Recommended Oscillator for STM32F407

[schauhan112]

Posted on January 25, 2013 at 01:05

I have designed a custom board around STM32F407VET.  I am using 8 MHz external oscillator (ABRACON ABLS-8.000MHZ-B2-T) with 22 pf load capacitors (CL) and 220 ohm REXT.  When I probe OSC_IN or OSC_OUT pins using logic analyzer I see no oscillation.  I have tried various values of CL from 18 pf to 27 pf and REXT from 120 to 470 ohm with no success.  I measure the correct frequeny on STMF4 Discovery kit with my set up.  Since external oscillator is not working the microcontroller automatically switches to internal oscillator and I am able to program the board.  However, I would like to use the external oscillator as planned.  I would appreciate if someone can recommend oscillator part number, CL and REXT values that they have used in the past and are known to work with STM32F4xx series.

Thanks. 

[Tesla DeLorean]

Posted on January 25, 2013 at 03:33

The part starts with the HSI, it has to have the HSE enabled manually, do you have software on it doing that? The Discovery board has a 20pF crystal. The Abracon is 22pF, 80 Ohm ESR, most recommended by ST seem to be 20pF or less.

You could also try a 0 Ohm.

The lead length also needs to be very short. Perhaps you can provide a gerber fragment of the topology. Consider also the impact of scope probes to the circuit.

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/APPLICATION_NOTE/CD00221665.pdf

[Andrew Neil]

Posted on January 25, 2013 at 07:36

''I probe OSC_IN or OSC_OUT pins using logic analyzer''

 

You should be using an Oscilloscope to look at those - they are analogue signals!