pin control for EVAL-ADA4255

Hi nysato,

Apologies for the late response. 

nysato said:

Away from software control, I like to control the gain through pin-header (GPIO0～GPIO7).

The gains of ADA4255 cannot be controlled using the GPIOs. You can only control them using the SPI pins - CS, SCLK, SDI, SDO. See image below for the SPI Interface:

To control the SPI interface, please refer to the registers below:

Also kindly take note of the voltage levels of the digital pins:

Regards,

Kristine

Dear Kristine,

Thank you for your answer.
Sorry, still my brain do not catch how to control the gain by pin header without EVAL-SDP-CS1Z.

G3, G2, G1, and G0 in Table 12 correspond to CS, SDI, SDD, and SCLK in the SPI pins, thereby, we can apply the DC bias voltage (no serial control) to their each pin in the SPI pins surrounded by yellow line.

As the begginer question, please explain me how to change the register information by using the combination of DC bias voltage applied to pin header ?

Is it possible that ？

I hope you keep in touch with me continuously.

Warm regards, Naoyuki

Hi Naoyuki,

You need to connect the SPI pins to your microcontroller to connect the gain. ADA4255's gain settings cannot be controlled by connecting the SPI pins to a high/low voltage. For more information on SPI interfaces, you can check out this article - Introduction to SPI Interface. Once you have connected your microcontroller to the SPI pins of the evaluation board, you will now write the desired gain register(you can check this out on my previous answer or from the register summary in the datasheet) from the controller then it will transfer this data and control the amplifier. I would also like to clarify that the G0, G1, G2 and G3 does not correspond to the SPI pins in the yellow box. You can also check out the SPI interface discussion specifically for ADA4255 here.

If you want to use DC bias voltage to control your PGIA gain, logic-programmable InAmps would be the best fit. I'm not quite sure of your other requirements but for instance, I would recommend checking out LTC6373 and AD8250.

Hope this helps!

Kristine