Datasheet

DocID025644 Rev 3 79/135
STM32F401xD STM32F401xE Electrical characteristics
114
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
.
Note: For information on selecting the crystal, 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
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 38. 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).
Note: For information on selecting the crystal, refer to the application note AN2867 “Oscillator
design guide for ST microcontrollers” available from the ST website www.st.com.
Table 38. LSE oscillator characteristics (f
LSE
= 32.768 kHz)
(1)
1. Guaranteed by design, not tested in production.
Symbol Parameter Conditions Min Typ Max Unit
R
F
Feedback resistor - 18.4 - MΩ
I
DD
LSE current consumption - - 1 µA
G
m
_crit_max Maximum critical crystal g
m
Startup - - 0.56 µA/V
t
SU(LSE)
(2)
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 guaranteed by characterization and not tested in
production. It 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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