Electrical characteristics
STM32F302xx/STM32F303xx
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 41. 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 41. LSE oscillator characteristics (fLSE = 32.768 kHz)
Symbol
Parameter
Conditions(1)
Min(2)
Typ Max(2) Unit
LSEDRV[1:0]=00
lower driving capability
-
0.5
0.9
1
LSEDRV[1:0]=01
medium low driving capability
-
-
-
-
-
-
-
-
IDD
LSE current consumption
µA
LSEDRV[1:0]=10
medium high driving capability
1.3
1.6
-
LSEDRV[1:0]=11
higher driving capability
-
LSEDRV[1:0]=00
lower driving capability
5
8
15
LSEDRV[1:0]=01
medium low driving capability
-
Oscillator
transconductance
gm
µA/V
LSEDRV[1:0]=10
medium high driving capability
-
LSEDRV[1:0]=11
higher driving capability
25
-
-
-
-
(3)
tSU(LSE)
Startup time
VDD 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, not tested in production.
3. tSU(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
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.
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Doc ID 023353 Rev 5
STMICROELECTRONICS [ ST ]
