Table 37. Lse Oscillator Characteristics; Figure 17. Typical Application With An 8 Mhz Crystal - STMicroelectronics STM32F042F4 Manual

STM32F042x4 STM32F042x6
1. R value depends on the crystal characteristics.
EXT
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
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 37. LSE oscillator characteristics (f
Symbol Parameter
I LSE current consumption
DD
Oscillator
g
m
transconductance
(3)
t Startup time
SU(LSE)
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 is the startup time measured from the moment it is enabled (by software) to a stabilized 32.768 kHz oscillation is
SU(LSE)
reached. This value is measured for a standard crystal and it can vary significantly with the crystal manufacturer

Figure 17. Typical application with an 8 MHz crystal

Conditions
low drive capability
medium-low drive capability
medium-high drive capability
high drive capability
low drive capability
medium-low drive capability
medium-high drive capability
high drive capability
V
DDIOx
DocID025832 Rev 5
37. In the application, the
Table
= 32.768 kHz)
LSE
(1)
is stabilized
Electrical characteristics
(2) (2)
Min Typ Max
- 0.5 0.9
- - 1
- - 1.3
- - 1.6
5 - -
8 - -
15 - -
25 - -
- 2 -
63/117
Unit
µA
µA/V
s
89