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Op-amp Required

Deepak Bansal
Expert 2395 points
Other Parts Discussed in Thread: TLC393, TLC339, TLC193, TLC372, TLC139

1. I have an application where I have to drive N-channel MOSFET depending upon signal from MSP430.Since MSP430 alone cannot drive the FETS, So I have put to op-amp between MSP430 & FETS. If conditions arises, MSP430 will drive op-amp, which will further drive FETS.

2. My circuit is battery operated & need to be very low current consuming.

3. Will Rail to Rail or open -drain  serve this purpose. As I think with a  voltage signal at op-amp input from MSP430, op-amp o/p can be driven to rails. Kindly suggest me the same.

4. Supply range: 7- 18V

5. High signal from MSP430 =3.0V, & Low signal=0.0V.

Regards,

Deepak

 

  • 0
    TI__Guru* 93105 points

    Hi Deepak,

    It sounds for your MOSFET driver application that an open-drain or open-collector comparator is a better choice than an operational amplifier. A comparator is specifically designed for switching applications and overcomes some of the drawbacks of employing an operational amplifier as a comparator. They are really designed to provide best linear operation performances. The MOSFET input capacitance charging rate and rate at which you have to switch the MOSFET will dictate the comparator's output current drive requirements and the pull-up resistor value required during output pull down. Note that the transient current while charging/discharging the input capacitance will be significantly higher than the cases where the MOSFET is just fully on our off. 

    CMOS comparators such as the TLC139, TLC193, TLC339 and TLC393 have very low supply current requirements, about 10uA per comparator section, can handle the 7 to 18V supply voltage and can sink as much as 20mA. If their speed isn't fast enough, the TLC372 is considerably faster. Its operating current is 150uA (max). A push-pull output comparator could also be used in the application but the device selection is more limited than it is for open-drain devices.

    Regards, Thomas

    PA - Linear Applications Engineering

     

  • 0 in reply to Thomas Kuehl
    Expert 2395 points

    Hi Thomas,

    Can you give me your mail-ID. I want to discuss it in more detail.

    Regards,

    Deepak

    SES

  • 0 in reply to Deepak Bansal
    TI__Guru* 93105 points

    Hi Deepak,

    My TI email is: kuehl_tom@ti.com

    Let's take your application off the E2E forum from here. Any information or schematics that you have might prove helpful in our private discussions.

    Regards, Thomas

    PA - Linear Applications Engineering

     

  • 0 in reply to Thomas Kuehl
    Expert 2395 points

    Thanks Thomas,

    Will send details on your TI's email ID.

    Regards,

    Deepak