Datasheet

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STM32F427xx STM32F429xx Electrical characteristics
198
Low-speed external user clock generated from an external source
In bypass mode the LSE oscillator is switched off and the input pin is a standard I/O. The
external clock signal has to respect the Table 56: I/O static characteristics. However, the
recommended clock input waveform is shown in Figure 28.
The characteristics given in Table 38 result from tests performed using an low-speed
external clock source, and under ambient temperature and supply voltage conditions
summarized in Table 17.
Figure 27. High-speed external clock source AC timing diagram
Table 38. Low-speed external user clock characteristics
Symbol Parameter Conditions Min Typ Max Unit
f
LSE_ext
User External clock source
frequency
(1)
- 32.768 1000 kHz
V
LSEH
OSC32_IN input pin high level
voltage
0.7V
DD
-V
DD
V
V
LSEL
OSC32_IN input pin low level voltage V
SS
-0.3V
DD
t
w(LSE)
t
f(LSE)
OSC32_IN high or low time
(1)
450 - -
ns
t
r(LSE)
t
f(LSE)
OSC32_IN rise or fall time
(1)
--50
C
in(LSE)
OSC32_IN input capacitance
(1)
-5-pF
DuCy
(LSE)
Duty cycle 30 - 70 %
I
L
OSC32_IN Input leakage current V
SS
≤V
IN
≤V
DD
--±1µA
1. Guaranteed by design.
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