Posted on June 26, 2018 at 11:19Hi everyone,
I'm working on an STM32F1 platform. I'm using this crystal ABMM2-8.000MHZ-E2-T for the HSE setting.
I made of the calculation according to the application note AN2867:
According to the datasheet ABMM2-8.000MHZ-E2-T:
C0=7pF, ESR(max 8.0MHz)=72ohm, CL=18pF and F= 8.0MHz
And according to the datasheet (page 60/136) del STM32F103RF:
gm = 25mA/V
gmcrit = 4 * ESR * (2?F)^2 * (C0 + CL)^2 = 4 * 72 *(2 * pi * 8 * 10^6)^2 * (7*10^(-12) + 18 *10^(-12) )^2 = 0.0004547913708022 A/V = 0.4547913708022 mA/V
gain margin = gm/gmcrit = 25 / 0.4547913708022 = 54.97 > 5
But I don't know If I have to place a Rext or not. According to the AN2867: 'If the power dissipated in the crystal is higher than the value specified by the crystal manufacturer, the external resistor Rext becomes mandatory to avoid overdriving the crystal. If the power dissipated in the selected quartz is less than the drive level specified by the crystal
manufacturer, the insertion of Rext is not recommended and its value is then 0 ?.'
According to the datasheet ABMM2-8.000MHZ-E2-T:
DL (typ) = 100uWatts and DL(max) = 500uWatts
And where can I see the maximum power feed by the STM32F103 for the HSE? I was trying to see this value in the datasheet but I wasn't able to find it.
#stm32f1 #rext #hse
