2015-06-09 08:24 AM
Hello,
I would like to clock RTC with external clocking signal. The problem is, I have 10MHz TTL 0-5V signal at disposal but pins OSC_IN and OSC_OUT have TC pin structure (standart 3.3V I/O). I cannot simply reduce voltage by a resistor divider. While the diviter works fine with a direct current, it does not give expected result with 10MHz TTL signal (I am reading noise on oscilloscope). I read somewhere that parasitic capacitance on resistors can spoil high frequency signals.My question is either: 1) cannot I simply use the 0-5 TTL signal ? 2) how do I reduce voltage of high frequency signal without spoiling its shape significantly ? #rtc #stm32l1 #hse2015-06-09 09:29 AM
Use a 5 Volt tolerant part, like SN74LVC1G125 to level translate the part. If you can live with some load on the 5 Volt clock line, you can also use a well designed resistive divider.
2015-06-09 09:38 AM