• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Having floating copper pour connected to thermal pad on IC invites noise problems?

Status
Not open for further replies.

Flyback

Well-Known Member
Hello,
We have an offline LED driver IC which is of the switched linear regulator type. The IC has a thermal pad on it. However, its datasheet does not say to which pin the thermal pad should be connected. If we connect the thermal pad to a bottom layer copper pour on the PCB, then we can’t leave this pad floating. –Because as you know, floating copper pours on PCBs generate all kinds of noise problems?
Do you agree that leaving the copper pour which connects to the thermal pad ‘floating’ will invite all manner of noise problems…specially since on our tiny PCB, this ‘floating’ pad will be near the microcontroller and all the PCB traces leading to the microcontroller.
The LED Driver IC is DT3007B by Seoul semiconductor, and we have requested the datasheet from [email protected] but get no reply. The datasheet is nowhere to be found on the web.

The IC is featured on this app note…
http://www.seoulsemicon.com/_upload/Goods_Spec/[SPEC]SMJQ-XC95W4PX_Rev1.0.pdf
 

ronsimpson

Well-Known Member
Most Helpful Member
Before you put effort into this part, can you get the part?

Because as you know, floating copper pours on PCBs generate all kinds of noise problems?
A piece of copper does not generate noise. Maybe thermal noise. "all kinds of noise must include rap-music" lol
The copper might conduct noise from one place like your micro to another place.
‘floating’ pad
Most likely this floating pad is not connected to anything inside the IC. Does not mead you can't connect it to ground, or supply. It probably does not say you have to leave it floating. (they left it floating)
 

Flyback

Well-Known Member
Before you put effort into this part, can you get the part?
Yes, our Far Eastern buyer contact got us 1000 of them.
We put them on PCBs......some of them work some dont.....its the micro that doesnt respond to dali signals that worries us...though some do , some dont...we wonder if its noise from the DT3007Bs thermal pad which we left floating.
 

Flyback

Well-Known Member
Thanks,

Page 21 of the DT3001B datasheet says that the thermal pad should not be connected to any electrical node. Ive just found the DT3001B datasheet. DT3001B looks to be a sister chip of DT3007B.

DT3001B datasheet
http://www.seoulsemicon.com/_upload/Goods_Spec/Acrich2-Applicationnote.pdf

…maybe we could connect to gnd via a 100k resistor?

This is easy to fix. Wire and solder. Give it a try.
Thanks,,problem is we've already had 1000 PCBs made up with it floating...and the thermal copper is on the base of the PCB...we cannot add a wire there as it would rise the PCB off the heatsink on to which it is mounted.
A piece of copper does not generate noise.
Thanks, very true, but does a floating piece of copper act like a Yagi antenna and re-radiate noise all over the PCB?
 

ronsimpson

Well-Known Member
Most Helpful Member
gnd via a 100k resistor?
A 100k resistor will not conduct much current.

I think this "NC heatsink" is just like "NC pins". In most cases they are really not connected inside. Many people do not connect the pins because they are "NC". I found I can connect the NC pins to ground to help the ground plane.

What happens when you connect the heat sink to ground?
 

Flyback

Well-Known Member
What happens when you connect the heat sink to ground?
..Knowing our luck, probably nothing at first, but then two weeks after shipment, the entire batch of 1000 comes back failed-in-field due to some leakage current flowing from pin to themal pad.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top