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LM2703: Diode replacement

Ilya Mazurenko
Expert 1300 points
Part Number: LM2703

Hello Team!

Could you help please.
My customer have question about LM2703:
In their devices they are using LM2703
Vin =  2.4 to 5V, Vout = 7.2V, I_load = 20 - 30mA continuous (max).
As diode(datasheet's figure 6.) they used BAS316(NXP/Nexperia). But now it is discontinued. And they are looking for replacement.
In datasheet described it should have Switch current limit from 260 to 400mA. 
BAS316 has continious forward current - 250mA(max).
So there are questions:
1)This way with BAS316 the circuit works more than 10years without faults. How is it possible?
2)Which I_load is the maximum for the LM2703 with diode like BAS316?
They have 2 replacemnts from ONS: BAS16HT1G and MMDL914T1G. But their continuous forward current is lower = 200mA(max), repetitive peak forward current) = 500 mA (max).
Can they use one of this diodes with LM2703? 
In LM2703's datasheet described it should have diode like MBRM130LT1 with continuous forward current) = 1 A (max), IFRM (repetitive peak forward current) = 2 A (max).
Can they use variants with lower parameters?

Thank you in advance!

  • 0
    TI__Mastermind 21720 points
    Hi Illya,

    Thanks for getting in contact with us to answer your questions.

    In the datasheet, I do not see the reference to the diode BAS316 that you mention. However the rate continuous current of the diode can be less than the peak current limit of the device. This is due to the diode only conducting in during the off-time of the internal MOSFET. This means that the average current of the diode is smaller then the peak current limit because it doesn't conduct the entire switch period.



    Selecting a diode will be dependent on the application.The average current of the diode can be estimated as below.

    ILim*(1-D)

    Where:

    ILim is the worst case current limit
    D is the duty cycle of the boost converter.
    Once the average current is calculated, a little bit of margin should be added when selecting a diode with a large enough average current rating to allow for tolerances.



    Thanks,


    Garrett
  • 0 in reply to Garrett Roecker
    Expert 1300 points

    Hello Garrett,

    Please help us to solve the problem with the customer:
    They want to be sure, that LM2703 will work without faults with diode like BAS316.(They have already made first 10K devices with BAS316)
    But there are no any formulas for needed diode in LM2703's datasheet.
    If we will not provide some information to them, they just can make the p2p replacement for LM2703 - AP3015A(Didodes have formulas that insure the circuit will work without faults with BAS316)

    Thank you in advance!

    Vin = 2.4V to 5V, Vout = 7.2V, I_load = 20mA continuous (max)

  • 0 in reply to Garrett Roecker
    Expert 1300 points
    Garrett,

    Could you help us with information for the customer?
  • 0 in reply to Ilya Mazurenko
    TI__Mastermind 21720 points
    Ilya,

    Please see equation 3 of the datasheet.
    www.ti.com/.../lm2703.pdf

    Thanks,

    Garrett