OSC input start timing in HX2VL

[TeMa_2997106]

Are there any time restrictions from power-on to OSC oscillation start?

OSC oscillates after USBHUB (CY7C65642) power is turned on. Is this a problem?

Also, are there any restrictions on the waveform to be input to RESET? For example, is there a rise time specification? I'm wondering if the ramp up rate of the waveform affects the behavior of the HX2VL.

Thanks,
Tetsuo

[Takashi_O]

Hi @TeMa_2997106 ,

Thank you for posting into our community.

No, there is no issue having such the power sequence if POR(Power on Reset) is excecuted properly.
Reset pulse duration should be longer than 3us, and the POR should be applied at 5ms after that Power supply and clock source becomes stable.
RESET# is open-drain pin so There is no rise/fall time requirements for this pin.

Regards,

Takashi Onawa

[TeMa_2997106]

Takashi-san,

Thank you for your answer.
And I apologize for the delay in replying my comment.

Are there any POR requirements for this device?
It pulls up the RESET pin. There is no active external reset.
Are there any issues with this configuration?

Thanks,
Tetsuo

[Takashi_O]

Hi Matsubara-san,

RC delay generator is also OK but the time constant of your circuit looks too low. 
Normally, 100kohm with 0.1uF is recommended to secure enough #RESET release timing  as described in the datasheet.

Regards,

TakashiO

[Takashi_O · Accepted solution]

Hi Matsubara-san,

Sorry, the recommendation above is for HX2LP, not HX2VL.
For HX2VL, 10kohm with 1uF is recommended as described in the following guideline. Please find "3.7 Reset Circuit" in the document.
Guidelines on System Design Using Cypress’ USB 2.0 Hub (HX2VL)