topic Re: Does the LPC4357 need a crystal for USB DFU? in LPC Microcontrollers

Does the LPC4357 need a crystal for USB DFU?

lpcware — Wed, 15 Jun 2016 18:35:36 GMT

Content originally posted in LPCWare by suckfish on Sat Sep 22 22:10:56 MST 2012
Hi,

I'm bringing up a board with a LPC4357 on it. Does it need a crystal for the DFU over USB0? (The docs don't say so, but high-speed USB devices normally have a crystal?)

On my board - Strapping for boot ISP via USART3 works fine. Strapping for boot DFU via USB0 doesn't seem to work (the host PC is completely unaware of the device)... So I'm crossing my fingers that it's a simple problem not a toasted board/chip...

Ralph.

Re: Does the LPC4357 need a crystal for USB DFU?

lpcware — Wed, 15 Jun 2016 18:35:37 GMT

Content originally posted in LPCWare by suckfish on Tue Sep 25 01:00:27 MST 2012
To answer my own question, it is documented in the user manual: "This boot mode requires that a 12 MHz external crystal is connected to the XTAL1/2 pins."

Not sure how I missed it before...

Now to solder the xtal to my board.

Re: Does the LPC4357 need a crystal for USB DFU?

lpcware — Wed, 15 Jun 2016 18:35:38 GMT

Content originally posted in LPCWare by bavarian on Tue Sep 25 02:18:22 MST 2012
Hello Ralph,

for full speed operation the internal 12MHz oscillator could be maybe precise enough (if trimmed correctly), but for high speed you need for sure an external crystal (DFU bootloading doesn't use high speed).
However, as it is not possible to always guarantee the accuracy of the IRC after power up, the USB DFU boot mode was based on the existence of an external crystal.

Best regards,
NXP Technical Support