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?

Details:

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

D0=gnd

D1=Vin2

Parents
  • Vouts are unloaded all the time, except when I plug the scope to monitor the outputs. However, even if the scope is not plugged, the issue occurs.

    With the current sourcemeter setup, I cannot monitor the input current of each VR, individually. I would have to out a sense-resistor in series with one of the VRs to get such measurement.

    The setup is simple and by attaching components at the SOT23-DIP6 board. I double-checked all connections for inversions/shorts/opens and they are okay in both boards. Moreover, when the third VR (different model: LT3971-3.3) is sharing the same Vin rail, the issues do not occur with a single LTC3388-3. The problem only occurs when both LTC3388-3 are active at the same time. In certain periods of time (couple of seconds), the issue does not show up and the power consumption matches the expected value for two LTC3388-3 with very light loads. Therefore, I believe that the problem can be associated with a cross-interference between two LTC3388-3 that are very close to each other. What is the switching frequency range for this chip?

    Regards,

    Agnelo

Reply
  • Vouts are unloaded all the time, except when I plug the scope to monitor the outputs. However, even if the scope is not plugged, the issue occurs.

    With the current sourcemeter setup, I cannot monitor the input current of each VR, individually. I would have to out a sense-resistor in series with one of the VRs to get such measurement.

    The setup is simple and by attaching components at the SOT23-DIP6 board. I double-checked all connections for inversions/shorts/opens and they are okay in both boards. Moreover, when the third VR (different model: LT3971-3.3) is sharing the same Vin rail, the issues do not occur with a single LTC3388-3. The problem only occurs when both LTC3388-3 are active at the same time. In certain periods of time (couple of seconds), the issue does not show up and the power consumption matches the expected value for two LTC3388-3 with very light loads. Therefore, I believe that the problem can be associated with a cross-interference between two LTC3388-3 that are very close to each other. What is the switching frequency range for this chip?

    Regards,

    Agnelo

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