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USB Superspeed Peripherals

Anonymous
Not applicable

Hi,

I have an FX3 which is as follows:

VIO1 is 1V8

VIO2 is 1V8

VIO3 is VADJ

VIO4 is 1V8

VIO5 is VADJ

AVDD is 1V2

VDD is 1V2

U3TXVDDQ is 1V2

U3RXVDDQ is 1V2

CVDDQ is 1V8

U3VSSQ is GND

VBATT is connected to VBUS

When VADJ is connected to 1V8, everything is hunky-dory. But when VADJ is connected to 2V5, my 1V8 rail for VIO1, VIO2, VIO4 and CVDDQ is shifted up to 2V6.

I don't have any conflict between 1V8 and 2V5 I/O. And the fact that is raised above 2V5 means it is most likely from the 5V or the internally generated 3V3.

Does my power rail combination not possible, they are normally between the limits express in the datasheet.

Any help is welcome. Thanks.

Etienne

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1 Solution
alamandaa_16
Moderator
Moderator

Hi Etienne,

----Your design meets section 4 of FX3 Hardware design guidelines (AN70707), in this case your design works fine and no errors.

Regards,

Anil Srinivas.

View solution in original post

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9 Replies
alamandaa_16
Moderator
Moderator

Hello Etienne,

--Please share the power supply section of schematic.

Regards,

Anil Srinivas.

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Anonymous
Not applicable

This is how my FX3 is connected.

FX3_PowerSupply.png

I tried to replicate this power distribution to my development kit (CYUSB3KIT-001), I haven't see the problem.

The difference I can trace between the kit and my board is:

CTL2 (J7) & CTL3 (H7) connected to 1V8

CTL9 (H6) & CTL10 (K5) connected to GND

DQ21 (J1) as a 10K pull-up to 5V

I2S-MCLK (C4) as a 270R in serie with a pull-up at 2V5

VBUS connected to VBAT

FX3 is in the USB fallback state so most of the pins are Tristate.

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Anonymous
Not applicable

I removed the SPI Flash I had on my board and the 1V8 rail went to 3.2V (My SPI Flash was possibily the one clamping the rail).

I removed the FX3 to put in place one from another batch, same issue. I also cut the track that connect E10 to VBUS before soldering back the BGA, just in case.

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Anonymous
Not applicable

This is the power sequence for my 5V, 1V2, 1V8 and VADJ (2V5). It can be seen that the 1V8 is okay and start jumping to 3V.

181203_StartupPower_2.jpg

The moment the 1V8 rail start raising seems linked to the time when the POR release the RESET signal for the FX3.

181203_StartupPower_1.jpg

If I force the RESET to be always low, the 1V8 still raise but only to 2V1.

181203_StartupPower_3.jpg

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alamandaa_16
Moderator
Moderator

Hello Etienne Joly,

--Decoupling capacitors should be connect to the power pins, I think Decoupling capacitors are not connected in your schematic.

Please see the following image.

power supply decoupling capacitor.JPG

Regards,

Anil Srinivas.

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Anonymous
Not applicable

Here is the decoupling capacitors on my board. I tried to respect the AN70707 recommendations (Capacitors Placement and Routing), as I always do for my FX3 designs.

FX3_PowerSupply_Decoupling.png

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Anonymous
Not applicable

After further tests it seems that somehow the 1V8 regulator "Open" its output and let it floats somehow.

Here is the voltage at Startup, I put some code in the EEPROM for the FX3 to "work" on it, few seconds at startup:

181205_Startup_Flash_1.jpg

So the 1V8 is fine then once the FX3 as finished, the rail start to float. I also measured the current on my 1V8 rail. It is quite small and we can see that it reverses.

FX3_Startup_Current_0.png

This is the power supplies for the sake of completeness:

Board_PowerSupply.png

My current workaround is to add a small resistive load at the regulator output.

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alamandaa_16
Moderator
Moderator

Hello Etienne,

-Please share the complete schematic of your design.

Regards,

Anil Srinivas.

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alamandaa_16
Moderator
Moderator

Hi Etienne,

----Your design meets section 4 of FX3 Hardware design guidelines (AN70707), in this case your design works fine and no errors.

Regards,

Anil Srinivas.

View solution in original post

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