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LM2841 inverter

Lutz Naumann
Expert 6110 points
Other Parts Discussed in Thread: LM2841

Dear Team,

can the LM2841 be recommended as an inverter generating a -15V of a +15V? Iout max on the neagtive rail is 90mA. Obviousely it seem to work and the converter appears to be stable but we were wondering if there was some internal compensation we have to watch out for. A competitors device can not be used as inverter due to internal compensation problems.

Do you perhaps have a circuit proposal that we could look at as we want to do further optimization on efficiency?

many thanks

Lutz  

  • 0
    TI__Genius 15810 points

    Hello,

    Theoretically the LM2841 can be employed in a Buck-Boost topology. The max sw voltage of the LM2841 is 42V. For your design the max switch voltage would be 15+15 i.e. 30V. The average inductor current for your requirements would be about 200mA. Therefore, yes the LM2841 should be able to work in that topology.

    But stability is another issue. This device is internally compensated with the compensation zero occurring around 11 kHz. In the buck-boost topology you have an RHP zero caused by the inductor which should be away from the bandwidth. This zero will depend on the duty cycle, load resistance, and the inductance value. If you choose the inductance value to get about 50% ripple current, it will help to push this RHP zero out at higher frequencies. 

    I do not have another schematic to show you, but for your requirement, a quick run through of calculations suggest that you start with 47uH inductor and 100uF output capacitor. A small value ceramic may be added in parallel. I hope this helps.

    Regards,
    Akshay