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LM337-N: Heat generation and ripple voltage.

Akira Sato
Prodigy 10 points
Part Number: LM337-N

We are using LM337N to generate -8V from -15V.
When the load current of the LM337N increases and its heat is generated,
there are individuals where the output voltage ripple increases and individuals where it does not.
-1 What is the cause of the increase in voltage ripple due to heat?
-2 Before mounting the LM337N on the board, I would like to select an individual that does not increase ripple
even if it generates heat. Are there any electrical characteristics that can be used as a selection criterion?

  • 0
    TI__Genius 12680 points

    Hello,

             Is the ripple being observed only under loaded conditions and are these units sharing the same supply? Ripple rejection (PSRR) is a critical characteristic of the LDO. CADJ (Capacitor between the ADJ Pin and GND) and COUT have a significant impact on PSRR. There is also a possibility that you are encountering a marginal stability issue due to insufficient ESR in COUT (hence some units are showing ripple while others are not). What value and type is the output capacitor? It would help us if you could share a schematic of your setup. Thanks!

    Regards,

    Srikanth

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 10 points

    Thank you for answering.
    Ripple can only be seen under load.There is one power supply. I replaced some boards and measured.
    In addition to the load on the board, I connected an external resistor to accelerate the heat generation.
    Of course, I chose a resistance value where Tj <120 (deg.C).
    We are sorry, but we cannot disclose the schematics because it is a customer's circuit.
    I understood that problems occur when the ESR of COUT is low.
    I also understood that selecting parts is wasteful because the conditions are critical.
    Thank you for your advice.

    Sato.