[C5535] Confirm the power-up sequence with using USB function

1. if the DSP_LDO is disabled (DSP_LDO_EN = high) and an external regulator supplies power to the CPU Core (CVDD), the external reset signal (RESET) must be held asserted until all of the supply voltages reach their valid operating ranges.
2. If 32KHz Oscillator is used, then 2 second delay must to be allowed for oscillator to stabilize. This delayed is required once CVDDRTC is powered and before external reset is de-asserted. 
3. If the USB subsystem is used, the subsystem must be powered up in the following sequence:

Hi Vasanth,
Thank you for your response.
Please let me confirm my understanding and solution for usb power-up sequence.

[My understanding]
1.If customer would like to use the USB function, they need to be gated the voltage the USB_VBUS and USB_VDDA3P3 until power up the USB_LDO turns on.
2. The other USB power domains such as USB_VDDOSC and USB_VDDPLL need not follow this limitation.

Is my understanding correct?

[Solution for USB domain power-up]
Are the following schematics satisfied with USB domain power-up sequence?

*Schematic.1
3.3V(Source)-------FET(or Load　Switch)-------USB_VDDA3P3
                                     |
                          USB_LDO(1.3V)
*Schematic.2
USBBUS(5V)(source)------FET(or Load Switch)----------USB_VBUS
                                                   |
                                          USB_VDDA3P3(3.3V)

If you have any questions, please let me know.
Best regards.
kaka

Hi Kaka-san, 

A1. Yes, The voltages to USB_VDDA3P3 and USB_VBUS (as seen by the C55xx) needs to be gated until the USB_LDO turns ON (supplies USB_VDDA1P3 and USB_VDD1P3)

A2. Yes as per my understanding there is no limitation. Datasheet too doesn't  mention any such limitation.

With respect to your schematics, its not very clear can you please re-present this. 

Regards

 Vasanth

Hi Vasanth,

Thank you for your confirming. And I apologize for my poor explanation.
I summarized the solution for power sequence of USB domain in my previous post.

USB LDO is not active when the C5535 reboot from RTC-only mode.
Thus, customer need to wait for powering USB domain until USB LDO will be active.
Is my understanding correct?

So I think that the following sequence will be satisfied with this limitation.
1. Inset the FETs or Load switches in USB_VDDA3P3 line and VBUS line.
2. Gate the USB_VDDA3P3 line by USB_LDOO
i.e. Source is connected to 3.3V line for USB_VDDA3P3. The gate(or Enable pin) is connected to USB_LDOO. The drain is connected to USB_VDDA3P3 pin.
3. Gate the VBUS line on C5535 by USB_VDDA3P3
i.e. The source is connected to VBUS line from PC or AC adapter. The gate(or Enable pin) is connected to USB_VDDA3P3. The drain is connected to USB_VBUS pin.

Can we propose this solution to my customer?

I have two more questions for USB power sequence.
 1. Does customer application need to be satisfied this when it reboot the C5535 from RTC-only mode?

 2. Will the C5535 keep to be disabled the USB_LDOO when their system will wake-up from RTC-only mode and reboot except for USB or UART boot?
  *USB boot will be enabled the USB_LDOO in bootloader. So I would like to know whether this LDO will keep to be disabled by bootloader if customer use the other boot mode.

If you have any question, please let me know.
Best reagards.
Kaka

Hi Kaka-san,

This is been looked by right expert. Will reply on this soon.

Regards

Vasanth

Hi Kaka-san,

Just to update, we are still looking at this,  Will get back soon.

Regards

 Vasanth

Hi Vasanth,

Thank you for your updates.

I made the sequence block for c55x. please check this.

 8585.C5535 power sequence.xlsx

I also posted this to another E2E as below.

** I updated the attached file on 2015/8/27 18:44 JPN

Best regards.

Kaka