Can USB1 in high speed mode working with 12MHz system clock in LPC55S28 controller?

[rahulshah]

Hi,

In our design it is required to use USB1 in high speed mode with 12MHz system clock.

So is USB1 in High-speed mode should work with 12MHz system clock? 12MHz system clock derived from FRO_12M.

Also in our design 12MHz crystal connected on XTAL32M for USB1-PHY clock.

So this solution should work or not? I have tested with different system clock as below and found following results.

system clock	derived from	USB1 High speed status
12 MHz	FRO_12M	Not working
16 MHz	FRO_96M	Not working
19.2 MHz	FRO_96M	Not working
24 MHz	FRO_96M	Not working
32 MHz	FRO_96M	working
48 MHz	FRO_96M	working
96 MHz	FRO_96M	working
150MHz	PLL150M	working
50MHz	PLL150M	working
37.5MHz	PLL150M	working
30MHz	PLL150M	not working

Regards,

Rahul Shah

[ZhangJennie]

USB1 must work with external crystal osc. internal osc is not for USB1.

see below:

Initial configuration of the USB1_PHY:
• Clocks:
– The XO32M crystal oscillator and must be powered up and configured to one of the
supported USB1_PHY reference clock frequencies of 16 MHz, 19.2 MHz, 20 MHz,
24 MHz or 32 MHz. Set the ENABLE_USB_HS_CLK_OUT bit of the
XO32M_CTRL register to enable the XO32M clock output to the USB1_PHY. See
Section 11.5.5.
– Enable the 32k_osc clock to provide the 32 kHz clock to the USB1_PHY.
– Set USB1_PHY in AHBCLKCTRL2, to enable clock to the USB1_PHY’s APB
register interface

Best Regards

Jun Zhang

[rahulshah]

Hi Jun Zhang,

Thanks for your reply.

So i have used and SDK example code "SDK_2.8.0_LPCXpresso55S28\boards\lpcxpresso55s28\usb_examples\usb_device_hid_generic\bm".

In that default system clock is 150MHz, and with LPC55S28 EVM kit USB1 as high speed works fine with above example code. 

Now if i change system clock to 12MHZ by using "BOARD_BootClockFRO12M" function in above example code, then USB1 as High-speed not working.

Note : with both usecase (12MHz and 150MHz system clock)16MHz crystal is connected to "XTAL32M" and USB1_PHY takes clock from that crystal.

Please find clock configuration image for 12MHz and 150MHz .

Regards,

Rahul Shah