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STM32F042x4 STM32F042x6
Electrical characteristics
89
Figure 17. Typical application with an 8 MHz crystal
1. R
EXT
value depends on the crystal characteristics.
Low-speed external clock generated from a crystal resonator
The low-speed external (LSE) clock can be supplied with a 32.768 kHz crystal resonator
oscillator. All the information given in this paragraph are based on design simulation results
obtained with typical external components specified in
. 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).
069
26&B,1
26&B287
5
)
%LDV
FRQWUROOHG
JDLQ
I
+6(
5
(;7
0+]
UHVRQDWRU
5HVRQDWRUZLWKLQWHJUDWHG
FDSDFLWRUV
&
/
&
/
Table 37. LSE oscillator characteristics (f
LSE
= 32.768 kHz)
Symbol
Parameter
Conditions
(1)
Min
Typ
Max
(2)
Unit
I
DD
LSE current consumption
low drive capability
-
0.5
0.9
µA
medium-low drive capability
-
-
1
medium-high drive capability
-
-
1.3
high drive capability
-
-
1.6
g
m
Oscillator
transconductance
low drive capability
5
-
-
µA/V
medium-low drive capability
8
-
-
medium-high drive capability
15
-
-
high drive capability
25
-
-
t
SU(LSE)
(3)
Startup time
V
DDIOx
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. 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
