STM32F103XC Datasheet, PDF (54/118 Pages) STMicroelectronics – Performance line, ARM-based 32-bit MCU with up to 512 KB Flash, USB, CAN, 11 timers, 3 ADCs and 13 communication interfaces

Electrical characteristics
STM32F103xC, STM32F103xD, STM32F103xE
Low-speed external clock
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).
Table 23. LSE oscillator characteristics (f_LSE = 32.768 kHz)
Symbol
Parameter
Conditions
Min Typ Max Unit
R_F
Feedback resistor
5
MΩ
C_L1
Recommended load capacitance
versus equivalent serial
C_L2
resistance of the crystal (R_S)⁽¹⁾
R_S = 30 kΩ
15 pF
I₂
LSE driving current
V_DD = 3.3 V
V_IN = V_SS
1.4 µA
g_m
Oscillator Transconductance
t_SU(LSE)(2) startup time
5
V_DD is stabilized
3
µA/V
s
1. The oscillator selection can be optimized in terms of supply current using an high quality resonator with
small R_S value for example MSIV-TIN32.768kHz. Refer to crystal manufacturer for more details
2. t_SU(LSE) is the startup time measured from the moment it is enabled (by software) to a stabilized 32.768
kHz oscillation is reached. This value is measured for a standard crystal resonator and it can vary
significantly with the crystal manufacturer
Figure 21. Typical application with a 32.768 kHz crystal
Resonator with
integrated capacitors
CL1
32.768 kH z
resonator
CL2
OSC32_IN
RF
OSC32_OU T
Bias
controlled
gain
fLSE
STM32F103xx
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