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LM2591HV: feedforward capacitor selection for ADJ version

FRANK1
Expert 7835 points
Part Number: LM2591HV
Other Parts Discussed in Thread: LMR16010, LM76002

Hi sir,

I am using ADJ version for 24V input and - 15V output.
The input capacitor of 330 uF electrolytic capacitor and 2.2 uF SMD cap are connected in parallel.
Output inductor 220 uH.
The 1.23V input to the FB terminal and use 27Kohm and 2.4Kohm as voltage divider resistance .
The output capacitor have 3pcs 10uF in parallel connection.

What is the selection of the feedforward capacitor for phase compensation at this time?
(capacity, rated voltage, temperature characteristics, frequency characteristics, etc.)

In particular, I want to know what the capacity is and what the rated voltage is above.
Thank you for your suggestion.
Regards,

  • 0
    TI__Mastermind 27045 points

    Hi Frank,

    What's the load current and input voltage range?

    B R
    Andy

  • 0 in reply to Andy Chen
    TI__Expert 7835 points

    Hi Andy,

    Thank you.

    The load current is unknown now and the input voltage range is probably about 24V ± 5%.

    If the feedforward capacitor cannot be selected in this information,
    in this circuit condition,

    How many volts does the rated voltage of feedforward capacitor require?

    Is there a temperature characteristic of feedforward capacitor?

    Is there a frequency characteristic of feedforward capacitor?

    Thank you for the advice.

  • 0 in reply to FRANK1
    TI__Mastermind 27045 points

    Hi Frank,

    The feedforward cap is not essential as invertering buck/boost converter require lower loop bandwidth. you can design it as place holder.

    You also take a look at LMR16010 or LM76002 which are new generation parts better for new design 

    B R

    Andy

  • 0 in reply to Andy Chen
    TI__Expert 7835 points

    Hi Andy,

    Thank you for your suggestion.

    but we wanna use LM2591HVS-ADJ/NOPB now.

    Please confirm the following questions.

    1. How many volts above the rated voltage of feedforward capacitor?
    In my design of the - 15V output circuit, 1.23V input to FB terminal with a partial voltage of 27Kohm and 2.4kohm.
    15×(27ｋ/(27k+2.4k))＝13.8V
    is it OK to use the feedforward capacitor of rated voltage above DC16V, or above DC16V?


    2. Are the temperature and frequency characteristics of feedforward capacitor specified?
    Is the temperature characteristic X7R and X5R OK?

    Thanks.
    regards,

  • 0 in reply to FRANK1
    TI__Mastermind 27045 points

    Hi Frank，

    For -15V Vout, the feedforward cap voltage rating should be 50V,

    Cap type depends on device temp in worst operating condition, better to use X7R as it can cover 125C temp range,  

    B R

    Andy