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LM3488 very low Vsupply

Jeppe Odgaard
Prodigy 20 points
Other Parts Discussed in Thread: LM3488

Hi!

I'm developing a boost converter that uses a 3,9V supply and boost a 0,5V input to a 3,9V output. The current is also quite high (some amps), so there is some loss in the external components.

Therefore I've chosen the LM3488 since it can provide a 100% duty cycle. I want a high duty cycle because the losses is probably going to be quite high.

This is the setup I'm testing (V2 is 0,5V):

I'm experiencing a 100% duty cycle, which means the MOSFET never starts switching.

I've tried:

 - changing the supply voltage between 3 to 10V.

 - changing R4 to 40k.

 - changing input from 0,5 to 3V.

 - connecting a 5,7 ohm resistor between DR and the MOSFET gate

How is it possible to make the DR duty cycle become close to 100%, without getting to 100%?

Thanks in advance.

  • 0
    TI__Guru 64365 points

    You will need to feed the switch current information into the Isense pin for this application to work.

    I understand that you can not afford too much voltage drop with such a low input supply, however you can not get around this requirement.

    You may be able to use a very small sense resistor and amplify the signal to the Isense input; a high speed, low offset op-amp would be

    required.

    Frank D

     

  • 0 in reply to Frank De Stasi
    Prodigy 20 points

    Thank you for the quick reply!

    I've tested the setup with a 7m ohm resistor now and this is working from 0,8V-3,9V.

    I think it's the gate charge of the mosfet that limits duty cycle and therefore the input range.

    Thank you for your support :)