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DAC8871: maximum frequency

rodolphe archambault
Prodigy 30 points
Part Number: DAC8871
Other Parts Discussed in Thread: DAC8811

Hello,

What is the maximum frequency of a sinusoidal signal converted by DAC8871  ?

the datasheet indicates a maxi aquisition of 16x20ns + 30ns (tTD) = 350ns (or 2.86Mhz) for a sample => We can hope 1Mhz with shannon

The datasheet indicates also setting time 1uS to 1LSB to FS  ?  what does it mean ?

Thanks

Rod

  • 0
    TI__Guru 53573 points
    Hi Rod,

    The settling time specification means that the DAC with settle to within 1LSB of the desired output typically within 1µs. Figure 35 and 36 show this behavior, with the DAC transitioning from the extremes of its range. Generally, smaller voltage transitions will settle faster. What this specification means is that if you were trying to generate a fullscale square-wave, you would likely not be able to go beyond 500kHz.

    Your calculation is correct in regards to the maximum SPI sample rate of ~2.8MHz.

    You may be able to generate a 1MHz sinewave, though you need to take the amplitude into account. If you are trying to generate a full-scale sine wave with DAC output at 1MHz, then you will be expecting two full-scale transitions in 1µs, which would conflict with the settling time specification. You could consider generating a lower amplitude square-wave, then using an external filter to create the sine-wave.

    In addition, you could consider some of the high-speed DACs or MDACs, like the DAC8811.
    www.ti.com/.../dac8811.pdf

    This device is a faster, current output device.

    Thanks!
    Paul