External Source (Hse Bypass); External Crystal/Ceramic Resonator (Hse Crystal) - ST STM32F10 Series Application Note

Clocks
2.1.1

External source (HSE bypass)

In this mode, an external clock source must be provided. It can have a frequency of up to:
●
24 MHz for STM32F100xx value line devices
●
25 MHz for STM32F101xx, STM32F102xx and STM32F103xx devices
●
50 MHz for connectivity line devices
The external clock signal (square, sine or triangle) with a duty cycle of about 50%, has to
drive the OSC_IN pin while the OSC_OUT pin must be left in the high impedance state (see
Figure 7
2.1.2

External crystal/ceramic resonator (HSE crystal)

The external oscillator frequency ranges from:
● 4 to 16 MHz on STM32F101xx, STM32F102xx and STM32F103xx devices
●
4 to 24 MHz for STM32F100xx value line devices
● 3 to 25 MHz on connectivity line devices
The external oscillator has the advantage of producing a very accurate rate on the main
clock. The associated hardware configuration is shown in
The resonator and the load capacitors have to be connected as close as possible to the
oscillator pins in order to minimize output distortion and startup stabilization time. The load
capacitance values must be adjusted according to the selected oscillator.
For C and C
L1
25 pF range (typ.), designed for high-frequency applications and selected to meet the
requirements of the crystal or resonator. C
crystal manufacturer typically specifies a load capacitance that is the series combination of
C and C
L1
C (10 pF can be used as a rough estimate of the combined pin and board capacitance).
L2
Refer to the electrical characteristics sections in the datasheet of your product for more
details.
12/28
and Figure 6).
it is recommended to use high-quality ceramic capacitors in the 5 pF-to-
L2
. The PCB and MCU pin capacitances must be included when sizing C
L2
and C
L1 L2,
Doc ID 13675 Rev 7
Figure 7.
are usually the same value. The
AN2586
and
L1