Square wave output issue, is it noise ?

Thread Starter

captoro

Joined Jun 21, 2009
207
Hello fellows,

I am having issues with a MOSFET driver ISL55110 output. The source is a clean square wave. The ISL55110 seems to generates noise on the output and seems to get worst as the frequency goes up. I added a few snap shot at different frequencies. I have a 10 ohm resistor on the ISL output. After seeing this noise I added a capacitor 22pF and 100pF on the output and no changes. I have my circuit on a PCB. The traces are short. The capacitor I added is placed after the 10 ohm resistor and is grounded.
The PCB has four layer, the signal on the top and ground on the second.

Can someone point me to the right direction to fix this issue?
Ken
 

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LowQCab

Joined Nov 6, 2012
4,063
What type of Load is the MOSFET controlling ?
FETs have 3 parasitic Capacitances, 2 of which will transfer 'Ringing",
or other Electrical-Noise from the Load, back into the Gate-Pin.

Increasing the value of the Gate-Resistor may actually make this type of problem worse.

Do You have any Resistance between the FET-Source-Pin and Ground ?
Do You have any Resistance between the Gate-Driver and Ground ?
Are either of these connections via a PCB-Trace ?
The Gate-Driver should be positioned as closely as possible to the FET,
and MUST have the manufacturer recommended Bypass-Capacitors in
very-close proximity to the Gate-Driver.

Not all Gate-Drivers are created equal,
does your Gate-Driver deliver enough Current to control your FET-Gate adequately ?
.
.
.
 

Thread Starter

captoro

Joined Jun 21, 2009
207
hello,
thanks for taking time to answer. I removed the MOSFET to better see the ouput on the driver. The Snapshots are with no MOSFET. I did get identical results with the mosfets.
I may be thinking there is an issue with the driver.
 

BobTPH

Joined Jun 5, 2013
8,938
I don’t think measuring with the gate disconnected tells you anything useful. The driver is not designed to operate with no load. What does it look like with the gate connected?
 

Thread Starter

captoro

Joined Jun 21, 2009
207
I get the same results with the MOSFET connected.
I have another PCB, I will populate it and try again, maybe its a component issue. I will poste the results soon.
I have never seen this kind of output, its not your standard ringing or noise, so maybe one of you had seen this waveform before
 

Thread Starter

captoro

Joined Jun 21, 2009
207
Yes I do have bypass capacitors, So the issue was a faulty ISL55110 chip. It pobably turned bad during the soledring, AT low frequencies its works not at high.
Anyway Issued resolved, Thanks for inputs from all of you. Very appreciated to have a community like this one.
 
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