Datasheet

DS12323 Rev 2 57/91
STM32L010F4/K4 Electrical characteristics
81
time. Refer to the crystal resonator manufacturer for more details on the resonator
characteristics (frequency, package, accuracy).
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 (seeFigure 16). 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 Oscillator design guide for STM8AF/AL/S and
STM32 microcontrollers (AN2867) available from the ST website www.st.com.
Figure 16. HSE oscillator circuit diagram
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 35. 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
Table 34. HSE oscillator characteristics
(1)
1. Guaranteed by design, not tested in production.
Symbol Parameter Conditions Min Typ Max Unit
f
OSC_IN
Oscillator frequency - 1 - 25 MHz
R
F
Feedback resistor - - 200 - kΩ
G
m
Maximum critical crystal
transconductance
Startup - - 700 µA/V
t
SU(HSE)
(2)
2. Guaranteed by characterization results. 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 - s
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