltage analog switch IC. The power consumption will be very low. Just around a few mA at most. I just need the voltage. Beside 5V, I also have 12V and 70V on board. I choose LMR38010 for its simplicity and relatively few external components. I appreciate any recommendations to replace LMR38010 for -70V generation, if the chip won't do.
