ST STM32F103x6 Manual page 24

Electrical characteristics
Low-speed external clock
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
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 18.
Symbol
R
F
C
L1
C
L2
I
2
g
m
t
SU(LSE)
1. The oscillator selection can be optimized in terms of supply current using an high quality resonator with
small R
2. t
SU(LSE)
kHz oscillation is reached. This value is measured for a standard crystal resonator and it can vary
significantly with the crystal manufacturer
Figure 14. Typical application with a 32.768 kHz crystal
Resonator with
integrated capacitors
36/67
LSE oscillator characteristics (f
Parameter
Feedback resistor
Recommended load capacitance
versus equivalent serial
resistance of the crystal (R
LSE driving current
Oscillator Transconductance
(2)
startup time
value for example MSIV-TIN32.768kHz. Refer to crystal manufacturer for more details
S
is the startup time measured from the moment it is enabled (by software) to a stabilized 32.768
C L1
32.768 kH z
resonator
C L2
= 32.768 kHz)
LSE
Conditions
R = 30 kΩ
S
(1)
)
S
V = 3.3 V
DD
V = V
IN
V is stabilized
SS
OSC32_IN
Bias
controlled
R F
gain
OSC32_OU T
STM32F103xx
Table 18. In the application,
Min Typ
5
SS
5
3
f LSE
STM32F103xx
Max Unit
MΩ
15 pF
1.4 µA
µA/V
s
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