Datasheet
Electrical characteristics STM32L071xx
80/144 DS10690 Rev 6
High-speed external clock generated from a crystal/ceramic resonator
The high-speed external (HSE) clock can be supplied with a 1 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 44. 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).
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 22). 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 22. HSE oscillator circuit diagram
Table 44. HSE oscillator characteristics
(1)
1. Guaranteed by design.
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 - ms
OSC_OUT
OSC_IN
f
HSE
to core
C
L1
C
L2
R
F
STM32
Resonator
Consumption
control
g
m
R
m
C
m
L
m
C
O
Resonator
ai18235b
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