Tool/software:
Hi
I have asked this question before regarding Vref1 is not unstable, I did below suggestion but non-working properly:
1. Add pull down resistor of <470K to vref1, however that did not solve the issue Entity.
2. Decrease Vref2 series resistor which make the condition worse.
Also you can see on datasheet talk about this issue on 8.1.7. suggest to add pull down and capacitor, which I did
Ven =3.3+0.6 = 3.9
Ibia = (5-3.9)/200k = 0.0000055
Rpul = 3.3/0.0000055 *0.75 = 450K (I have replace C63 to this)
Please let me know what I am doing that cause this issue.
Thanks
Hi
I end up using 400K to 470K for pull down but still you can see little swings in oscilloscope. Reducing Cref1 resistor to 100K cause more spike in Vref2 voltage. This is even got worse during the conducted immunity when the logic translator is enabled.
THanks
Hi Amir,
Is it possible to solder a large PD resistor and decoupling cap on the same SM footprint?
I am wondering if removing C63 in place of the PD resistor is causing more ripple.
Regards,
Tyler
Hi Tyler
I have tried do that and add 0.1uf and 1uf in same place but the result is not that much different.
Thanks
Hi Amir,
What is the device you are using to supply the VREF1 voltage?
Regards,
Tyler
Hi Amir,
I am not an expert on LDO's, but the electrical characteristics of the datasheet for NCV8165ML330 look to have IOUT = 1mA unless otherwise noted.
Is there an issue with running the LDO at very LOW current draw? With 100k PD resistor, the LDO will have a load that is pulling in the uA range. What happens to your case when you have a PD resistor = 3300 ohm which would effectively draw 3.3V / 3300 ohm = 1 mA?
Regards,
Tyler
Hi Tyler,
I will test this by adding a drop down resistor right next to regulator
Thanks
Hi Tyler,
You are correct the load on regulator was not enough to regulate, so by adding resister fix the problem.
Thanks