• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 47 subscribers
  • Views 1784 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM2904: How do I tell the difference between the LM2904B and LM2904?

Rob Frohne
Expert 1505 points
Part Number: LM2904

Hi,

Reading the datasheet for the LM2904 and LM2904B I find a critical difference between the LM2904 and LM2904B is that the LM2904 specifies the output voltage swings down to 20 mV from ground if you are powering it on +5V and ground with RL < 10K, at least the way I read it.  The LM2904B will only go to a volt above ground if I read the datasheet right.  I purchased LM2904DR op amps from Digikey.  They seem to clip at 0.65 volts above ground which makes me think I got LM2094B op amps instead of LM2904 op amps.  How do I tell what I need.  I thought I had picked LM2094 not LM2904B, by pinking the LM2904DR, but I must be wrong, or something.  Can you help me figure this out?  If a schematic will help, I can help, it is attached here.

Thanks,

Rob

  • 0
    TI__Guru**** 152796 points

    Rob,

    LM2904 and LM2904B are very similar products. The big difference is the method used to measure VOL (low output swing).

    Notice that LM2904B has to sink 50uA at low voltage and 1mA upto 1V.  LM2904 doesn't have to sink any current to get 20mV or less. The output would be zero if the LM2904 was removed from the board. The LM2904 must not source current at 20mV. That was an impressive feat forty years ago when this spec was written. 

    LM2904 does have an (25C) output current specification at Vo=200mV, it is 12uA minimum. For LM2904B that minimum current at 150mV is 50uA. 

    See page 9 of the application note for these devices. http://www.ti.com/lit/pdf/SLOA277?jktype=tech_docs

  • 0 in reply to Ron Michallick
    Expert 1505 points

    Thanks Ron,

    That solved it.  The sound card we were hooking up to was sending current back into the op amp, and the emitter follower in the output of the op amp was going into cutoff.  We needed 180 ohms extra load to solve it.  Thanks for the great tip!

    Rob