CD00237391 Datasheet, PDF (83/177 Pages) STMicroelectronics – ARM-based 32-bit MCU, 150DMIPs, up to 1 MB Flash/128+4KB RAM

STM32F20xxx
Electrical characteristics
Note:
Table 28. HSE 4-26 MHz oscillator characteristics^{(1) (2)}
Symbol
Parameter
Conditions
Min Typ Max Unit
f_{OSC_IN} Oscillator frequency
4
-
26 MHz
R_F Feedback resistor
- 200 -
kΩ
I_DD HSE current consumption
V_DD=3.3 V,
ESR= 30 Ω,
- 449 -
C_L=5 pF@25 MHz
µA
V_DD=3.3 V,
ESR= 30 Ω,
- 532 -
C_L=10 pF@25 MHz
g_m Oscillator transconductance
t_SU(HSE(3) Startup time
Startup
5
-
- mA/V
V_DD is stabilized
-
2
- ms
1. Resonator characteristics given by the crystal/ceramic resonator manufacturer.
2. Based on characterization, not tested in production.
3. 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
For C_L1 and C_L2, it is recommended to use high-quality external ceramic capacitors in the
5 pF to 25 pF range (typ.), designed for high-frequency applications, and selected to match
the requirements of the crystal or resonator (see Figure 30). C_L1 and C_L2 are usually the
same size. The crystal manufacturer typically specifies a load capacitance which is the
series combination of C_L1 and C_L2. 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.
For information on electing the crystal, refer to the application note AN2867 “Oscillator
design guide for ST microcontrollers” available from the ST website www.st.com.
Figure 30. Typical application with an 8 MHz crystal
Resonator with
integrated capacitors
CL1
8 MH z
resonator
OSC_IN
RF
Bias
controlled
gain
CL2
R_EXT(1)
OSC_OU T
fH_{S E}
STM32F
ai17530
1. R_EXT value depends on the crystal characteristics.
Low-speed external clock generated from a crystal/ceramic resonator
The low-speed external (LSE) clock can be supplied with a 32.768 kHz crystal/ceramic
resonator oscillator. All the information given in this paragraph are based on characterization
results obtained with typical external components specified in Table 29. In the 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).
Doc ID 15818 Rev 9
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