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LMZ22005 and LMZ12001 minimum input voltage

Maxime Puech
Prodigy 140 points
Other Parts Discussed in Thread: LMZ22005, LMZ12001, LMZ31506

Hi,


I am using a LMZ22005 Simple Switcher for generating 3.3V power supply, and I need some clarification about its minimum input working voltage. I found some contradiction in the datasheet :

- The LMZ22005 datasheet says that its input voltage range is [6V ; 20V] on page 1

- But on page 3 it says that it is [7V ; 20V] for 3.3V output voltage

- But in the same time, on page 6, there is a figure that shows 3.3V operation with 6V input voltage (fig. 8)

Is the minimum input voltage 6V or is it 7V for 3.3V operation ? What happens is this is 7V and its actual input voltage is 6V ? This is really important for me as I will be using a 2 cell Li-Ion battery with a voltage that can be as low as 6V.

I also have a similar problem with the LMZ12001. I need to generate a voltage of at least 3.7V with an input voltage that can go as low as 6V. What is the LMZ12001 minimum input voltage for 3.7V operation ?

Thank you for your help,

Regards,

Maxime Puech

  • 0
    TI__Genius 16025 points
    Hi Maxime,

    The minimum input voltage for the part is indeed 6V. However this doesn't necessarily apply for the full Vout range. At lower Vout's (lower than 3.3Vo) it is easily achievable. However as Vout begin's to increase, we begin to hit maximum duty cycle limitations that can be adjusted by dropping the frequency using the Sync pin.

    If using Sync to lower the frequency is not an option, then the datasheet specifies that for 3.3Vo, 7Vin was tested and ensured as the min operating input voltage over temperature.

    Hope this clarifies your query.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Prodigy 140 points

    Hi Anston,

    Thank you for your answer.

    How do you explain this figure (page 6 on the LMZ22005 datasheet) :

    It is the only place in the datasheet where the 3.3V performance is specified with a 6V voltage input. Is it a mistake ?

    If I understood well I should drop the  LMZ22005 PWM frequency to 650 kHz in order to be able not to hit the LMZ22005 maximum duty cycle. I don't think I will do that as generating a clock is a relatively heavy solution.

    Does TI have other Simple Switcher references that can meet my needs ? I need to generate 3.3V / 5A (max) with an input voltage of 6-9V.

    Regards,

    Maxime.  

  • 0 in reply to Maxime Puech
    TI__Genius 16025 points
    Hi Maxime,

    Please check out the LMZ31506 as a possible solution.
    www.ti.com/.../lmz31506.pdf

    This part can handle up to 15Vin down to 4.5Vin.
    And output to your specs.

    Please also try out Webench which is a tool to help you select the Bill of Materials, provides schematic and full layout.

    It is available on the front page of www.ti.com.

    Thanks,
    Anston