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Original question:

LMZ22010: LMZ22010

LMZ22010: LMZ22010

Rozi Bachar
Prodigy 60 points
Part Number: LMZ22010

Hi,

Following our lab experiment with the LMZ22010 Evaluation Board,using the EN pin in 1HZ (according to your recomendation), we found that 1Hz is not good enough.
And we need to toggle the EN pin between 10HZ to 20Hz.
So my questions are :
1.Is it OK to work this way?
2. What is the maxmimum frequency to turn-on and turn-off by the EN pin?

Another question related to the SYNC pin:
In order to improve EMC performance, we think of using spread spectrum frequency modulation, LTC6902.
Meaning that the SYNC pin in the LMZ22010 wil be connected to the LTC6902 output.

I will be glad to have your opinion.
Thanks in advance



  • 0
    TI__Guru 50120 points

    Hi Rozi,

    Can you show me where in the datasheet and/or user's guide is the 1Hz recommendation? The datasheet specs the EN pin control with a certain threshold (1.274V) before the converter starts power conversion.

    I dont see an issue using the LTC6902 for spread spectrum frequency modulation since it is designed to provide a stable clock for switching regulators. Just make sure you operate between the SYNC range (314kHz to 600kHz). 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 60 points
    Hi Jimmy,

    First thank for the quick response.
    On Apr 25 2018 I sent here a question about our application and I got an answer from TI Employee.
    I hope you can see what was my question and the answer that I have got.
    Maybe I didn't understand the answer.
    So, I hope you can clarify the answer.

    Thank
    Rozi
  • 0 in reply to Rozi Bachar
    TI__Guru 50120 points

    Hi Rozi,

    I believe the question you are referring to is from this post. 

    You might be confused on the second paragraph that describes how to control the LMZ22010. To summarize Denislav's explanation, in order to completely turn the LMZ22010 on and off of power conversion you need to control the EN pin. This is in reference to your questiona: "Can I stop the LMZ22010 working by support '1' (zero Hz PWM frequency) to the SYNC pin for one second and after that support external clock for the next one second and so on...?" 

    Just to clarify, the SYNC pin is only used for external synchronization and does not affect whether the converter turns on or off. If you want the converter to switch a different frequency than the internal clock frequency, you will need to provide an external frequency source. When you are not planning on external synchronization, you must  "park" or tie the SYNC pin to ground which will result in the regulator to switch to its internal free-running PWM frequency of 359kHz. 

    Summary

    1. The LMZ22010 can be used for your TEC application
    2. Potentiometers can be use to tune Rfbt and Rfbb, just make sure that you have the appropriate output capacitance. Please note that a 2V application will require more output capacitance than a 6V, so you should design your output capacitance based off 2V application since you will be switching between 6V and 2V.
    3. Controlling the SYNC pin will not turn off the converter. It is recommended to control the EN pin to turn the converter on/off.

    Hopefully this helps put things into perspective. Let me know if you need anything else.

    Regards,

    Jimmu

  • 0 in reply to Jimmy Hua
    Prodigy 60 points
    Hi Jimmy,

    I think I understand my mistake, thank.

    But according to our new tests, we need to work with constant 6V only and then 0V (there is no need for 2V).
    Which mean we need to turn on and off the LMZ22010's output in 10Hz (maybe more).
    Is it make sense to toggle the EN pin in that frequency?
    Or maybe the LMZ22010 can not be used for our TEC application...

    Please advice

    Thanks
    Rozi
  • 0 in reply to Rozi Bachar
    TI__Guru 50120 points

    Hi Rozi,

    If that is the case, then just make sure to design the output capacitance based on 6V. I don't see an issue toggling the EN pin to dynamically control the part on/off. If anything it would be easier to implement a 6V to 0V power sequence through controlling the EN pin HIGH/LOW.

    Regards,
    Jimmy