Hello,
I'm using TUSB2036VFR - Full speed (12Mbps) USB 2.0 Hub controller in one of my projects. Here hub and downstream ports were detected but unable to see the clock frequency continuously at XTAL pins of hub. I observed the XTAL pins behavior using oscilloscope as described.
When hub being powered on was able to see 6Mhz clock at XTAL pins for a second and it goes flat (0V). After one or two second was able to see clock again for 3 seconds max and goes flat (0V). During this event hub and downstream ports detected. I also validated the same on 2 more same devices and the response was same.
Hub Configuration
Vcc = 3V3
RST# = with RC delay of 1ms (10k and 0.1uF) in schematics R146 was mentioned as resistor but it is a capacitor.
Mode = Low
BUSPWR# = High (Self powered)
Now, i just want to understand that is this a normal behavior or crystal 6Mhz should be continuous always?. Because clock in general will always be continuous. Attached here some reference images of my schematics, 6Mhx clock and flat signal both at XTAL pins. And one more observation was done, when i pull low the RST# was able to see continuous clock but hub and downstream not detected.
