Datasheet

DocID030538 Rev 3 117/226
STM32H743xI Electrical characteristics
196
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 58: I/O static characteristics. However, the
recommended clock input waveform
is shown in Figure 17.
Note: For information on selecting the crystal, refer to the application note AN2867 “Oscillator
design guide for ST microcontrollers” available from the ST website www.st.com.
Figure 17. Low-speed external clo
ck source AC timing diagram
Table 42. Low-speed external user clock characteristics
(1)
Symbol Parameter Conditions Min Typ Max Unit
f
LSE_ext
User external clock source frequency - - 32.768 1000 kHz
V
LSEH
OSC32_IN input pin high level voltage - 0.7 V
DDIOx
-V
DDIOx
V
V
LSEL
OSC32_IN input pin low level voltage - V
SS
-0.3 V
DDIOx
t
w(LSEH)
t
w(LSEL)
OSC32_IN high or low time - 250 - - ns
1. Guaranteed by design.
ai17529b
OSC32_IN
External
STM32
clock source
V
LSEH
t
f(LSE)
t
W(LSE)
I
L
90%
10%
T
LSE
t
t
r(LSE)
t
W(LSE)
f
LSE_ext
V
LSEL
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