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LM317L: LDO Maximum Load Current

Kevin Gordon
Prodigy 30 points
Part Number: LM317L
Other Parts Discussed in Thread: LM337L, LM317, LM337-N

Tool/software:

Hi,

I am using TI's LM317L, LM337L, and TPS76350DBVR LDOs in my daughtercard transformer circuit to provide various output voltages; e.g. +/-12V and +5V. What is the maximum load current each LDO can handle? If the data sheet explains this specifically, please point me to the exact page.

Thank you,

Kevin

  • 0
    TI__Expert 3805 points

    Hello Kevin,

    The LM317L has a maximum guaranteed peak output current of 150 mA if the differential voltage across input and output (VI – VO ) is 35v. if 3V ≤ VI – VO ≤ 13V, there is a peak typical current of 200 mA, but we do not guarantee a maximum current. Please find this information in the table of section "5.5 Electrical Characteristics"  

    It is recommended that the output current is limited to 100 mA and you will find the specification in the table of section "5.3 Recommended Operating Conditions" on page 4. Please note that there is a minimum current of 5 mA in the new chip required to maintain regulation as specified in the table of section "5.5 Electrical Characteristics".

    https://www.ti.com/lit/ds/symlink/lm317l.pdf)

    The LM337L has a current limit of 120 mA if |VIN – VOUT| = 40 V or 320 mA if 3 V ≤ |VIN – VOUT| ≤ 13 V as specified in the table of section "6.5 Electrical Characteristics". Please note that there is a minimum current of 5 mA if |VIN – VOUT| ≤ 40 V or 3.5 mA if 3 V ≤ |VIN – VOUT| ≤ 15 V required for regulation, also specified in the table of section 6.5.

    https://www.ti.com/lit/ds/symlink/lm337l.pdf

    The TPS76350DBVR has a current limit of 1.5 amperes as specified in the table of section "11 Electrical Characteristics", but it is recommended to limit the output current to 150 mA as specified in the table of specification "9 Recommended Operating conditions". Please note that there is a recommended current of 1 mA needed to maintain regulation as specified in the test conditions at the table of section "11 Electrical Characteristics"
    https://www.ti.com/lit/ds/symlink/tps763.pdf

     

    Best regards, 

    Daniel Esparza

  • 0 in reply to Daniel Esparza
    Prodigy 30 points

    Thanks Daniel,

    This answers my questions about each LDO. I did read the data sheet, but wanted to make sure I understood correctly. Really appreciate your help on this.

    Enjoy,

    Kevin

  • 0 in reply to Kevin Gordon
    TI__Expert 3805 points

    You are welcome, Kevin.

    Please be mindful of the Power dissipation across the pass element in your design; make sure the thermal impedance and the power dissipation will keep the junction temperature below the recommended operating temperature. Also, review the section where we recommend the type or capacitance values and calculate it with the DC bias capacitor derating in mind.

    Best regards,

    Daniel Esparza

  • 0 in reply to Daniel Esparza
    Prodigy 30 points

    Hi Daniel,

    Very good information, thanks again. However, I would like to add some additional information to clarify my complete circuit, see pictorial below:

    VIN - VOUT in both cases for LM317L/337L, the conditions are not being met (unless I am misunderstanding); for 317L VIN (14.4V) - VOUT (12.76V) = 1.64V, for 337L VIN (-14.42V) - VOUT (-12.66V) = -1.76V. Does this mean the minimum (max peak, current limit, resp.) applies in both cases or there could be something wrong with my circuit?

    Regards,

    Kevin

  • 0 in reply to Kevin Gordon
    TI__Expert 3805 points

    Hi Kevin,

    Can you please also share what is the nominal operating current expected on each regulator to your load(s)?

    Best regards,

    Daniel Esparza

  • 0 in reply to Daniel Esparza
    Prodigy 30 points

    Hi Daniel,

    Speaking to the actual circuit designer, he says the nominal operating current "should" be ~350mA. When I first started debugging this circuit, the current load appeared high and the LDOs were quite warm to the touch. This led me to believe the LDOs were being over loaded, which eventually lead to the question of how much current load can the identified LDOs handle. I hope this helps.

    Thanks again,

    Kevin

  • +1 in reply to Kevin Gordon
    TI__Expert 3805 points

    Hi Kevin, 

    If the nominal operating current is 350 mA, you may need to select LDOs with higher current compliance like the LM317 and LM337-N.

    Unfortunately, they don't have the same footprint as the low current version.

    For the 5v regulator, you can use TLV75801PDBVR.

    Best regards,

    Daniel Esparza

  • 0 in reply to Daniel Esparza
    Prodigy 30 points

    Thanks again Daniel,

    I'll follow up as necessary once I get my pcbs in house and start my validation work.

    Enjoy,

    Kevin

  • +1 in reply to Kevin Gordon
    TI__Expert 3805 points

    You are welcome, Kevin.