Dear,
good day!
we use ZSC31015 as piezoresistive bridge sensor signal conditioning to assemble pressure sensor. Everything runs smoothly. We meet strange thing that when we put the pressure sensor into use, if we add 100nF to 470nF capacitor at sensor output PIN to the ground to smooth the signal, about 2% products would occur Oscillation in output. The frequency is 42.117kHz and amptitude is 400 mVpp. if we remove the capactor, the output signal is fine.
why this phenomenon happen? could you list some factors caused this issue?
Many thanks and Best Regards,
Jarvis
Hello Jarvis,
Thanks for reaching out Renesas Engineering Community.
Would it be possible to share with us your schematics? I assume that you are not using the EVK.
The picture from the oscilloscope you sent I assume is when the capacitor is not connected is that correct?
Please let me share with you the resistor and capacitor limits depending on the programmed output mode:
Best Regards,
IK_Renesas
Dear IK,
Many thanks for your help! We add the capacitor and found the issue.
the schematic is:
the viedo is:
Why the oscillation does happen?
Jarvs
Dear Jarvs,
Could you kindly please check the private message I have sent to you and reply me?
IK
I work for Honeywell and the product is Trustability HSC sereis pressure sensor. this issue happend in out custoer site.
Thank you Jarvis,
Let me investigate further this and come back to you.
Many thanks for your support.
Our customer has used morre than 10k pcs. The failure rate is about 2%.
I guess the output short-circuit protection take action. I checked the datahseet, the short current limitation is from 3mA to 40mA. During the output charges the capacitor, the current is more than 3 mA and a few ZSC31015 is just in the low end.
Our customer's application schematic is easy to trigger oscillation when the pressure changes rapidly. I monitor the current in the output PIN. When oscillation happen, the output current reached 10mA peak-peak. The blue siganl it voltage, about 400mVpp and yellow signal is current, 10mApp
to solve the issue, I modify the circuit to see what happen. I only series one small resistor, the oscillation does not happen.
I do not know the oscillation mechanism. Can you help me?
Please let me inform you, that I checking this internally with the rest of our engineers and get back to you as soon as possible.
Thanks for your cooperation.
Do you have any posiive reply from Engineering team?
Yes, let me apologize for the delay!
If you will check the datasheet for this device and the maximum specified load capacitance is 15nF, which is far below for what you are using. As mentioned in my initial reply.
We assume that there must be some interaction between the output driver and VDD internally that is creating the oscillation you are observing.
If the filter capacitance is absolutely necessary for the application, then adding some small resistance makes sense. If it is much less than the input impedance of what the OUT pin is driving, this will not cause appreciable error, and it will additionally help with noise reduction.