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| * | | external crystal problem
I have a problem with a lpc935 processor running at 3,3 Volt with an external HC49 crystal of 3.6864 MHz (drive level < 0,5 mW). The problem is that the amplitude of the XTAL2 signal is very low (1,54 Volt top-top sine wave using 15 pF shunt capacitors) while you expect around 3,1 Volt. The processor doesn''t run well then.
In Philips application note AN10289 I found that the internal impedance of the internal amplifier between XTAL1 and XTAL2 is about 2 kohm to 5 kohm which is (in my opinion) too low to drive the XTAL2 level to
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19-11-2004 3:31
Views: 2196 |
proodink |
| | | RE: external crystal problem
Hello there,
I haven''t heard of this problem being referred to with these micro''s before but felt I could offer something to the discussion.
1) In my understanding the port mode of the P3 pins are ignored when configured as a XTAL oscillator.
2) I doubt that I have seen a micro drive rail-to-rail and would expect such drive to be excessive (and potentially damaging). I would be looking for a drive that was distortion free and amplitude stable.
3) Your crystal may be more specific in it''s drive requirements than most and therefore trying the
... more (see whole posting)
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21-11-2004 16:26
Views: 2195 |
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