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LM27762: Unable to simulate the LM27762 in WEBENCH

Andy Khan
Prodigy 65 points
Part Number: LM27762

I'm using the LM27762 to generate +5 and -5 voltages and I would like to use WEBENCH to simulate performance with various capacitors and resistors, as mentioned on page 13 of the datasheet.   When I choose LM27762 in WEBENCH (webench.ti.com/.../switching-regulator)  it says "Sorry, we could not find LM27762".  I also can't get it to find the part when I enter my input and output voltages.  I would like to see the switching waveforms at my expected current load.

In the meantime, I'm trying to reduce the output resistance on the -5v output because I'm only achieving -4.6v at my load of 60mA. What is the value of Rsw to use in Equation 2? With no load current the voltage measures -5v, so I know the feedback resistors are correct.

My input voltage is 5.5v and I'm using these components:

R1 237k

R2 75k

R3 255k

R4 82.5k

C1 0.1uF (flying capacitor)

Cp. 4.7uF

  • 0
    TI__Mastermind 21150 points

    Hi,

    LM27762 is not available on Webench.

    The best way would be to order an EVM and perform the desired tests.

    Andy Khan said:
    In the meantime, I'm trying to reduce the output resistance on the -5v output because I'm only achieving -4.6v at my load of 60mA.

    Did you use an EVM?

    Thanks,

    Febin

  • 0 in reply to Febin
    Prodigy 65 points

    I have the circuit on my PCB and I am testing it there.  I downloaded TI SPICE and was able to simulate it.  What is the value of Rsw in the datasheet equation?

  • 0 in reply to Andy Khan
    TI__Mastermind 21150 points

    Hi Andy,

    If you want to calculate the drop for each of the rails, then you could use the Rout and LDO drop out values from the plots (Fig 3 & 4) / Elect Char table in the datasheet.

    I don't think you need the Rsw value. All the losses related to the device are accounted and the final Rout is given in the datasheet.

    Regards,

    Febin