[SI-LIST] Re: Noise coupling from TI's MSP430FR5728 MCU to TI's DS100BR210 repeater
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 16 Sep 2014 03:14:08 -0700
How thick is the power / ground cavity? What penetrates the cavity? Do
you have polygons that belong to different power rails overlapping each
other? Do you see that noise on the power rails? At the MPS430? On
any of its I/Os? Do you see the noise on the repeater power pins?
How carefully did you design your bypass network?
I tend to suspect that what you are seeing is noise from an internal
clock in the repeaters showing up as noise current impressed on an
excessive PDN Z11 and not noise from the MPS430. If that isn't it, then
I would look at the repeater input biasing. If I were you I would load
a test program that configures the repeaters and then puts the MPS30
into power down sleep. I would create a version that configures the
repeaters to sleep as well.
Steve
On 9/16/2014 2:44 AM, Jinhua Chen (Redacted sender jhchen0710@xxxxxxxxx
for DMARC) wrote:
> Hi, expert
>
> Any one has experience with TI's MSP430FR5728 MCU? I had a noise issue when
> it used to control 4 TI's DS100BR210 repeaters.
>
> The noise frequency is about 22 Mhz with amplitude of ~ 15 mV. The noise
> showed up in the input pins and output pins of DS100BR210 repeater when
> repeater is in idle (no signal inputs or outputs). DS100BR210 repeater is a
> high speed signal conditioner with TX emphasis and RX equalization.
> MSP430FR5728 MCU and DS100BR210 share the power plane and ground. The noise
> source is suspected from MCU. Repeater inputs were terminated to Vdd via 50
> ohms internally. I tried to isolate the power from MCU to repeater but it
> didn’t help. The other connection between MCU and repeater is the I2C bus. I
> can’t imagine that the I2C bus can bring the noise from MCU to repeater.
>
> This really puzzles me. My PCB board only has 5 active chips with one MCU and
> 4 repeaters. It is a simple board design. Anyone out there who experienced
> this? TI design engineers are welcome to contact me directly via email.
>
> Thanks!
>
> Jinhua Chen
>
>
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