Datasheet

Electrical characteristics STM32F745xx STM32F746xx
122/227 DocID027590 Rev 4
5.3.9 External clock source characteristics
High-speed external user clock generated from an external source
In bypass mode the HSE 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 30.
The characteristics given in Table 37 result from tests performed using an high-speed
external clock source, and under ambient temperature and supply voltage conditions
summarized in
Table 17.
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 31.
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.
Table 37. High-speed external user clock characteristics
Symbol Parameter Conditions Min Typ Max Unit
f
HSE_ext
External user clock source
frequency
(1)
-
1-50MHz
V
HSEH
OSC_IN input pin high level voltage 0.7V
DD
-V
DD
V
V
HSEL
OSC_IN input pin low level voltage V
SS
-0.3V
DD
t
w(HSE)
t
w(HSE)
OSC_IN high or low time
(1)
1. Guaranteed by design.
5--
ns
t
r(HSE)
t
f(HSE)
OSC_IN rise or fall time
(1)
--10
C
in(HSE)
OSC_IN input capacitance
(1)
--5-pF
DuCy
(HSE)
Duty cycle - 45 - 55 %
I
L
OSC_IN Input leakage current V
SS
≤ V
IN
≤ V
DD
--±1µA
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