Datasheet

DS9118 Rev 14 79/149
STM32F303xB STM32F303xC Electrical characteristics
125
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 design
simulation results obtained with typical external components specified in
Table 43. 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 43. LSE oscillator characteristics (f
LSE
= 32.768 kHz)
Symbol Parameter Conditions
(1)
Min
(2)
Typ Max
(2)
Unit
I
DD
LSE current consumption
LSEDRV[1:0]=00
lower driving capability
-0.50.9
µA
LSEDRV[1:0]=10
medium low driving capability
--1
LSEDRV[1:0]=01
medium high driving capability
--1.3
LSEDRV[1:0]=11
higher driving capability
--1.6
g
m
Oscillator
transconductance
LSEDRV[1:0]=00
lower driving capability
5--
µA/V
LSEDRV[1:0]=10
medium low driving capability
8--
LSEDRV[1:0]=01
medium high driving capability
15 - -
LSEDRV[1:0]=11
higher driving capability
25 - -
t
SU(LSE)
(3)
Startup time V
DD
is stabilized - 2 - s
1. Refer to the note and caution paragraphs below the table, and to the application note AN2867 “Oscillator design guide for
ST microcontrollers”.
2. Guaranteed by design.
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.
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