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Anik , 01-28-2026, 06:14 PM

Hi,
I recently designed a board using the ASM1184e PCIe switch with CM5. Power is from USB-C PD 20V/5A. Power rails (3.3V / 5V / 12V) look stable and are designed to be high-current capable.

Issue: CM5 detects the NVMe SSD and HDDs, works at first, but after some time the drives drop/disconnect randomly.

What I tested: I don’t have a differential probe. I used a Kingst LA2016 with analyzer GND connected to board GND, and probed CLK+ and CLK- with two channels. Using Custom I/O (Vth ~0.25–0.30V) I see a stable ~100MHz clock at ASM1184e input and also at the slot outputs (I know this is not a true differential measurement).

Sperate problem: The 1.2V regulator overheating maybe (65C). I peaked one which capable 2A and ASM1184 need 800mA max. But voltage is stable around 1.18v.

Design files and datasheets are provided, Please kindly check and let me know how can I test more with it.

Thanks!

Anik , 01-28-2026, 06:18 PM

I tried to force the PCIe gen1, but same problem.
Tried with bypass and PLL mode also enabled the clock termination on ASM1184e. But same issue.
May it caused by signal integrity issue? I am doing PCIe routing for the first time.
I made the stack up from JLC stack up tool and used Coplanner differential.

Anik , 01-28-2026, 07:20 PM

Anik , 01-28-2026, 07:22 PM

QDrives , 01-30-2026, 05:00 PM

Just because a regulator is spec'd for 2A, does not mean it can handle the 2A continuedly without thermal management.
Sleep mode?

Anik , 01-30-2026, 05:05 PM

ASM1184 need maybe 780mA max. And I am regulating 5V to 1.2V, maybe it causing heat for a large voltage drop? Otherwise 780mA is not too high for 2A capacity, no?
Sleep mode, what you meant? Did you mentioning the PCIe driver entering in sleep mode? But SSD, HDD dropping in random time. Like when I am going to copy a file from one drive to another.

Anik , 01-30-2026, 05:07 PM

Please check the layout also. I put all the PCIe and high speed lanes on the bottom side.
SIG (Ethernet, HDMI)
GND
PWR/Sig
PWR/Sig
GND
SIG (PCIe, Ethernet, SATA, HDMI)

QDrives , 01-30-2026, 05:07 PM

So 3.8V * 780mA = ~**3W**

Anik , 01-30-2026, 05:15 PM

Yes its a big drop and the IC temperature goes up to about 65 °C. Output voltage stays steady when I measure it. Do you think, the LDO could be the root cause here? If yes, what checks would you recommend to confirm (dropout/thermal shutdown/current limit)?

QDrives , 01-30-2026, 09:53 PM

Can you still reach the ASM1184 through I²C?

Anik , 01-31-2026, 04:42 AM

I2C/SMBus is only for the EEPROM. No connection with CM5

QDrives , 02-01-2026, 01:32 AM

Does the CM5 still see it when it 'stops'?

Anik , 02-01-2026, 04:50 AM

Yes, with I/O error.

QDrives , 02-01-2026, 08:39 PM

And what if you do the lspci command after the IO error?
Does it still see the switch?
In other words, is the error in the CM5 to the switch (including the switch) or from the switch to the rest?

Robert Feranec , 02-02-2026, 04:14 PM

i would try to run long run test on the SSD (I used to use passmark: https://www.passmark.com/products/burnintest/download.php?srsltid=AfmBOoo6KofGJZ1-Ic83zYc2oZyII_ulHfhTC4FdPzO4HCmsPpmU7ZAe ... but you can also make a script and keep reading a file in a loop or something simple) just to find out if it is randomly crashing or something else is happening. If it would be crashing, I would probably start with power and also double check the real speed and compare it with expected speed.

Anik , 02-02-2026, 06:20 PM

I will update you after those testing. Let me try.
Thanks for your helps.