topic NVT2006 Signal conditioning in Other NXP Products

NVT2006 Signal conditioning

wdunkley — Mon, 06 Mar 2023 17:10:27 GMT

I'm connecting to an A/D from an NXP IMX8M mini, 1.8 V on A side 3.3 V on B side.

I have two questions about signal conditioning. The MISO on "A" side is very wavy(It is the yellow one) does anyone have any recommendations on how to fix that?

(A side MISO @ 1.8 V Yellow)

(B side MISO @ 3.3 V Yellow)

My second question, is it normal for the B side MISO voltage to be so low? The digital Voltage supplied to the A/D is 3.3V and I've changed the Pullup resistors to 700 Ohms. The blue is the B side Clk btw.

Re: NVT2006 Signal conditioning

Manuel_Salas — Mon, 06 Mar 2023 19:39:31 GMT

Hello @wdunkley !

The MISO on "A" side is very wavy:

You can try putting Pull-up resistors in the MOSI and MISO signals. You can refer to AN1127.

In the chapter 5 (Applications) of that application note, you can find that the pull up resistor may be needed, depend of the application, in your case, it is a SPI communication, and I believe that the pull up resistors are needed. So, in chapter 5.2 is explained the cases when is necessary to put the pull-up resistors.

Other thing that I could see, the RC circuit between 200K resistor and the 1uF capacitor. The enable time and the disable time are essentially controlled by the RC time constant of the capacitor and the 200k resistor. In the application note is used a 0.1uF capacitor that is so smaller than yours (1uF).

Is it normal for the B side MISO voltage to be so low? The digital Voltage supplied to the A/D is 3.3V and I've changed the Pullup resistors to 700 Ohms.

In this case you can try to increase the resistors, may be to 10K instead of 700 Ohms.

Best regards!

Re: NVT2006 Signal conditioning

wdunkley — Mon, 06 Mar 2023 20:16:42 GMT

Could you explain why a larger Pullup resistor would raise the B side voltage? It seems like a lower resistor would help with that more. Thank you for letting me know about the capacitor. I will change that to a .1 uf.

Re: NVT2006 Signal conditioning

Manuel_Salas — Fri, 10 Mar 2023 17:51:09 GMT

Hello!

A higher pull-up resistor can also help reduce signal distortion and noise. So, a higher pull-up resistor value reduces the amount of current flowing through the line, which in turn reduces the amount of EMI picked up by the line. In other words, a higher pull-up resistor value means that there will be less current flowing through the resistor when the signal line is pulled low. This can help reduce power consumption, as less current means less power dissipated in the resistor.

In this case is recommended to use the 10K resistors as explain the attached application note.

Best regards!