shaiko
Advanced Member level 5
I often see PCB schematics that use single ended clocks with 50 Ohm parallel termination resistors at the Rx end.
The clock buffers are generally 3.3V LVCMOS.
When reading the datasheet of these crystal oscillators I often find the maximum current rating to be around 10mA.
However, if we divide 3.3 by 50 we get 70mA of current conssumption on the termination resistor.
My questions are:
1.Why doesn't the crystal oscillator burn out ?
2.How does the Rx buffer recognize valid logic '1' if the clock's buffer cannot drive enough current to get it to 3.3V ?
The clock buffers are generally 3.3V LVCMOS.
When reading the datasheet of these crystal oscillators I often find the maximum current rating to be around 10mA.
However, if we divide 3.3 by 50 we get 70mA of current conssumption on the termination resistor.
My questions are:
1.Why doesn't the crystal oscillator burn out ?
2.How does the Rx buffer recognize valid logic '1' if the clock's buffer cannot drive enough current to get it to 3.3V ?