Datasheet

Electrical characteristics STM32F091xB STM32F091xC
70/128 DocID026284 Rev 4
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
Table 40. 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).
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Table 40. LSE oscillator characteristics (f
LSE
= 32.768 kHz)
Symbol Parameter Conditions
(1)
Min
(2)
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
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