• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 389 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LMZ34002: Alternate part number

LMZ34002: Can the output capacitor value be reduced to less than 100uF when the output current is 150mA with -12V?

Kazuya Nakai59
Guru 21595 points
Part Number: LMZ34002
Other Parts Discussed in Thread: LMZM23601

 Hello guys,

 One of my customers is designing a power supply circuit which uses LMZ34002 for their next products.

 But their product has space and height limitation. So they want to reduce the power supply output cpacitor value. Their output voltage and current is -12V/150mA. The input voltage is +12V.

 Can the output capacitor value be reduced to less than 100uF when the under the conditions? It the answer is yes, what is the minimum value?

 Also they want to use electrolytic capacitor for output capacitor because it has become difficult to get ceramic capacitors recently.

 Can the output ceramic capacitor be replaced with ceramic capacitors?  

   

 Could you please give me your comments or advice?

 Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.

  • 0
    TI__Guru 50120 points

    Hi Nakai-san,

    Let me get in touch with the apps engineer who might have more information on using these parts. Generally speaking, it is recommended to stick with the datasheet spec. In this case the minimum required external output capacitance is 100uF, which I suspect is for stability reasons.

    An alternative that I would propose is to the use the LMZM23601 and configure it for inverting application. Conveniently there is an application note that goes over this process. Please have it look at this link and let me know your thoughts. Do not that the input voltage tested was for 24V. This alternative solution would definitely require output capacitance than the LMZ34002. 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Nakai-san,

    Since you are running at a relatively light load, you can get away with using less output capacitance. I'd stick with using a 47uF at the output. 

    I've attached a pdf of a simulated theoretical Bode plot using your operating conditions: VIN=12V; VOUT=-12V; IOUT=150mA. This would allow you to cut your output capacitance by half while still being stable. It is still recommended to bench test the design to verify stability.

    LMZ34002_Theoretical_BodeSim.pdf

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    Guru 21595 points
    Hi Jimmy,

    Thank you very much for your reply.
    I will inform the customer your simulation data. Also I will introduced LMZM23601 and the application note.

    Your replies are very helpful for the customer and me.

    Thank you very much again and best regards,
    Kazuya Nakai.