Datasheet

STM32F101xF, STM32F101xG Electrical characteristics
Doc ID 17143 Rev 2 53/108
Figure 19. 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 Tabl e 2 4 . 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).
ai14128b
OSC_OUT
OSC_IN
f
HSE
C
L1
R
F
STM32F10xxx
8 MHz
resonator
Resonator with
integrated capacitors
Bias
controlled
gain
R
EXT
(1)
C
L2
Table 24. LSE oscillator characteristics (f
LSE
= 32.768 kHz)
(1) (2)
Symbol Parameter Conditions Min Typ Max Unit
R
F
Feedback resistor 5 M
C
Recommended load capacitance
versus equivalent serial
resistance of the crystal (R
S
)
R
S
= 30 K 15 pF
I
2
LSE driving current
V
DD
= 3.3 V
V
IN
= V
SS
1.4 µA
g
m
Oscillator transconductance 5 µA/V
t
SU(LSE)
(3)
Startup time
V
DD
is
stabilized
T
A
= 50 °C 1.5
s
T
A
= 25 °C 2.5
T
A
= 10 °C 4
T
A
= 0 °C 6
T
A
= -10 °C 10
T
A
= -20 °C 17
T
A
= -30 °C 32
T
A
= -40 °C 60
1. Based on characterization, not tested in production.
2. Refer to the note and caution paragraphs below the table, and to the application note AN2867 “Oscillator design guide for
ST microcontrollers”.
3. 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 and it can vary significantly with the crystal manufacturer