Datasheet

Electrical characteristics STM32L100C6, STM32L100R8/RB
62/102 DocID024295 Rev 1
Figure 12. HSE oscillator circuit diagram
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 27. 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 27. LSE oscillator characteristics (f
LSE
= 32.768 kHz)
(1)
1. Based on characterization, not tested in production.
Symbol Parameter Conditions Min Typ Max Unit
f
LSE
Low speed external oscillator
frequency
32.768 kHz
R
F
Feedback resistor 1.2 MΩ
C
(2)
2. Refer to the note and caution paragraphs below the table, and to the application note AN2867 “Oscillator
design guide for ST microcontrollers”.
Recommended load capacitance
versus equivalent serial
resistance of the crystal (R
S
)
(3)
3. 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;
R
S
= 30 kΩ 8pF
I
LSE
LSE driving current V
DD
= 3.3 V, V
IN
= V
SS
1.1 µA
I
DD (LSE)
LSE oscillator current
consumption
V
DD
= 1.8 V 450
nAV
DD
= 3.0 V 600
V
DD
= 3.6V 750
g
m
Oscillator transconductance 3 µA/V
t
SU(LSE)
(4)
4. 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.
Startup time V
DD
is stabilized 1 s
/3#?/54
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F
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