BOOT FAILURE IMX6 Custom Board

[summertanks]

I have designed and built a custom imx6 board. Design is similar to the reference diagram. The power supply is running off a NXP PF1510. The device is driven of the USB power rail (5.0V, stable supply). USB_OTG1 is connected to USB TypeA connector.

• All the power rail voltages from PMIC on power up are good (+/- 2%).
• RESETMCU on the PMIC is good (3.3V)
• POR_B either connected to PMIC RESETMCU or left floating is good (3.3V)
• SI analysis of the board done on altium doesn't indicate too much overshoot or undershoot.
• XTALs are ABS07-32.768KHZ-9-T and ASDMB-24.000MHZ-XY-T

Only OTG1 being used

Connected to USB Type A

BOOT MODE Selector switch, ONOFF Left floating. POR with two option - driven by PMIC / Left floating

https://i.stack.imgur.com/0bPEb.pngXTAL connected

THE PROBLEM STATEMENT

When connected to the PC (MAC/Linux/Windows) the device is not detected (should come up as HID).

• Tried do raw packet collection using wireshark, nothing there either.
• I do not think it is a Signal Integrity issue (impedance matching has been done, differential pair lengths checked, reference plane is good).
• Board quality looks good too, i have multiple prototypes but dosnt work on any - likely not a quality issue.
• Checked with different boot modes (serial connect BOOTMODE[1:0] = 01, boot from fuses BOOTMODE[1:0] = 00).
• I think either the imx6 is not booting or USB is not working - left floating POR_B is high (so that's good)and the USB differential is a straight circuit untouched and well shielded (i think).
• Since it is not detected as HID can't use Mfgtool2 for booting, so no UART.

Despite everything cannot get the device to be detected on USB. I would appreciated any ideas anyone can give.

Thank you (Do not have an oscilloscope)

[igorpadykov]

Hi Harkirat 

one can check board schematic using

Hardware Development Guide for the i.MX 6UltraLite Applications Processor

pay attention to 24MHz clock accuracy (it may affect usb detection) and power supplies

ripples (<5%). Try with several computers. Just for test one can prolong POR up to 1 sec.

Best regards
igor
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[summertanks]

Igor,

Thanks for your reply.

The voltage rails are
VBUS - 5.145V (PMIC supply)
SW1 - 1.389V
SW2 - 1.355V
SW3 - 3.340V
VLDO1 - 1.802V
VLDO2 - Unconnected
VLDO3 - 3.296
VSNVS - 3.041V
DDR_VREF - 0.676V

on power on with POR_B floating POR_B - 3.309V

Tried powering up the board with POR_B pulled down released after > 5 sec - No detection
Tried pulling down POR_B after 10 sec of PMIC power on (initially with POR_B floating) - no detection

XTAL

ABS07-32.768kHZ-9-T
ESR - 70kOhm
Load Cap - 9pF and board cap is 9pF +/- 0.1pF

ASDMB-24.000MHZ-XY-T
Stability +/- 10ppm (not checked)
Output load 10kOhm
Load Cap - 15pF
Board Cap 15pF (1%)
Deviation - 2.2M registor to GND for XTALI bias not externally adjustable

Q: Based on the schematic i have shared, are the board caps correct?

one can check board schematic using

Hardware Development Guide for the i.MX 6UltraLite Applications Processor

Done that.the only deviations are 

Since BOOT_MODE[1:0] have an on chip pulldown (Page 12) are not connected externally to GND at 00
Kept Floating
      USB_OTG1_ID - Type A connector not microusb
      USB_OTG1_OC
      USB_OTG_PWR

I am severely hampered due to lack of oscilloscope, short of that is there anything else i can try?

Again, any ideas are appreciated.

Regards,