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DAC7742: can not get a output

Jeff Xie
Intellectual 1780 points
Part Number: DAC7742

Hello,

My customer can not get a output of DAC7742. Below is the schamtic and capture wavefomr:, he wants to use DAC in direct mode, so LDAC is kept low.

Figure 1 

Figure 2 is the waveform of the corresponding pins when sending signal by STM32: yellow (R/W), blue (CS), purple (LDAC), green (RST).

Figure 2

  • 0
    TI__Genius 14220 points
    Hi Jeff,

    Thank you for your query. Due to local holidays, I will get back to you by end of this week.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    TI__Guru 53633 points
    Hi Jeff,

    I looks like he is violating the timing specification for this device. Page 5 of the PDS shows that R/W pin must be asserted low before the CS pin is by at minimum 10ns. The CS pin should also go high again before the R/W pin changes states as well. The DATA must be set on the lines before CS goes high again, as it latched on the rising edge of the CS line. Then the R/W line can change after that.

    Thanks,
    Paul