Electrical characteristics
STM32F302xx/STM32F303xx
6.3.7
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 GPIO. The
external clock signal has to respect the I/O characteristics in Section 6.3.14. However, the
recommended clock input waveform is shown in Figure 14.
Table 38. High-speed external user clock characteristics
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
User external clock source
frequency(1)
fHSE_ext
1
8
32
MHz
VHSEH
VHSEL
tw(HSEH)
OSC_IN input pin high level voltage
OSC_IN input pin low level voltage
0.7VDD
VSS
-
-
VDD
V
0.3VDD
OSC_IN high or low time(1)
OSC_IN rise or fall time(1)
15
-
-
-
-
tw(HSEL)
ns
tr(HSE)
tf(HSE)
20
1. Guaranteed by design, not tested in production.
Figure 14. High-speed external clock source AC timing diagram
T
7ꢐ(3%(ꢑ
6
(3%(
ꢅꢄꢒ
ꢃꢄꢒ
6
(3%,
T
T
T
Rꢐ(3%ꢑ
T
7ꢐ(3%,ꢑ
Fꢐ(3%ꢑ
4
(3%
-3ꢃꢅꢉꢃꢀ6ꢉ
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