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LM2904B: Slew Rate simulation

Yuta Nishie
Genius 3665 points
Part Number: LM2904B
Other Parts Discussed in Thread: LM2904,

Hi,

I ran a slew rate simulation using LM2904 and LM2904B.

The circuit was the same, but the output voltage waveform was different. Could you tell me the cause of this?

LM2904B SR.TSC

LM2904 SR.TSC

■LM2904

■LM2904B

Best Regards,

Nishie

  • +1
    TI__Mastermind 28796 points

    Hey Nishie,

    This is caused by the models being different architectures. The LM2904 model you had included in your schematic was a simpler model developed by national semiconductor. We have since updated this model with a more complex architecture that shows more of the device behaviors.

    The newest model can be found at the below link under design tools and simulations:

    https://www.ti.com/product/LM2904#design-tools-simulation

    On the output of the LM2904, there is a 50uA constant current sink. This may result in some non-linear behaviors on the output when you switch between sinking and sourcing current. For more information on this please see section 3 in the below application note.

    https://www.ti.com/lit/an/sloa277b/sloa277b.pdf

    Shifting your input voltage up by 3V fixes this for the LM2904. LM2904B has a stronger constant current sink driver, so to fix this you have to shift your voltage and increase the value of your resistors to 10k.

    Best,
    Jerry