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Electrical characteristics
High-speed external clock generated from a crystal/ceramic resonator
The high-speed external (HSE) clock can be supplied with a 4 to 32 MHz crystal/ceramic
resonator oscillator. All the information given in this paragraph are based on design
simulation results obtained with typical external components specified in
application, the resonator and the load capacitors 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).
Symbol
f
OSC_IN
R
F
I
DD
g
m
(4)
t
SU(HSE)
1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
2. Guaranteed by design, not tested in production.
3. This consumption level occurs during the first 2/3 of the t
4. t
SU(HSE)
oscillation is reached. This value is measured for a standard crystal resonator and it can vary significantly
with the crystal manufacturer
For C
and C
L1
5 pF to 20 pF range (Typ.), designed for high-frequency applications, and selected to match
the requirements of the crystal or resonator (see
same size. The crystal manufacturer typically specifies a load capacitance which is the
series combination of C
can be used as a rough estimate of the combined pin and board capacitance) when sizing
C
and C
L1
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.
54/102
Table 31. HSE oscillator characteristics
Parameter
Oscillator frequency
Feedback resistor
HSE current consumption
Oscillator transconductance
Startup time
is the startup time measured from the moment it is enabled (by software) to a stabilized 8 MHz
, it is recommended to use high-quality external ceramic capacitors in the
L2
and C
L1
.
L2
DocID026079 Rev 3
Conditions
-
-
During startup
V
= 1.8 V,
DD
Rm = 30 Ω,
CL = 10 pF@8 MHz
V
= 1.8 V,
DD
Rm = 45 Ω,
CL = 10 pF@8 MHz
V
= 1.8 V,
DD
Rm = 30 Ω,
CL = 5 pF@32 MHz
V
= 1.8 V,
DD
Rm = 30 Ω,
CL = 10 pF@32 MHz
V
= 1.8 V,
DD
Rm = 30 Ω,
CL = 20 pF@32 MHz
Startup
V
is stabilized
DD
SU(HSE)
Figure
. PCB and MCU pin capacitance must be included (10 pF
L2
Table
(1)
(2)
Min
Typ
4
8
-
200
(3)
-
-
0.4
-
0.5
-
0.8
-
1
-
1.5
10
-
-
2
startup time
15). C
and C
are usually the
L1
L2
STM32F038x6
31. In the
(2)
Max
Unit
32
MHz
-
kΩ
8.5
-
-
mA
-
-
-
-
mA/V
-
ms
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