Other Parts Discussed in Thread: TUSB4020BPHPEVM
Hi!
I designed a custom PCB using the TUSB4020BI with an external OCXO oscillator but ran into a problem. This external oscillator (OH200-51003CF) is self powered with a 12V rail and I also have another 5V rail for the rest of the circuit (regulators and USB switching power).
If I power on the 5V rail after the 12V rail (or at the same time), downstream ports does not initialize and sometimes the upstream port also does not work. But, if I only power on the 5V rail before the 12V everything works ok.
Summay:
- Power on 5V rail after or at same time as 12V rail: Chip does not initialize
- Power on 12V rail after 5V rail: Chip initializes successfully
- Reset chip (GRSTZ pin) after a failed initialization: Chip initializes successfully
It seems that the TUSB4020BI fails to initialize when he's receiving a input clock of an external oscillator before it is powered on. My circuit is almost an exact replica of the TUSB4020BPHPEVM board, the only differences are the external oscillator and regulators.
Edit: Manage to find that when receiving XI from the oscillator without any other power rails, GRSTZ pin rises up to 1.7V. If this pin (and maybe others) have some voltage before power up the chip, Power-Up timing requirements are not satisfied.
