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can not shutdown output from LTM4622 by pin RUN

Category: Hardware
Product Number: LTM4622EV#PBF

Hello all, 

We have a issue with LTM4622. The output of 3.3V in the following schematic will have 1.1V level even the RUN2 is off. The output of V_1V2D is 0V when RUN1 is low.  

This 'leaking' voltage on V_3V3D will cause problem, because the  'leaking' voltage' mess up other IC's power sequence requirement.

 The RUN1 and RUN2 are pull down to 0.05V level in my PCB, and the V_SYS_D is 12V. 

Any suggestion will be appreciated. 

Thanks in advanced. 



typo
[edited by: hyphen at 11:48 PM (GMT -4) on 29 Jun 2022]
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  • Hi hyphen,

    Do you have a load connected to your output? It could be that the output capacitors are not yet fully discharged that's why you are still seeing a voltage output.

  • thanks, ron.p, for your input. 

    Actually, I already put a constant load for the output of 3.3V, 150ohm. still have the voltage forever. 

    I change the mode to burst, and operation frequency to 2Mhz, but still there is 0.46V 'leaking' voltage' on the 3.3V output when RUN is off.

    I have one LTM4622 (1.2V and 3.3V) and one LTM4622a (5V and 5.5V) on my PCB; the LTM4622 has 0.46V on 3.3V, and 0V on 1.2 output; while the the LTM4622 shows 2.5V on 5.5V output and 0V on 5.0V.

    strangely, the problem outputs are both the output2, i.e. the higher voltage output in either LTM4622 and LTM4622a circuits.

    Would you think this details be of some clue?   

     

Reply
  • thanks, ron.p, for your input. 

    Actually, I already put a constant load for the output of 3.3V, 150ohm. still have the voltage forever. 

    I change the mode to burst, and operation frequency to 2Mhz, but still there is 0.46V 'leaking' voltage' on the 3.3V output when RUN is off.

    I have one LTM4622 (1.2V and 3.3V) and one LTM4622a (5V and 5.5V) on my PCB; the LTM4622 has 0.46V on 3.3V, and 0V on 1.2 output; while the the LTM4622 shows 2.5V on 5.5V output and 0V on 5.0V.

    strangely, the problem outputs are both the output2, i.e. the higher voltage output in either LTM4622 and LTM4622a circuits.

    Would you think this details be of some clue?   

     

Children
  • Hi hyphen,

    In a standard application for the LTM4622, both Vout's should decay to 0V when RUN1/2 is pulled low. I double checked on the LTM4622 demo board (DC2249B), and I was able to see both Vout's decay to 0V. 

    For your schematic, the only suggestion I would have for you is to change the frequency to 2MHz to reduce the inductor current ripple below the max of 1.2A mentioned in the datasheet (I see that you have tried this). Other than that, there are no obvious issues with your schematic.

    I have a few additional questions for you:

    • Are you able to disconnect V_3V3D from all downstream components that it might be connected to?
      • It would be best to isolate the LTM4622 as much as possible to see if the leakage is coming from within the LTM4622 or another component.
    • If you have multiple boards, do you see the same behavior on all your boards? 
    • Is DNL equivalent to Do Not Install?
      • If so, from the schematic that you copied, your application is:
        • VIN = 12V
        • VOUT1 = 1.2V
        • VOUT2 = 3.3V
        • Frequency = 1MHz (updated to 2MHz)
        • Mode = Burst
        • COMP1 is not connected to COMP2
      • Is the application above correct?