CD00161566 Datasheet, PDF (53/105 Pages) STMicroelectronics – nullMedium-density performance line ARM-based 32-bit MCU

STM32F103x8, STM32F103xB
Electrical characteristics
Table 22. HSE 4-16 MHz oscillator characteristics^{(1) (2)}
Symbol
Parameter
Conditions
Min Typ Max Unit
f_{OSC_IN} Oscillator frequency
4
R_F Feedback resistor
-
Recommended load capacitance
C
versus equivalent serial
resistance of the crystal (R_S)⁽³⁾
R_S = 30
-
i₂
HSE driving current
V_DD = 3.3 V, V_IN = V_SS
with 30 pF load
-
8
16 MHz
200 -
k
30
-
pF
-
1 mA
g_m Oscillator transconductance
t_SU(HSE(4) startup time
Startup
25
-
V_DD is stabilized
-
2
- mA/V
-
ms
1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
2. Based on characterization, not tested in production.
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.
4.
ot^Ss^Uc⁽i^Hlla^SEtio⁾ nis
the startup
is reached.
time
This
measured from the moment it is enabled (by software) to
value is measured for a standard crystal resonator and it
a stabilized 8 MHz
can vary significantly
with the crystal manufacturer
For C_L1 and C_L2, it is recommended to use high-quality external ceramic capacitors in the
5 pF to 25 pF range (typ.), designed for high-frequency applications, and selected to match
the requirements of the crystal or resonator (see Figure 24). C_L1 and C_L2 are usually the
same size. The crystal manufacturer typically specifies a load capacitance which is the
series combination of C_L1 and C_L2. PCB and MCU pin capacitance must be included (10 pF
can be used as a rough estimate of the combined pin and board capacitance) when sizing
C_L1 and C_L2. Refer to the application note AN2867 “Oscillator design guide for ST
microcontrollers” available from the ST website www.st.com.
Figure 24. Typical application with an 8 MHz crystal
Resonator with
integrated capacitors
CL1
8 MH z
resonator
OSC_IN
RF
Bias
controlled
gain
fH_{S E}
CL2
REXT(1)
OSC_OU T
STM32F103xx
ai14145
1. R_EXT value depends on the crystal characteristics.
Low-speed external clock generated from a crystal/ceramic resonator
The low-speed external (LSE) clock can be supplied with a 32.768 kHz crystal/ceramic
resonator oscillator. All the information given in this paragraph are based on
characterization results obtained with typical external components specified in Table 23. 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).
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