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LM3488: Select the DC-DC boost device

user4674678
Intellectual 490 points
Part Number: LM3488
Other Parts Discussed in Thread: LM5000, LM5002

Hi team,

Now I am designing a gas sensor circuit. In my circuit, I want to design 3.3V boost to DC40V ~45V voltage. Because I use 40V or 45V as the electrode voltage. When there is some VOC gas 

in the electrode. The electrode can ionize the gas. Then it will generate the low current in the  electrode. After this I will capture the low current signal with the op amp and ADC.

The low current maybe 1nA~1uA. So, now I need to output DC40V~45V voltage. Since my board size is very small. So I need the package of the DC-DC device should be the smallest. 3mm*3mm wii

be the best. 

Q1: And I found LM3488 and LM378 can meet my requirement. Is this correct? If this is correct, can you send me the circuit? 

Q2: Or you have any other ideas?  Can the charge pump  achieve my requirement? 

Q3: Since my output current is very low. So the package of the inductance will be very small ,correct? If the package of the inductance is large, it will not  good for my design.

For my above requirements, would you help me ?

  • 0
    TI__Mastermind 21720 points
    Hello,

    The load current is only 1uA? Please confirm.

    -Garrett
  • 0 in reply to Garrett Roecker
    Intellectual 490 points

    Yes, the max load current maybe 1uA. I want to explain my application again. 

    There is some anion of the gas between the  positive and negative electrodes. The  positive electrode should be connected to 40V~45V voltage.

    The anion run, Then it will generate the low current. The max current maybe 1uA. So, I have to select a DC-DC boost device that can boost from 3.3V to 40V~45V.

    Q1: Do we have any suitable device?

    Q2: If we do not have the suitable device, can I use this boost circuit like the attach? Or do you have any other ideas?

    Can you send me a correct TINA circuit that can boost from 3.3V to 40v~45V?

    Please check the attach. Can you tell me how much the value of L1 can be set? And how can I set VG1? 

    Q3: If I use MCU to control the Gate of the MOS, how much is the frequency and the duty cycle can I set?

  • 0 in reply to user4674678
    TI__Mastermind 31315 points
    Hi,

    A combination of a boost stage and charge pump stage should work. Please refer to the following designs in this link:

    www.ti.com/.../PMP20212. This should be a good starting point.
  • 0 in reply to Richard Fu22
    Intellectual 490 points
    Hi Richard,

    The link that you sent cannot achieve my requirement. The min input voltage is 9V. But my input voltage needs to be 3.3V.

    Can you have any other good ideas? How to achieve my requirement through a combination of a boost stage and charge pump stage?

    Can you sent me a TIAN circuit? Or any other circuit?
  • 0 in reply to user4674678
    TI__Mastermind 21720 points
    Hello,

    Due to the current of this application being quite low there are not a lot of good solutions. A good place to start looking is the LM5000 and LM5002. This are high voltage low current converters with an integrated FET.

    The TINA model for the LM5002 can be found here.
    www.ti.com/.../snvm532

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Intellectual 490 points
    Q1: The max duty cycle of LM5002 is 85%. For my requirement, if the output is 45V, the duty cycle should be 93%.
    So LM5002 cannot meet my requirement. Can you confirm this?

    Q2: For my above TINA circuit, can you send me a correct TIAN circuit to achieve my requirement?
  • 0 in reply to user4674678
    TI__Mastermind 21720 points
    Hi,

    Even though there is a maximum duty cycle the circuit can be designed to operate in discontinuous conduction mode (DCM). this will allow for a high step-up ratio at a much smaller duty cycle. This will also allow for a reasonable inductor value since the current is going to be small.

    Thanks,

    Garrett