Crystal drive level for CY7C65632 | Cypress Semiconductor
Crystal drive level for CY7C65632
I reviewed the Guidelines on System Design doc for USB HX2VL families. We are using the CY7C65632. Section 3.2.1, Crystal Drive Level, isn't making sense to me. The required power level is extremely high, such that it's impossible to find small crystals which would work. Most small crystals have a max. drive level of 100 uW, and the Guide says 600 uW but then provides a formula to calculate the drive power. It's the formula which isn't making sense. Shouldn't the voltage Vx be the RMS, not the peak voltage? And why is the "2" outside the brackets?
Let's look at an example calculation, using typical values for crystals we're considering.
Vx = 3.36 V
Co = 7 pF
CL = 18 pF
R = 60 ohms
f = 12 MHz
Power from the formula is 2 * [pi * 12E6 * (7 + 18)E-12 * 3.36] ^ 2 * 60 = 1.2 mW. This is an absurdly high drive level! Is there an error in the formula?