Two LTC3388 powered by the same Vin rail: issues occur

I have two LTC3388-3 that are powered by the same Vin rail @12V. Another VR, LT3971-3.3, is also at the same Vin rail. No load is attached to the output of the VRs and my goal is to check the power-efficiency of the VR at this scenario.

If only one LTC3388-3 is powered (any of them), the functionality is okay and the power consumption matches the expected (Iavg <1uA). However, when the second LTC3388-2 is activated, something happens with the overall power consumption and peaks of more than 1mA show up. Nonetheless, the Vout=3.3V (as configured) is stable at both VRs. The issue are the regular current spikes that push the energy consumption to much higher values than expected for this ultra-low power design. Any hints?


C_Vin (for each VR) = 22uF/16V NG0 ceramic

C_CAP_pin3 (for each VR) = 0.47uF/16V NG0 ceramic

C_Vin2_pin7 (for each VR) = 4.7uF/6.3V NG0 ceramic

C_Vout_pin6 (for each VR) = 22uF/6.3V NG0 ceramic

L (for each VR) = 22uH, LPS5030-223MRC shielded power inductor



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