Lse Osc Clock; Figure 17. Lse External Clock; Figure 18. Lse Crystal/Ceramic Resonators - ST STM32F4 Series Application Note

AN4488
6.2

LSE OSC clock

The low-speed external clock signal (LSE) can be generated from two possible clock
sources:
•
LSE user external clock (see
•
LSE external crystal/ceramic resonator (see

Figure 17. LSE external clock

1. "LSE crystal/ceramic resonators" figure:
To avoid exceeding the maximum value of C
resonator with a load capacitance C
2. "LSE external clock" and "LSE crystal/ceramic resonators" figures:
OSC32_IN and OSC32_OUT pins can be used also as GPIO, but it is recommended not to use them as
both RTC and GPIO pins in the same application.
3. "LSE crystal/ceramic resonators" figure:
The value of R
optimal. To fine tube R
and electrical characteristics sections in the datasheet of your product for more details.
Figure
≤
7 pF. Never use a resonator with a load capacitance of 12.5 pF.
L
depends on the crystal characteristics. A 0 Ω resistor would work but would not be
EXT
value, refer to AN2867 - Oscillator design guide for ST microcontrollers
S
AN4488 Rev 7
17)
Figure 18)
Figure 18. LSE crystal/ceramic
and C (15 pF) it is strongly recommended to use a
L1 L2
resonators
(Table
Clocks
2)
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