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DAC8871: Precision Data Converters Forum

Dukel
Intellectual 610 points
Part Number: DAC8871
Other Parts Discussed in Thread: TS5A3166-Q1, TINA-TI

Hi,

I'm building a circuit that includes the DAC8871. According to the datasheet page 16, it recommends that the CS (chip select) pin is connected to VDD trough a pull-up resistor.

I want to use a Raspberry Pi GPIO pin to control the CS. To ensure a proper startup I was thinking to connect the CS to VDD like stated in the datasheet and use an analog switch or a FET to control the CS pin.
I used a MOSFET before as a switch but never a analog switch like the TS5A3166-Q1. It should look like the circuit below. Unfortunately there is no TINA-TI SPICE model for the analog switch or similar products.

My question is will this work and how do I connect the pins of the analog switch to create the situation in the image.

Best regards,

Dukel

  • 0
    TI__Guru 53623 points
    Hi Dukel,

    I do not know think you need to implement the switch. A simple 10kohm pull up to the digital supply voltage should be fine. Once the MCU is initialized you can very that the state of the pin is high. In addition, you can also connect a GPIO to the RST pin, and just issue a power on reset to the DAC once the system is initialized, this would ensure that startup issues would be cleared (if any).

    Thanks!
    Paul
  • 0 in reply to Paul_Frost
    Intellectual 610 points

    Hi Paul,

    So I can just connect it like the figure below. Where the SW-SPDT1 is the GPIO and either is set to 0 or 3.3V. In my case the VDD 3.3V and GPIO both come from the same source (Raspberry Pi), but if the VDD was connected to another source and be a bit more or less ten the GPIO (3.3V) wouldn't there be any dissipation? 

    Best regards,

    Dukel

  • 0 in reply to Dukel
    TI__Guru 53623 points

    Hi Dukel,

    Yes, there will be some current flowing between the supplies/GPIO, but it is limited by the 10kΩ resistor.  Even if the GPIO is 0V, there is 330µA flowing into the pin.  You could also increase the resistor value to reduce this.  Also, the purpose of the pull up is to set the state high if the GPIO is in the high-z state (input).

    Thanks!

    Paul