Datasheet
DocID15274 Rev 10 49/108
STM32F105xx, STM32F107xx Electrical characteristics
107
Figure 15. Low-speed external clock source AC timing diagram
High-speed external clock generated from a crystal/ceramic resonator
The high-speed external (HSE) clock can be supplied with a 3 to 25 MHz crystal/ceramic
resonator oscillator. All the information given in this paragraph are based on
characterization results obtained with typical external components specified in Table 22. In
the application, the resonator and the load capacitors have to be placed as close as
possible to the oscillator pins in order to minimize output distortion and startup stabilization
time. Refer to the crystal resonator manufacturer for more details on the resonator
characteristics (frequency, package, accuracy).
Table 22. HSE 3-25 MHz oscillator characteristics
(1)
(2)
1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
2. Based on characterization, not tested in production.
Symbol Parameter Conditions Min Typ Max Unit
f
OSC_IN
Oscillator frequency - 3 25 MHz
R
F
Feedback resistor - - 200 - kΩ
C
Recommended load capacitance
versus equivalent serial
resistance of the crystal (R
S
)
(3)
3. The relatively low value of the RF resistor offers a good protection against issues resulting from use in a
humid environment, due to the induced leakage and the bias condition change. However, it is
recommended to take this point into account if the MCU is used in tough humidity conditions.
R
S
= 30 Ω - 30 - pF
i
2
HSE driving current
V
DD
= 3.3 V, V
IN
=V
SS
with 30 pF load
- - 1 mA
g
m
Oscillator transconductance Startup 25 - - mA/V
t
SU(HSE
(4)
4. t
SU(HSE)
is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz
oscillation is reached. This value is measured for a standard crystal resonator and it can vary significantly
with the crystal manufacturer
Startup time V
DD
is stabilized - 2 - ms
ai14140c
OSC32_IN
External
STM32F10xxx
clock source
V
LSEH
t
f(LSE)
t
W(LSE)
I
L
90%
10%
T
LSE
t
t
r(LSE)
t
W(LSE)
f
LSE_ext
V
LSEL
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