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TLC7524 DAC in voltage mode does not give expected output when set up as in data sheet

Michael Strong
Prodigy 40 points
Other Parts Discussed in Thread: TLC7524, LM358

I have the TLC7524 setup in voltage mode as in data sheet and the highest voltage I can get with a +5v supply is 4.1v.

Any thoughts? I notice that the output in voltage mode is pretty weak, it doesn't want to drive 2 unity gain amplifiers (LM358s).

  • 0
    TI__Genius 10615 points
    Hi Michael,

    The voltage mode is not designed to support a VREF larger than 2.5V. This datasheet is very old and does not address this limitation clearly.
    Since you are using an output buffer, I would suggest that you use the amplifier as shown in Figure 3 of the datasheet.
    What are the goals of yous application? Maybe I can help you choose a newer device.
  • 0 in reply to Eugenio Mejia
    Prodigy 40 points
    The goal is to drive another unity gain amplifier (358) with the unity gain amplifier (358) stage after the 7524. The voltage range is from 1v to 4.8vdc on the second amplifier. The second amplifier (358) has a 1k pull-up to ~6v and a 5.1k to ground. The first stage op amp (358) is powered by +15v and ground.
  • 0 in reply to Michael Strong
    Prodigy 40 points
    In addition, the ~6v is also sourced by TL431B powered by +15v and there is a 100uF cap at the junction of the 1k and 5.1k. The first stage LM358 has trouble driving the second stage with the 100uF initially. So the first stage amplifier sees a small jump in voltage when trying to bias at lower voltages (1-2.5v) but in a second or two the output settles at the lower setting.
  • 0 in reply to Michael Strong
    TI__Genius 10615 points

    Michael,

    I would recommend using the circuit in Figure 3 of the datasheet. With this circuit you can set it to have an output of 0V to 5V (or 4.8V). Then follow it by your unity gain amplifier. I would also recommend using the capacitor shown between RFB and OUT1, this will aid with the spiking that you are seeing.