Datasheet

Electrical characteristics STM32H743xI
118/226 DocID030538 Rev 3
High-speed external clock generated from a crystal/ceramic resonator
The high-speed external (HSE) clock can be supplied with a 4 to 48 MHz crystal/ceramic
resonator oscillator. All the information given in this paragraph are based on
characterization results obtained with typical external components specified in Table 43. In
the application, the resonator and the load c
apacitors have to be placed as close as
possible to the oscillator pins in order to minimize output distortion and startup stabilization
time. Refer to the crystal resonator manufacturer for more details on the resonator
characteristics (frequency, package, accuracy).
For C
L1
and C
L2
, it is recommended to use high-quality external ceramic capacitors in the
5 pF to 25 pF range (typical), designed for high-freq
uency applications, and selected to
match the requirements of the crystal or resonator (see Figure 18). C
L1
and C
L2
are usually
the same size. The crystal manufac
turer typically specifies a load capacitance which is the
series combination of C
L1
and C
L2
. The PCB and MCU pin capacitance must be included
(10 pF can be used as a rough estimate of the combined pin and board capacitance) when
sizing C
L1
and C
L2
.
Note: For information on selecting the c
rystal, refer to the application note AN2867 “Oscillator
design guide for ST microcontrollers” available from the ST website www.st.com.
Table 43. 4-48 MHz HSE oscillator characteristics
(1)
Symbol Parameter
Operating
conditions
(2)
Min Typ Max Unit
F Oscillator frequency - 4 - 48 MHz
R
F
Feedback resistor - - 200 - k
I
DD(HSE)
HSE current consumption
During startup
(3)
-- 4
mA
V
DD
=3 V, Rm=30 
C
L
=10pF@4MHz
-0.35 -
V
DD
=3 V, Rm=30 
C
L
=10 pF at 8 MHz
-0.40 -
V
DD
=3 V, Rm=30 
C
L
=10 pF at 16 MHz
-0.45 -
V
DD
=3 V, Rm=30 
C
L
=10 pF at 32 MHz
-0.65 -
V
DD
=3 V, Rm=30 
C
L
=10 pF at 48 MHz
-0.95 -
Gm
critmax
Maximum critical crystal gm Startup - - 1.5 mA/V
t
SU
(4)
Start-up time V
DD
is stabilized - 2 - ms
1. Guaranteed by design.
2. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
3. This consumption level occurs during the first 2/3 of the t
SU(HSE)
startup time.
4. t
SU(HSE)
is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz oscillation is
reached. This value is measured for a standard crystal resonator and it can vary significantly with the crystal manufacturer.
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