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LM2734 BOOST feedback voltage

Paul Carson1
Prodigy 210 points

Using LM2734ZMK to provide an output typically 5.8V (6V max with tolerances over temp).

Datasheet specifies max voltage on BOOST should be 5.5V if using feedback diode into BOOST.

Our diode has a Vf=0.6V. Can I actually add 0.6V to 5.5V = 6.1V and use this as our Vout limit? And therefore conclude our current 6V max is safe?

  • 0
    TI__Guru**** 191445 points

    The maximum recommended BOOST to SW voltage is 5.5 V.  If you are charging BOOST from Vout (max 6 V) and you are absolutely sure the voltage fdop across your diode will never be less than 0.5 V, then you will not exceed the maximum recommended voltage.  I do have one question.  You state that your target output voltage is 5.8 V.  Why do you think that the regulation will be so poor as to allow the output to go to 6 V?  It should not vary that much.

  • 0 in reply to JohnTucker
    Prodigy 210 points

    Hi John, I am using 1% 100ppm resistors on the feedback and my calcs show up to 6V.

    Assuming 1% 100ppm resistors
    Typ Min Max
    Vref = 0.8 0.792 0.808 Volts
    R1 = 47 46.295 47.705 kOhms
    R2 = 7.5 7.6125 7.3875 kOhms
    Vo = 5.81 5.61 6.03 Volts
    Power R1= 5.3E-04 5.0E-04 5.7E-04 Watts
    Power R2= 8.5E-05 8.2E-05 8.8E-05 Watts

    Is this incorrect?

    Thanks,

    Paul